Memory locations used by the ROM

• §1. Zero page memory locations ($A8-$AF)
• §2. OS zero page memory locations
• §3. Page Three
• §4. vduWorkspaceA
• §5. Regular OS variables
• §6. GXR workspace at $0c00-$0c66
• §7. Extended Vector Table
• §8. OS routines and tables
• §9. romSelectRegister
• §10. extendedVectorTableVDUV
• §11. Regular OS entry points

§1. Zero page memory locations ($A8-$AF).

 These locations are available for ROMs to use while they are running, but are not preserved
 between calls.

.tempNumberToPrintLow?Usage of tempNumberToPrintLow:
Chapter 22: Sprite Editor - §89                       = $a8       }
.tempNumberToPrintHigh?Usage of tempNumberToPrintHigh:
Chapter 22: Sprite Editor - §89                      = $a9       } used when printing numbers
.tempNumberPrintedFlag?Usage of tempNumberPrintedFlag:
Chapter 22: Sprite Editor - §89                      = $aa       }

.gcolModeMask0?Usage of gcolModeMask0:
Chapter 11: Shared PLOT subroutines and tables - §7
Chapter 12: VDU commands - §3
Chapter 19: Rectangle copy and move - §5
Chapter 20: Sprite plotting - §1                              = $a8       
.gcolModeMask1?Usage of gcolModeMask1:
Chapter 11: Shared PLOT subroutines and tables - §7
Chapter 12: VDU commands - §3
Chapter 19: Rectangle copy and move - §5
Chapter 20: Sprite plotting - §1                              = $a9       
.gcolModeMask2?Usage of gcolModeMask2:
Chapter 11: Shared PLOT subroutines and tables - §7
Chapter 12: VDU commands - §3
Chapter 19: Rectangle copy and move - §5
Chapter 20: Sprite plotting - §1                              = $aa       
.gcolModeMask3?Usage of gcolModeMask3:
Chapter 11: Shared PLOT subroutines and tables - §7
Chapter 12: VDU commands - §3
Chapter 19: Rectangle copy and move - §5
Chapter 20: Sprite plotting - §1                              = $ab       

.currentSpriteDefinitionLow?Usage of currentSpriteDefinitionLow:
Chapter 22: Sprite Editor - §6, §12, §19, §22, §23, §37, §39, §42, §43, §46, §47, §49, §50, §52, §53, §54, §55, §57, §59, §60, §63, §64, §66, §67, §70, §71, §87                 = $ac       
.currentSpriteDefinitionHigh?Usage of currentSpriteDefinitionHigh:
Chapter 22: Sprite Editor - §12, §19, §22, §23, §49, §54, §55, §57, §63, §64, §66, §67, §70, §71                = $ad       
.seditCurrentSpriteByteLow?Usage of seditCurrentSpriteByteLow:
Chapter 22: Sprite Editor - §5, §6, §12, §29, §59, §60, §61, §62                  = $ae       
.seditCurrentSpriteByteHigh?Usage of seditCurrentSpriteByteHigh:
Chapter 22: Sprite Editor - §5, §6, §12, §59, §60                 = $af       

§2. OS zero page memory locations.

 These locations are owned by the OS. The GXR reads or writes them. Page 3 ($0300-$03ff) is
 where the VDU variables live: i.e. OS variables related to the graphics system.
 Locations $0328-$0349 (.vduWorkspaceA upwards) are used temporarily by the different
 graphics primitive routines.

.vduCurrentPlotByteMask?Usage of vduCurrentPlotByteMask:
Chapter 17: Lines - §12
Chapter 18: Flood fill and horizontal fill - §7, §8, §10, §11, §14
Chapter 19: Rectangle copy and move - §5, §10                     = $d1

    The Electron has a different arrangement of zero page VDU variables
    compared to the BBC machines:
    
                                                 BBC B/B+        Electron
    .vduCurrentPlotByteMask                        $d1             $d1
    .vduGraphicsColourByteOR                       $d4             $de
    .vduGraphicsColourByteEOR                      $d5             $df
    .vduScreenAddressOfGraphicsCursorCellLow       $d6             $d4
    .vduScreenAddressOfGraphicsCursorCellHigh      $d7             $d5
    .vduTempStoreDA                                $da             $d8
    .vduTempStoreDB                                $db             $d9
    .vduTempStoreDC                                $dc             $da
    .vduTempStoreDD                                $dd             $db
    .vduTempStoreDE                                $de             $dc
    .vduTempStoreDF                                $df             $dd
    
    Unfortunately Electron temporary locations $D8 and $D9 are used to hold
    .vduWriteCursorScreenAddress{Low,High} on the BBC B/B+. This means that although the ROM
    contains code to check if it's installed on an incompatible machine, in practice an
    Electron GXR ROM installed on a BBC B/B+ will cause glitches as it scribbles over $D8
    and $D9 and the OS writes to random addresses when it thinks it's writing to the
    screen. In practice this isn't a huge problem, and it seems best not to risk accidentally
    breaking things by trying to tweak the temporary use to avoid accessing $D8 or $D9 until
    after we've successfully checked we *are* running on an Electron.
!if (MACHINE = BBC_B) | (MACHINE = BBC_B_PLUS) {
    .vduGraphicsColourByteOR?Usage of vduGraphicsColourByteOR:
§8
Chapter 11: Shared PLOT subroutines and tables - §7
Chapter 17: Lines - §12
Chapter 18: Flood fill and horizontal fill - §10
Chapter 20: Sprite plotting - §1                    = $d4
    .vduGraphicsColourByteEOR?Usage of vduGraphicsColourByteEOR:
§8
Chapter 11: Shared PLOT subroutines and tables - §7
Chapter 17: Lines - §12
Chapter 18: Flood fill and horizontal fill - §10
Chapter 20: Sprite plotting - §1                   = $d5
    .vduScreenAddressOfGraphicsCursorCellLow?Usage of vduScreenAddressOfGraphicsCursorCellLow:
§8
Chapter 17: Lines - §12, §15
Chapter 18: Flood fill and horizontal fill - §10, §14
Chapter 19: Rectangle copy and move - §5
Chapter 20: Sprite plotting - §1
Chapter 21: Sprite commands - §4    = $d6       } address of the top of the cell
    .vduScreenAddressOfGraphicsCursorCellHigh?Usage of vduScreenAddressOfGraphicsCursorCellHigh:
Chapter 17: Lines - §15
Chapter 19: Rectangle copy and move - §5
Chapter 20: Sprite plotting - §1
Chapter 21: Sprite commands - §4   = $d7       } on screen containing the
                                                            } graphics
                                                            } cursor position
    .vduTempStoreDA?Usage of vduTempStoreDA:
§8
Chapter 4: ROM header and service entry routines - §4
Chapter 5: Parsing star commands - §1, §2
Chapter 6: Parsing OSBYTE (*FX) commands - §3
Chapter 7: Parsing *HELP Commands - §5
Chapter 10: Star commands affecting memory - §5, §8
Chapter 12: VDU commands - §3, §9
Chapter 13: Sprite editor block memory copy - §1, §2
Chapter 17: Lines - §8, §10, §12
Chapter 18: Flood fill and horizontal fill - §10
Chapter 19: Rectangle copy and move - §3, §5, §8, §9
Chapter 20: Sprite plotting - §1
Chapter 21: Sprite commands - §4, §7, §8, §9, §11
Chapter 22: Sprite Editor - §15, §16, §17, §21, §22, §24, §29, §50, §52, §54, §55, §57, §63, §64, §65, §66, §67, §70, §71, §72, §74                             = $da       } store for temporary values,
    .vduTempStoreDB?Usage of vduTempStoreDB:
Chapter 4: ROM header and service entry routines - §4
Chapter 5: Parsing star commands - §1
Chapter 6: Parsing OSBYTE (*FX) commands - §3
Chapter 7: Parsing *HELP Commands - §5
Chapter 10: Star commands affecting memory - §5, §8
Chapter 12: VDU commands - §3
Chapter 13: Sprite editor block memory copy - §2
Chapter 15: Parallelogram and Triangle - §8
Chapter 17: Lines - §12
Chapter 19: Rectangle copy and move - §5
Chapter 21: Sprite commands - §4, §7, §8, §9, §11
Chapter 22: Sprite Editor - §15, §16, §17, §21, §22, §24, §54, §55, §57, §63, §64, §65, §66, §67, §70, §71, §72, §74                             = $db       } used in multiple VDU related
    .vduTempStoreDC?Usage of vduTempStoreDC:
Chapter 4: ROM header and service entry routines - §4
Chapter 5: Parsing star commands - §1
Chapter 10: Star commands affecting memory - §5
Chapter 13: Sprite editor block memory copy - §1, §2
Chapter 17: Lines - §10, §12
Chapter 18: Flood fill and horizontal fill - §4, §5
Chapter 19: Rectangle copy and move - §5, §10
Chapter 21: Sprite commands - §4, §7, §8, §9, §11, §17
Chapter 22: Sprite Editor - §17, §18, §21, §23, §52, §54, §55, §57, §63, §64, §66, §67, §68, §70, §71, §73, §75, §76, §77, §78                             = $dc       } functions.
    .vduTempStoreDD?Usage of vduTempStoreDD:
Chapter 4: ROM header and service entry routines - §4
Chapter 5: Parsing star commands - §1
Chapter 10: Star commands affecting memory - §5
Chapter 13: Sprite editor block memory copy - §2
Chapter 17: Lines - §10, §12
Chapter 18: Flood fill and horizontal fill - §4, §5
Chapter 19: Rectangle copy and move - §5, §10
Chapter 21: Sprite commands - §4, §7, §8, §9, §11, §16
Chapter 22: Sprite Editor - §18, §21, §23, §54, §55, §57, §63, §64, §70, §71, §73, §75, §76, §77, §78                             = $dd
    .vduTempStoreDE?Usage of vduTempStoreDE:
Chapter 4: ROM header and service entry routines - §4
Chapter 7: Parsing *HELP Commands - §1
Chapter 10: Star commands affecting memory - §5, §6
Chapter 11: Shared PLOT subroutines and tables - §5
Chapter 13: Sprite editor block memory copy - §1, §2
Chapter 15: Parallelogram and Triangle - §8, §12
Chapter 16: Circle - §4, §23, §24
Chapter 17: Lines - §10
Chapter 19: Rectangle copy and move - §9
Chapter 21: Sprite commands - §4, §7, §17
Chapter 22: Sprite Editor - §12, §16, §17, §18, §21, §22, §55, §57, §64, §66, §67, §69, §78, §80, §86
Chapter 24: Maths routines - §1, §2                             = $de
    .vduTempStoreDF?Usage of vduTempStoreDF:
Chapter 4: ROM header and service entry routines - §4
Chapter 7: Parsing *HELP Commands - §1
Chapter 10: Star commands affecting memory - §5
Chapter 13: Sprite editor block memory copy - §1, §2
Chapter 16: Circle - §4, §23, §24
Chapter 17: Lines - §10
Chapter 21: Sprite commands - §4, §17
Chapter 22: Sprite Editor - §12, §17, §18, §21, §22, §55, §57, §64, §66, §67, §78, §86
Chapter 24: Maths routines - §2                             = $df
} else if (MACHINE = ELECTRON) {
    .vduGraphicsColourByteOR                    = $de
    .vduGraphicsColourByteEOR                   = $df
    .vduScreenAddressOfGraphicsCursorCellLow    = $d4       } address of the top of the cell
    .vduScreenAddressOfGraphicsCursorCellHigh   = $d5       } on screen containing the
                                                            } graphics
                                                            } cursor position

    .vduTempStoreDA                             = $d8       } store for temporary values,
    .vduTempStoreDB                             = $d9       } used in multiple VDU related
    .vduTempStoreDC                             = $da       } functions.
    .vduTempStoreDD                             = $db
    .vduTempStoreDE                             = $dc
    .vduTempStoreDF                             = $dd
} else {
    +unknown_machine
}

.osbyteA?Usage of osbyteA:
Chapter 6: Parsing OSBYTE (*FX) commands - §5                                    = $ef       }
.oswordA                                    = $ef       } stores register values when

.osbyteX?Usage of osbyteX:
Chapter 6: Parsing OSBYTE (*FX) commands - §1, §2, §5                                    = $f0       } calling .OSBYTE and OSWORD
.oswordX                                    = $f0       }

.osbyteY?Usage of osbyteY:
Chapter 6: Parsing OSBYTE (*FX) commands - §1, §2, §5                                    = $f1       } stores register values when
.oswordY                                    = $f1       } calling .OSBYTE and OSWORD

.stringInputBufferAddressLow?Usage of stringInputBufferAddressLow:
Chapter 5: Parsing star commands - §1, §8
Chapter 7: Parsing *HELP Commands - §1                = $f2       } Start address of input string
.stringInputBufferAddressHigh?Usage of stringInputBufferAddressHigh:
Chapter 5: Parsing star commands - §1               = $f3       }

.currentlySelectedROM?Usage of currentlySelectedROM:
Chapter 4: ROM header and service entry routines - §4
Chapter 5: Parsing star commands - §1
Chapter 7: Parsing *HELP Commands - §1
Chapter 8: Intercepting unknown VDU commands - §2
Chapter 9: Trampoline code for OSWRCH - §2
Chapter 10: Star commands affecting memory - §2, §3                       = $f4       current paged ROM selected

.privateWorkspaceLow?Usage of privateWorkspaceLow:
Chapter 4: ROM header and service entry routines - §4
Chapter 5: Parsing star commands - §1
Chapter 6: Parsing OSBYTE (*FX) commands - §2, §3, §6, §7
Chapter 7: Parsing *HELP Commands - §1
Chapter 8: Intercepting unknown VDU commands - §1, §2
Chapter 10: Star commands affecting memory - §4, §5, §6, §7
Chapter 12: VDU commands - §3, §4, §7, §8, §9
Chapter 14: Point and Rectangle - §5
Chapter 17: Lines - §16, §17
Chapter 18: Flood fill and horizontal fill - §3
Chapter 20: Sprite plotting - §1
Chapter 21: Sprite commands - §4, §7, §8, §11, §16
Chapter 22: Sprite Editor - §17, §18, §19, §21, §22, §28, §48, §49, §58, §76, §78, §79, §80, §87                        = $f8       (OS does not use this location)
.privateWorkspaceHigh?Usage of privateWorkspaceHigh:
Chapter 4: ROM header and service entry routines - §4
Chapter 7: Parsing *HELP Commands - §1
Chapter 8: Intercepting unknown VDU commands - §2
Chapter 18: Flood fill and horizontal fill - §4, §5
Chapter 20: Sprite plotting - §1
Chapter 21: Sprite commands - §7, §11
Chapter 22: Sprite Editor - §79, §80                       = $f9       (OS does not use this location)

.escapeFlag?Usage of escapeFlag:
Chapter 18: Flood fill and horizontal fill - §3                                 = $ff       the ESCAPE flag
                                                        this is set when an ESCAPE character
                                                        (normally .charESCAPE) is entered
                                                        into an input buffer.
                                                        it should be acknowledged using
                                                        .OSBYTE 126. This tells the second
                                                        processor of the event and clears
                                                        the flag.

.page1Start?Usage of page1Start:
Chapter 10: Star commands affecting memory - §8                                 = $0100     page 1 is used for reporting errors

.vectorWRCHVLow?Usage of vectorWRCHVLow:
Chapter 4: ROM header and service entry routines - §4                             = $020e     OSWRCH vector
.vectorWRCHVHigh?Usage of vectorWRCHVHigh:
Chapter 4: ROM header and service entry routines - §4                            = $020f     OSWRCH vector

.vectorVDUVLow?Usage of vectorVDUVLow:
Chapter 4: ROM header and service entry routines - §4
Chapter 8: Intercepting unknown VDU commands - §1
Chapter 12: VDU commands - §1, §6                              = $0226     unrecognised PLOT / VDU 23 commands
.vectorVDUVHigh?Usage of vectorVDUVHigh:
Chapter 4: ROM header and service entry routines - §4
Chapter 8: Intercepting unknown VDU commands - §1                             = $0227     unrecognised PLOT / VDU 23 commands

.lastResetType?Usage of lastResetType:
Chapter 4: ROM header and service entry routines - §4                              = $028d     what type of reset was last done?
                                                               0    Soft reset (BREAK)
                                                               1    Power on
                                                               2    Hard reset (CTRL-BREAK)

§3. Page Three.

.vduVariablesStart?Usage of vduVariablesStart:
§6, §8
Chapter 11: Shared PLOT subroutines and tables - §4, §5
Chapter 12: VDU commands - §3
Chapter 14: Point and Rectangle - §1, §2, §3, §4
Chapter 15: Parallelogram and Triangle - §4, §5, §6, §7, §8, §10, §11, §12
Chapter 16: Circle - §2, §3, §4, §7, §8, §9, §14, §15, §17, §18, §19, §20, §22, §23, §24, §25, §26
Chapter 17: Lines - §1, §2, §3, §4, §5, §6, §7, §8, §9, §10, §12
Chapter 18: Flood fill and horizontal fill - §3, §6, §8, §11, §13
Chapter 19: Rectangle copy and move - §5, §9, §10
Chapter 20: Sprite plotting - §1
Chapter 21: Sprite commands - §4
Chapter 23: Ellipse - §2, §3, §4, §5, §6, §7, §8, §9
Chapter 24: Maths routines - §1, §2, §3                          = $0300     

.vduGraphicsWindowPixelsLeftLow?Usage of vduGraphicsWindowPixelsLeftLow:
Chapter 17: Lines - §8, §12
Chapter 18: Flood fill and horizontal fill - §7
Chapter 19: Rectangle copy and move - §5
Chapter 20: Sprite plotting - §1
Chapter 21: Sprite commands - §4             = $0300     }
.vduGraphicsWindowPixelsLeftHigh?Usage of vduGraphicsWindowPixelsLeftHigh:
Chapter 17: Lines - §8
Chapter 18: Flood fill and horizontal fill - §7            = $0301     }
.vduGraphicsWindowPixelsBottomLow?Usage of vduGraphicsWindowPixelsBottomLow:
Chapter 17: Lines - §10, §12
Chapter 20: Sprite plotting - §1
Chapter 21: Sprite commands - §4           = $0302     }
.vduGraphicsWindowPixelsBottomHigh?Usage of vduGraphicsWindowPixelsBottomHigh:
Chapter 17: Lines - §10          = $0303     }
.vduGraphicsWindowPixelsRightLow?Usage of vduGraphicsWindowPixelsRightLow:
Chapter 17: Lines - §8, §12
Chapter 18: Flood fill and horizontal fill - §8
Chapter 19: Rectangle copy and move - §5
Chapter 20: Sprite plotting - §1
Chapter 21: Sprite commands - §4            = $0304     } graphics window in pixels
.vduGraphicsWindowPixelsRightHigh?Usage of vduGraphicsWindowPixelsRightHigh:
Chapter 17: Lines - §8
Chapter 18: Flood fill and horizontal fill - §8           = $0305     }
.vduGraphicsWindowPixelsTopLow?Usage of vduGraphicsWindowPixelsTopLow:
Chapter 17: Lines - §10, §12
Chapter 20: Sprite plotting - §1
Chapter 21: Sprite commands - §4              = $0306     }
.vduGraphicsWindowPixelsTopHigh?Usage of vduGraphicsWindowPixelsTopHigh:
Chapter 17: Lines - §10             = $0307     }

.vduOldGraphicsCursorPixelsXLow?Usage of vduOldGraphicsCursorPixelsXLow:
Chapter 11: Shared PLOT subroutines and tables - §4
Chapter 12: VDU commands - §4
Chapter 15: Parallelogram and Triangle - §4, §5
Chapter 16: Circle - §2, §3, §7, §8, §9, §10, §14, §15, §17
Chapter 18: Flood fill and horizontal fill - §4, §6, §7, §8, §15, §18
Chapter 19: Rectangle copy and move - §5
Chapter 21: Sprite commands - §4
Chapter 23: Ellipse - §5, §8, §9             = $0314     }
.vduOldGraphicsCursorPixelsXHigh?Usage of vduOldGraphicsCursorPixelsXHigh:
Chapter 11: Shared PLOT subroutines and tables - §4
Chapter 15: Parallelogram and Triangle - §4
Chapter 16: Circle - §10
Chapter 18: Flood fill and horizontal fill - §4, §6, §7, §8
Chapter 23: Ellipse - §8, §9            = $0315     } old graphics cursor in pixels
.vduOldGraphicsCursorPixelsYLow?Usage of vduOldGraphicsCursorPixelsYLow:
Chapter 11: Shared PLOT subroutines and tables - §4
Chapter 16: Circle - §11, §12
Chapter 18: Flood fill and horizontal fill - §4, §6
Chapter 23: Ellipse - §5, §8, §9             = $0316     }
.vduOldGraphicsCursorPixelsYHigh?Usage of vduOldGraphicsCursorPixelsYHigh:
Chapter 11: Shared PLOT subroutines and tables - §4
Chapter 16: Circle - §11, §12
Chapter 18: Flood fill and horizontal fill - §6
Chapter 23: Ellipse - §8, §9            = $0317     }

.vduGraphicsCursorVerticalOffsetInCell?Usage of vduGraphicsCursorVerticalOffsetInCell:
Chapter 18: Flood fill and horizontal fill - §14
Chapter 20: Sprite plotting - §1
Chapter 21: Sprite commands - §4      = $031A     offset within a character cell of
                                                        the current graphics cursor Y
                                                        coordinate

.vdu23NParameter?Usage of vdu23NParameter:
Chapter 12: VDU commands - §5, §7, §9                            = .vduQueueEndByte - 7  VDU 23,N
.vdu23SChooseOrSGetSpriteNumberParameter?Usage of vdu23SChooseOrSGetSpriteNumberParameter:
Chapter 12: VDU commands - §5    = .vduQueueEndByte - 6  VDU 23,27,N

.vdu25ParameterPlotType?Usage of vdu25ParameterPlotType:
Chapter 12: VDU commands - §1, §3
Chapter 17: Lines - §11
Chapter 19: Rectangle copy and move - §4                     = .vduQueueEndByte - 4
.vdu25ParameterXLow?Usage of vdu25ParameterXLow:
Chapter 12: VDU commands - §3, §4
Chapter 14: Point and Rectangle - §1, §2
Chapter 15: Parallelogram and Triangle - §4, §5
Chapter 16: Circle - §2, §3, §14, §15, §17
Chapter 17: Lines - §12
Chapter 18: Flood fill and horizontal fill - §3, §11, §12, §13, §15, §18
Chapter 19: Rectangle copy and move - §5
Chapter 20: Sprite plotting - §1
Chapter 23: Ellipse - §5                         = .vduQueueEndByte - 3
.vdu25ParameterXHigh?Usage of vdu25ParameterXHigh:
Chapter 15: Parallelogram and Triangle - §4
Chapter 18: Flood fill and horizontal fill - §3, §11, §12                        = .vduQueueEndByte - 2
.vdu25ParameterYLow?Usage of vdu25ParameterYLow:
Chapter 17: Lines - §12
Chapter 18: Flood fill and horizontal fill - §3, §11, §12
Chapter 23: Ellipse - §5                         = .vduQueueEndByte - 1
.vdu25ParameterYHigh                        = .vduQueueEndByte

.vduQueueEndByte?Usage of vduQueueEndByte:
Chapter 18: Flood fill and horizontal fill - §11                            = $0323     } nine bytes for vdu queue (end)

.vduGraphicsCursorPixelsXLow?Usage of vduGraphicsCursorPixelsXLow:
Chapter 12: VDU commands - §4
Chapter 14: Point and Rectangle - §4
Chapter 15: Parallelogram and Triangle - §4, §5
Chapter 16: Circle - §2, §3, §7, §8, §9, §14, §15, §17, §22
Chapter 17: Lines - §12
Chapter 18: Flood fill and horizontal fill - §4, §6, §8, §9, §12, §15, §18
Chapter 23: Ellipse - §5                = $0324     current graphics cursor position in
.vduGraphicsCursorPixelsXHigh?Usage of vduGraphicsCursorPixelsXHigh:
Chapter 15: Parallelogram and Triangle - §4
Chapter 18: Flood fill and horizontal fill - §4, §6, §8, §9, §12               = $0325     pixels
.vduGraphicsCursorPixelsYLow?Usage of vduGraphicsCursorPixelsYLow:
Chapter 18: Flood fill and horizontal fill - §6, §12                = $0326     
.vduGraphicsCursorPixelsYHigh?Usage of vduGraphicsCursorPixelsYHigh:
Chapter 18: Flood fill and horizontal fill - §6               = $0327     

§4. vduWorkspaceA.

 VDU variables used by the GXR ROM for general workspace use when plotting or sprite editing.
 We give more helpful names to these workspace variables for specific routines.

.vduWorkspaceA?Usage of vduWorkspaceA:
Chapter 4: ROM header and service entry routines - §4
Chapter 14: Point and Rectangle - §3, §4
Chapter 15: Parallelogram and Triangle - §4
Chapter 17: Lines - §13
Chapter 18: Flood fill and horizontal fill - §5, §12
Chapter 19: Rectangle copy and move - §5
Chapter 20: Sprite plotting - §1
Chapter 21: Sprite commands - §4
Chapter 22: Sprite Editor - §61, §62                              = $0328     
.vduWorkspaceB?Usage of vduWorkspaceB:
Chapter 15: Parallelogram and Triangle - §4
Chapter 17: Lines - §13
Chapter 18: Flood fill and horizontal fill - §5, §12
Chapter 20: Sprite plotting - §1
Chapter 21: Sprite commands - §4
Chapter 22: Sprite Editor - §21                              = $0329     
.vduWorkspaceC?Usage of vduWorkspaceC:
Chapter 4: ROM header and service entry routines - §4
Chapter 14: Point and Rectangle - §3
Chapter 18: Flood fill and horizontal fill - §3, §5, §12
Chapter 19: Rectangle copy and move - §5, §6, §7
Chapter 20: Sprite plotting - §1
Chapter 21: Sprite commands - §4
Chapter 22: Sprite Editor - §21, §22                              = $032A     
.vduWorkspaceD?Usage of vduWorkspaceD:
Chapter 14: Point and Rectangle - §3
Chapter 18: Flood fill and horizontal fill - §5, §11, §12
Chapter 19: Rectangle copy and move - §5, §6, §7
Chapter 20: Sprite plotting - §1
Chapter 21: Sprite commands - §4
Chapter 22: Sprite Editor - §21, §23, §48, §49                              = $032B     
.vduWorkspaceE?Usage of vduWorkspaceE:
Chapter 14: Point and Rectangle - §3
Chapter 18: Flood fill and horizontal fill - §5, §11, §12
Chapter 19: Rectangle copy and move - §5
Chapter 20: Sprite plotting - §1
Chapter 21: Sprite commands - §4                              = $032C     
.vduWorkspaceF?Usage of vduWorkspaceF:
Chapter 18: Flood fill and horizontal fill - §3, §4, §5
Chapter 20: Sprite plotting - §1
Chapter 21: Sprite commands - §4                              = $032D     
.vduWorkspaceG?Usage of vduWorkspaceG:
Chapter 14: Point and Rectangle - §3
Chapter 18: Flood fill and horizontal fill - §3, §4
Chapter 19: Rectangle copy and move - §5, §7
Chapter 20: Sprite plotting - §1
Chapter 21: Sprite commands - §4                              = $032E     
.vduWorkspaceH?Usage of vduWorkspaceH:
Chapter 14: Point and Rectangle - §3
Chapter 18: Flood fill and horizontal fill - §7, §8, §10
Chapter 19: Rectangle copy and move - §7                              = $032F     
.vduWorkspaceI?Usage of vduWorkspaceI:
Chapter 18: Flood fill and horizontal fill - §3, §14, §15, §18
Chapter 19: Rectangle copy and move - §5
Chapter 20: Sprite plotting - §1
Chapter 22: Sprite Editor - §5                              = $0330     
.vduWorkspaceJ?Usage of vduWorkspaceJ:
Chapter 20: Sprite plotting - §1                              = $0331     
.vduWorkspaceK?Usage of vduWorkspaceK:
Chapter 19: Rectangle copy and move - §5
Chapter 20: Sprite plotting - §1                              = $0332     
.vduWorkspaceL                              = $0333     
.vduWorkspaceM?Usage of vduWorkspaceM:
Chapter 19: Rectangle copy and move - §5
Chapter 20: Sprite plotting - §1                              = $0334     
.vduWorkspaceN                              = $0335     
.vduWorkspaceO?Usage of vduWorkspaceO:
Chapter 19: Rectangle copy and move - §5
Chapter 20: Sprite plotting - §1                              = $0336     
.vduWorkspaceP?Usage of vduWorkspaceP:
Chapter 19: Rectangle copy and move - §5                              = $0337     
.vduWorkspaceQ?Usage of vduWorkspaceQ:
Chapter 19: Rectangle copy and move - §5
Chapter 20: Sprite plotting - §1                              = $0338     
.vduWorkspaceR                              = $0339     
.vduWorkspaceS?Usage of vduWorkspaceS:
Chapter 19: Rectangle copy and move - §5
Chapter 20: Sprite plotting - §1                              = $033A     
.vduWorkspaceT                              = $033B     
.vduWorkspaceU?Usage of vduWorkspaceU:
Chapter 19: Rectangle copy and move - §5                              = $033C     
.vduWorkspaceV?Usage of vduWorkspaceV:
Chapter 19: Rectangle copy and move - §5                              = $033D     
.vduWorkspaceW?Usage of vduWorkspaceW:
Chapter 19: Rectangle copy and move - §5                              = $033E     
.vduWorkspaceX                              = $033F     
.vduWorkspaceY?Usage of vduWorkspaceY:
Chapter 19: Rectangle copy and move - §5                              = $0340     
.vduWorkspaceZ?Usage of vduWorkspaceZ:
Chapter 19: Rectangle copy and move - §5                              = $0341     
.vduWorkspaceAA                             = $0342     
.vduWorkspaceBB                             = $0343     
.vduWorkspaceCC?Usage of vduWorkspaceCC:
Chapter 23: Ellipse - §4, §8                             = $0344     
.vduWorkspaceDD                             = $0345     

***** Line drawing/tracking variables *****
.line1StartPointX?Usage of line1StartPointX:
Chapter 16: Circle - §14, §15, §22
Chapter 17: Lines - §10, §12                           = $0328     initial and current point X [2 bytes]
.line1StartPointY?Usage of line1StartPointY:
Chapter 17: Lines - §10, §12                           = $032a     initial and current point Y [2 bytes]
.line1AbsDeltaX?Usage of line1AbsDeltaX:
Chapter 17: Lines - §12                             = $032c     abs(deltaX)                 [2 bytes]
.line1AbsDeltaY?Usage of line1AbsDeltaY:
Chapter 15: Parallelogram and Triangle - §8
Chapter 17: Lines - §10, §12                             = $032e     abs(deltaY)                 [2 bytes]
.line1ErrorTerm?Usage of line1ErrorTerm:
Chapter 17: Lines - §10, §12                             = $0330     Bresenham error term        [2 bytes]
.line1Signs?Usage of line1Signs:
Chapter 17: Lines - §12                                 = $0332     signs of deltaY (top bit) and deltaX
                                                        (bit 6) [1 byte]

.line2StartPointX?Usage of line2StartPointX:
Chapter 15: Parallelogram and Triangle - §4, §8
Chapter 16: Circle - §14, §15, §17, §20, §22                           = $0334     initial and current point X [2 bytes]
.line2StartPointY                           = $0336     initial and current point Y [2 bytes]
.line2AbsDeltaX?Usage of line2AbsDeltaX:
Chapter 15: Parallelogram and Triangle - §4, §8
Chapter 16: Circle - §17                             = $0338     abs(deltaX)                 [2 bytes]
.line2AbsDeltaY?Usage of line2AbsDeltaY:
Chapter 15: Parallelogram and Triangle - §4, §8
Chapter 16: Circle - §17                             = $033a     abs(deltaY)                 [2 bytes]
.line2ErrorTerm?Usage of line2ErrorTerm:
Chapter 15: Parallelogram and Triangle - §4, §8
Chapter 16: Circle - §17                             = $033c     Bresenham error term        [2 bytes]
.line2Signs?Usage of line2Signs:
Chapter 15: Parallelogram and Triangle - §4, §8
Chapter 16: Circle - §17                                 = $033e     signs of deltaY (top bit) and deltaX
                                                        (bit 6) [1 byte]

.line3StartPointX?Usage of line3StartPointX:
Chapter 15: Parallelogram and Triangle - §4, §7, §8
Chapter 16: Circle - §14, §15, §17, §20, §22                           = $033f     initial and current point X [2 bytes]
.line3StartPointY                           = $0341     initial and current point Y [2 bytes]
.line3AbsDeltaX?Usage of line3AbsDeltaX:
Chapter 15: Parallelogram and Triangle - §7
Chapter 16: Circle - §14, §17                             = $0343     abs(deltaX)                 [2 bytes]
.line3AbsDeltaY?Usage of line3AbsDeltaY:
Chapter 15: Parallelogram and Triangle - §7
Chapter 16: Circle - §14, §17                             = $0345     abs(deltaY)                 [2 bytes]
.line3ErrorTerm?Usage of line3ErrorTerm:
Chapter 15: Parallelogram and Triangle - §7
Chapter 16: Circle - §14, §17                             = $0347     Bresenham error term        [2 bytes]
.line3Signs?Usage of line3Signs:
Chapter 15: Parallelogram and Triangle - §7
Chapter 16: Circle - §14, §17                                 = $0349     signs of deltaY (top bit) and deltaX
                                                        (bit 6) [1 byte]

***** Triangle drawing variables *****
.triangleRowLeftPointX?Usage of triangleRowLeftPointX:
Chapter 15: Parallelogram and Triangle - §6, §7, §8, §11                      = $032c     }
.triangleRowLeftPointY                      = $032e     } the current row has a leftmost
.triangleRowRightPointX?Usage of triangleRowRightPointX:
Chapter 15: Parallelogram and Triangle - §6, §7, §8, §11                     = $0330     } and rightmost pixel to fill
.triangleRowRightPointY                     = $0332     }

***** Circle drawing variables *****
.circlePointLeftXLow?Usage of circlePointLeftXLow:
Chapter 16: Circle - §2, §3, §7, §9, §10, §19                        = $032c     }
.circlePointLeftXHigh?Usage of circlePointLeftXHigh:
Chapter 16: Circle - §10                       = $032d     }
.circlePointLeftYLow?Usage of circlePointLeftYLow:
Chapter 16: Circle - §11, §12, §25                        = $032e     }
.circlePointLeftYHigh?Usage of circlePointLeftYHigh:
Chapter 16: Circle - §11, §12, §25                       = $032f     } the current row has a leftmost
.circlePointRightXLow?Usage of circlePointRightXLow:
Chapter 16: Circle - §2, §3, §7, §9, §10, §19                       = $0330     } and a rightmost point to fill
.circlePointRightXHigh?Usage of circlePointRightXHigh:
Chapter 16: Circle - §10                      = $0331     }
.circlePointRightYLow?Usage of circlePointRightYLow:
Chapter 16: Circle - §11, §12                       = $0332     }
.circlePointRightYHigh?Usage of circlePointRightYHigh:
Chapter 16: Circle - §11, §12                      = $0333     }

***** Move/copy rectangle variables *****
.rectSourceLeft?Usage of rectSourceLeft:
Chapter 19: Rectangle copy and move - §5                             = $0328     left   edge of src rect [2 bytes]
.rectSourceBottom                           = $032a     bottom edge of src rect [2 bytes]
.rectSourceRight?Usage of rectSourceRight:
Chapter 19: Rectangle copy and move - §5                            = $032c     right  edge of src rect [2 bytes]
.rectSourceTop                              = $032e     top    edge of src rect [2 bytes]

.rectDestinationLeft?Usage of rectDestinationLeft:
Chapter 19: Rectangle copy and move - §5                        = $0334     left   edge of dest rect [2 bytes]
.rectDestinationBottom                      = $0336     bottom edge of dest rect [2 bytes]
.rectDestinationRight?Usage of rectDestinationRight:
Chapter 19: Rectangle copy and move - §5                       = $0338     right  edge of dest rect [2 bytes]
.rectDestinationTop?Usage of rectDestinationTop:
Chapter 19: Rectangle copy and move - §5                         = $033a     top    edge of dest rect [2 bytes]

.rectCopyShiftToNextByte?Usage of rectCopyShiftToNextByte:
Chapter 19: Rectangle copy and move - §5                    = $0342     
.rectCopyNumberOfTimesToShiftByte?Usage of rectCopyNumberOfTimesToShiftByte:
Chapter 19: Rectangle copy and move - §5           = $0343     number of times to shift right each
                                                        byte when copying/moving
.rectCopyByteWidth?Usage of rectCopyByteWidth:
Chapter 19: Rectangle copy and move - §5                          = $0344     width in bytes of area to copy / move
.rectCopyPlotType?Usage of rectCopyPlotType:
Chapter 19: Rectangle copy and move - §5                           = $0345     
.rectCopyByteMask?Usage of rectCopyByteMask:
Chapter 19: Rectangle copy and move - §5                           = $0346     byte mask for writing the
                                                        initial/final byte of a row
.rectCopyShiftingLeftFlag?Usage of rectCopyShiftingLeftFlag:
Chapter 19: Rectangle copy and move - §5                   = $0347     top bit set means we are shifting
                                                        pixels left within each byte

***** Sprite editing variables *****
.seditCurrentVisibleX?Usage of seditCurrentVisibleX:
Chapter 22: Sprite Editor - §4, §5, §7, §12, §14, §22, §30, §31, §32, §33, §35, §36, §37, §41, §43, §54, §60, §66, §67, §87                       = $033C     X offset within the visible area
                                                        of the current cursor
.seditCurrentVisibleY?Usage of seditCurrentVisibleY:
Chapter 22: Sprite Editor - §4, §6, §7, §12, §14, §22, §30, §31, §32, §34, §38, §39, §45, §47, §53, §59, §63, §64, §87                       = $033D     Y offset within visible area of
                                                        the current cursor
.seditCurrentVisibleByteMask?Usage of seditCurrentVisibleByteMask:
Chapter 22: Sprite Editor - §5, §7, §22, §29, §30, §31, §35, §36, §37, §41, §54, §60, §61, §62, §67, §68                = $033E     a bitmask for the current pixel
                                                        within the current sprite byte
.seditCurrentX?Usage of seditCurrentX:
Chapter 22: Sprite Editor - §12, §22, §36, §37, §40, §41, §42, §43, §54, §60, §66, §67, §87                              = $033F     left pixel coordinate of large sprite
.seditCurrentSpriteVisibleWidth?Usage of seditCurrentSpriteVisibleWidth:
Chapter 22: Sprite Editor - §4, §5, §22, §30, §31, §36, §37, §42, §43, §52, §54             = $0340     width of visible area of sprite (in
                                                        sprite pixels)
.seditCurrentY?Usage of seditCurrentY:
Chapter 22: Sprite Editor - §12, §22, §38, §39, §44, §45, §46, §47, §53, §59, §63, §64, §87                              = $0341     bottom pixel coordinate of large
                                                        sprite
.seditCurrentSpriteVisibleHeight?Usage of seditCurrentSpriteVisibleHeight:
Chapter 22: Sprite Editor - §4, §6, §7, §22, §30, §31, §38, §39, §46, §47, §50, §53            = $0342     height of visible area of sprite (in
                                                        sprite pixels)
.seditScreenXOffsetWithinCurrentByte?Usage of seditScreenXOffsetWithinCurrentByte:
Chapter 22: Sprite Editor - §9, §10, §22, §30, §36, §37, §41, §43, §54        = $0343     Screen X offset within the current
                                                        sprite byte scaled up to screen
                                                        coordinates for the large sprite.
                                                        (in increments of
                                                        '.seditXCoordinateIncrement')

.plotPointXLow?Usage of plotPointXLow:
Chapter 22: Sprite Editor - §5, §9, §10, §14, §32, §83
Chapter 23: Ellipse - §8, §9                              = $0344     }
.plotPointXHigh?Usage of plotPointXHigh:
Chapter 22: Sprite Editor - §5, §9, §10, §14, §32, §83
Chapter 23: Ellipse - §8, §9                             = $0345     } screen coordinates when PLOTting
.plotPointYLow?Usage of plotPointYLow:
Chapter 22: Sprite Editor - §6, §9, §14, §32, §84
Chapter 23: Ellipse - §8, §9                              = $0346     } (e.g. in the sprite editor)
.plotPointYHigh?Usage of plotPointYHigh:
Chapter 22: Sprite Editor - §6, §9, §14, §32, §84
Chapter 23: Ellipse - §8, §9                             = $0347     }

.seditBackgroundColour?Usage of seditBackgroundColour:
Chapter 22: Sprite Editor - §22, §26, §27, §29, §87                      = $0348     

***** Ellipse variables *****
.ellipse256AspectRatioLow?Usage of ellipse256AspectRatioLow:
Chapter 23: Ellipse - §5, §7                   = $0328     
.ellipse256AspectRatioMid?Usage of ellipse256AspectRatioMid:
Chapter 23: Ellipse - §4, §5, §7                   = $0329     256 * (height / centre row width)
.ellipse256AspectRatioHigh?Usage of ellipse256AspectRatioHigh:
Chapter 23: Ellipse - §7                  = $032a     

.ellipse256ShearLow?Usage of ellipse256ShearLow:
Chapter 23: Ellipse - §5, §7                         = $032b     
.ellipse256ShearMid?Usage of ellipse256ShearMid:
Chapter 23: Ellipse - §5, §7                         = $032c     256 * abs(top X - centre X)
.ellipse256ShearHigh?Usage of ellipse256ShearHigh:
Chapter 23: Ellipse - §7                        = $032d     

.ellipseHalfHeightCounterLow?Usage of ellipseHalfHeightCounterLow:
Chapter 23: Ellipse - §5, §7                = $032e     half the height of the ellipse
.ellipseHalfHeightCounterHigh?Usage of ellipseHalfHeightCounterHigh:
Chapter 23: Ellipse - §2, §3, §5, §7               = $032f     

.ellipseHalfHeightSquaredLow?Usage of ellipseHalfHeightSquaredLow:
Chapter 23: Ellipse - §5, §7                = $0330     
.ellipseHalfHeightSquaredMid1?Usage of ellipseHalfHeightSquaredMid1:
Chapter 23: Ellipse - §7               = $0331     (half the height) squared
.ellipseHalfHeightSquaredMid2?Usage of ellipseHalfHeightSquaredMid2:
Chapter 23: Ellipse - §7               = $0332     
.ellipseHalfHeightSquaredHigh?Usage of ellipseHalfHeightSquaredHigh:
Chapter 23: Ellipse - §7               = $0333     

.ellipsePointCLow?Usage of ellipsePointCLow:
Chapter 23: Ellipse - §2, §5, §7                           = $0334     
.ellipsePointCHigh?Usage of ellipsePointCHigh:
Chapter 23: Ellipse - §2                          = $0335     
.ellipsePointDLow?Usage of ellipsePointDLow:
Chapter 23: Ellipse - §2, §5                           = $0336     
.ellipsePointDHigh                          = $0337     

.ellipseLeftPointLow?Usage of ellipseLeftPointLow:
Chapter 23: Ellipse - §2, §3, §5, §6, §7                        = $0338     
.ellipseLeftPointHigh?Usage of ellipseLeftPointHigh:
Chapter 23: Ellipse - §2, §6                       = $0339     

.ellipseRightPointLow?Usage of ellipseRightPointLow:
Chapter 23: Ellipse - §2, §3, §5, §6                       = $033a     
.ellipseRightPointHigh?Usage of ellipseRightPointHigh:
Chapter 23: Ellipse - §2, §6                      = $033b     

.ellipsePointALow?Usage of ellipsePointALow:
Chapter 23: Ellipse - §2, §3, §5, §6, §7                           = $033c     
.ellipsePointAHigh?Usage of ellipsePointAHigh:
Chapter 23: Ellipse - §6, §7                          = $033d     
.ellipsePointBLow?Usage of ellipsePointBLow:
Chapter 23: Ellipse - §2, §3, §5, §6, §7                           = $033e     
.ellipsePointBHigh?Usage of ellipsePointBHigh:
Chapter 23: Ellipse - §6, §7                          = $033f     

.ellipsePointELow?Usage of ellipsePointELow:
Chapter 23: Ellipse - §4, §9                           = $0340     
.ellipsePointEHigh?Usage of ellipsePointEHigh:
Chapter 23: Ellipse - §9                          = $0341     

.ellipseCurrentOffsetXLow?Usage of ellipseCurrentOffsetXLow:
Chapter 23: Ellipse - §2, §8, §9                   = $0342     
.ellipseCurrentOffsetXHigh?Usage of ellipseCurrentOffsetXHigh:
Chapter 23: Ellipse - §2, §8, §9                  = $0343     

.ellipsePointFLow                           = $0344     
.ellipsePointFHigh                          = $0345     

§5. Regular OS variables.

.vduBytesPerCharacterRowLow?Usage of vduBytesPerCharacterRowLow:
Chapter 17: Lines - §15                 = $0352     
.vduBytesPerCharacterRowHigh?Usage of vduBytesPerCharacterRowHigh:
Chapter 17: Lines - §15                = $0353     
.vduScreenSizeHighByte?Usage of vduScreenSizeHighByte:
Chapter 17: Lines - §15                      = $0354     
.vduCurrentScreenMODE?Usage of vduCurrentScreenMODE:
Chapter 12: VDU commands - §8, §9
Chapter 16: Circle - §4
Chapter 21: Sprite commands - §4
Chapter 22: Sprite Editor - §5, §6, §9, §11, §14, §22, §30, §36, §37, §43, §50, §52, §54, §87                       = $0355     

.vduForegroundGraphicsColour?Usage of vduForegroundGraphicsColour:
Chapter 12: VDU commands - §3
Chapter 14: Point and Rectangle - §5
Chapter 22: Sprite Editor - §5, §6, §29                = $0359     } byte the given colour
.vduBackgroundGraphicsColour?Usage of vduBackgroundGraphicsColour:
§8
Chapter 18: Flood fill and horizontal fill - §14
Chapter 19: Rectangle copy and move - §5
Chapter 21: Sprite commands - §4                = $035A     }
.vduForegroundGCOLMode?Usage of vduForegroundGCOLMode:
Chapter 12: VDU commands - §3
Chapter 14: Point and Rectangle - §5
Chapter 22: Sprite Editor - §5, §6                      = $035B     GCOL foreground mode
                                                        (0=Normal, 1=OR, 2=AND, 3=EOR,
                                                        4=Invert)
.vduBackgroundGCOLMode                      = $035C     GCOL background mode
                                                        (0=Normal, 1=OR, 2=AND, 3=EOR,
                                                        4=Invert)
.vduJumpVectorLow?Usage of vduJumpVectorLow:
Chapter 9: Trampoline code for OSWRCH - §1                           = $035D     
.vduJumpVectorHigh?Usage of vduJumpVectorHigh:
Chapter 9: Trampoline code for OSWRCH - §1                          = $035E     

.vduNumberOfLogicalColoursMinusOne?Usage of vduNumberOfLogicalColoursMinusOne:
Chapter 12: VDU commands - §9          = $0360     
.vduPixelsPerByteMinusOne?Usage of vduPixelsPerByteMinusOne:
Chapter 5: Parsing star commands - §1
Chapter 12: VDU commands - §3, §6
Chapter 19: Rectangle copy and move - §5, §10
Chapter 20: Sprite plotting - §1
Chapter 21: Sprite commands - §4
Chapter 22: Sprite Editor - §5, §61, §66, §67, §69                   = $0361     

.vduColourMaskLeft?Usage of vduColourMaskLeft:
Chapter 22: Sprite Editor - §5, §22, §30, §37, §41, §60, §67                          = $0362     colour mask left.  Bits for the
                                                        setting the leftmost pixel of a
                                                        byte to white:
                                                        MODE 0,3,4,6,7    = $80
                                                        MODE 1,5          = $88
                                                        MODE 2            = $AA
.vduColourMaskRight?Usage of vduColourMaskRight:
Chapter 22: Sprite Editor - §36, §43, §54, §60, §66, §69                         = $0363     colour mask right. Bits for the
                                                        setting the rightmost pixel of a
                                                        byte to white:
                                                        MODE 0,3,4,6,7    = $01
                                                        MODE 1,5          = $11
                                                        MODE 2            = $55

§6. GXR workspace at $0c00-$0c66.

 Page C normally holds soft character definitions for chars 224-255 but for the duration of
 a PLOT command the range $0c00-$0c66 is cached in private workspace. Thus we can use the
 start of page C as workspace, detailed below.

.softCharacterDefinitions?Usage of softCharacterDefinitions:
Chapter 12: VDU commands - §3, §4                   = $0c00     
.fillPattern?Usage of fillPattern:
Chapter 11: Shared PLOT subroutines and tables - §7
Chapter 12: VDU commands - §3
Chapter 19: Rectangle copy and move - §5                                = $0c00     current fill pattern [8 bytes]
.currentDotDashPattern?Usage of currentDotDashPattern:
Chapter 17: Lines - §12, §16                      = $0c08     current dot-dash pattern [8 bytes]

.currentDotDashPatternBitLength?Usage of currentDotDashPatternBitLength:
Chapter 17: Lines - §12             = $0c10

Temporary current dot-dash line state [3 bytes]
.currentDotDashPatternNumBitsRemaining?Usage of currentDotDashPatternNumBitsRemaining:
Chapter 17: Lines - §12, §17      = $0c11
.currentDotDashPatternBitMask?Usage of currentDotDashPatternBitMask:
Chapter 17: Lines - §12, §17               = $0c12
.currentDotDashPatternByte?Usage of currentDotDashPatternByte:
Chapter 17: Lines - §12, §17                  = $0c13

.gxrScratchspace1?Usage of gxrScratchspace1:
Chapter 15: Parallelogram and Triangle - §4, §8
Chapter 17: Lines - §12
Chapter 19: Rectangle copy and move - §5                           = $0c14
.gxrScratchspace2?Usage of gxrScratchspace2:
Chapter 15: Parallelogram and Triangle - §4, §7, §8
Chapter 19: Rectangle copy and move - §5                           = $0c15
.gxrScratchspace3?Usage of gxrScratchspace3:
Chapter 14: Point and Rectangle - §4
Chapter 15: Parallelogram and Triangle - §8, §9, §12
Chapter 17: Lines - §1, §2, §9, §10, §12
Chapter 19: Rectangle copy and move - §5, §9                           = $0c16

$0c17 onwards holds temporary variables that are not remembered between calls to the ROM.
They are used for multiple purposes, so have different names with the same addresses.
.gxrCurrentPattern?Usage of gxrCurrentPattern:
Chapter 14: Point and Rectangle - §5
Chapter 18: Flood fill and horizontal fill - §14
Chapter 19: Rectangle copy and move - §5                          = $0c17     current fill pattern [8 bytes]
.rectCopyRowCache?Usage of rectCopyRowCache:
Chapter 19: Rectangle copy and move - §5                           = $0c17     the current row data stored during
                                                        a rectangle copy ($0c17-$0c66)
                                                        [80 bytes]

General purpose temporary variables e.g. Used when sorting vertices for triangle or
parallelogram
.gxrTemp1?Usage of gxrTemp1:
Chapter 15: Parallelogram and Triangle - §4, §7
Chapter 16: Circle - §4, §5, §13
Chapter 23: Ellipse - §5                                   = $0c17
.gxrTemp2?Usage of gxrTemp2:
Chapter 15: Parallelogram and Triangle - §4, §7
Chapter 16: Circle - §4, §5, §13
Chapter 23: Ellipse - §5                                   = $0c18
.gxrTemp3?Usage of gxrTemp3:
Chapter 15: Parallelogram and Triangle - §4, §5, §7                                   = $0c19
.gxrTemp4?Usage of gxrTemp4:
Chapter 15: Parallelogram and Triangle - §4
Chapter 16: Circle - §4, §5, §13
Chapter 23: Ellipse - §5                                   = $0c1a
.gxrTemp5?Usage of gxrTemp5:
Chapter 16: Circle - §5, §13                                   = $0c1b
.gxrTemp6                                   = $0c1c
.gxrTemp7                                   = $0c1d

***** For multiply *****
.multiplicand0?Usage of multiplicand0:
Chapter 16: Circle - §17
Chapter 24: Maths routines - §5                              = $0c17
.multiplicand1?Usage of multiplicand1:
Chapter 24: Maths routines - §5                              = $0c18
.multiplicand2?Usage of multiplicand2:
Chapter 24: Maths routines - §4, §5                              = $0c19

.multiplier0?Usage of multiplier0:
Chapter 16: Circle - §17
Chapter 23: Ellipse - §7
Chapter 24: Maths routines - §5                                = $0c1a
.multiplier1?Usage of multiplier1:
Chapter 23: Ellipse - §7
Chapter 24: Maths routines - §5                                = $0c1b
.multiplier2?Usage of multiplier2:
Chapter 23: Ellipse - §7
Chapter 24: Maths routines - §4, §5                                = $0c1c

.product0?Usage of product0:
Chapter 16: Circle - §17
Chapter 24: Maths routines - §5                                   = $0c1a
.product1?Usage of product1:
Chapter 23: Ellipse - §7                                   = $0c1b
.product2?Usage of product2:
Chapter 23: Ellipse - §7                                   = $0c1c
.product3?Usage of product3:
Chapter 23: Ellipse - §7
Chapter 24: Maths routines - §5                                   = $0c1d
.product4?Usage of product4:
Chapter 24: Maths routines - §5                                   = $0c1e
.product5?Usage of product5:
Chapter 24: Maths routines - §5                                   = $0c1f

***** For square root *****
.sqrtResult0?Usage of sqrtResult0:
Chapter 16: Circle - §5
Chapter 24: Maths routines - §7                                = $0c17
.sqrtResult1?Usage of sqrtResult1:
Chapter 16: Circle - §5
Chapter 24: Maths routines - §7                                = $0c18
.sqrtResult2?Usage of sqrtResult2:
Chapter 24: Maths routines - §7                                = $0c19

.sqrtNumber0?Usage of sqrtNumber0:
Chapter 16: Circle - §4, §5
Chapter 23: Ellipse - §7
Chapter 24: Maths routines - §7                                = $0c1a     }
.sqrtNumber1?Usage of sqrtNumber1:
Chapter 16: Circle - §5
Chapter 23: Ellipse - §7
Chapter 24: Maths routines - §7                                = $0c1b     }
.sqrtNumber2?Usage of sqrtNumber2:
Chapter 16: Circle - §5
Chapter 23: Ellipse - §7
Chapter 24: Maths routines - §7                                = $0c1c     } 48 bit number to sqrt
.sqrtNumber3?Usage of sqrtNumber3:
Chapter 16: Circle - §5
Chapter 23: Ellipse - §7
Chapter 24: Maths routines - §7                                = $0c1d     }
.sqrtNumber4?Usage of sqrtNumber4:
Chapter 23: Ellipse - §7
Chapter 24: Maths routines - §6, §7                                = $0c1e     }
.sqrtNumber5?Usage of sqrtNumber5:
Chapter 23: Ellipse - §7
Chapter 24: Maths routines - §6, §7                                = $0c1f     }

.sqrtRemainder0?Usage of sqrtRemainder0:
Chapter 24: Maths routines - §7                             = $0c20
.sqrtRemainder1?Usage of sqrtRemainder1:
Chapter 24: Maths routines - §7                             = $0c21
.sqrtRemainder2?Usage of sqrtRemainder2:
Chapter 24: Maths routines - §7                             = $0c22
.sqrtRemainder3?Usage of sqrtRemainder3:
Chapter 24: Maths routines - §7                             = $0c23

.sqrtTemp0?Usage of sqrtTemp0:
Chapter 24: Maths routines - §7                                  = $0c24
.sqrtTemp1?Usage of sqrtTemp1:
Chapter 24: Maths routines - §7                                  = $0c25
.sqrtTemp2?Usage of sqrtTemp2:
Chapter 24: Maths routines - §7                                  = $0c26
.sqrtTemp3?Usage of sqrtTemp3:
Chapter 24: Maths routines - §7                                  = $0c27

$0c28-$0c2b [4 bytes] are not used

***** For division *****
.dividend0?Usage of dividend0:
Chapter 24: Maths routines - §1                                  = $0c2c
.dividend1?Usage of dividend1:
Chapter 24: Maths routines - §1                                  = $0c2d
.dividend2?Usage of dividend2:
Chapter 24: Maths routines - §1                                  = $0c2e

.divisor0?Usage of divisor0:
Chapter 24: Maths routines - §1                                   = $0c2f
.divisor1?Usage of divisor1:
Chapter 24: Maths routines - §1                                   = $0c30
.divisor2?Usage of divisor2:
Chapter 24: Maths routines - §1                                   = $0c31

.quotient0?Usage of quotient0:
Chapter 24: Maths routines - §1                                  = $0c32     24 bit quotient for divide
.quotient1?Usage of quotient1:
Chapter 24: Maths routines - §1                                  = $0c33     24 bit quotient for divide
.quotient2?Usage of quotient2:
Chapter 24: Maths routines - §1                                  = $0c34     24 bit quotient for divide

.divideTemp0?Usage of divideTemp0:
Chapter 24: Maths routines - §1                                = $0c35     temporary value during divide
.divideTemp1?Usage of divideTemp1:
Chapter 24: Maths routines - §1                                = $0c36     
.divideTemp2?Usage of divideTemp2:
Chapter 24: Maths routines - §1                                = $0c37     

***** For circle drawing *****
.circleTrackingLeftmostChordPoint?Usage of circleTrackingLeftmostChordPoint:
Chapter 16: Circle - §7, §8, §9, §19, §20           = $0c2c     index of the leftmost chord
                                                        point, or zero if we are not
                                                        tracking the chord
.circleTrackingSecondLineInQuadrant?Usage of circleTrackingSecondLineInQuadrant:
Chapter 16: Circle - §8, §19, §20         = $0c2d     index of the second line in the
                                                        quadrant, or zero if we are not
                                                        tracking
.circleRadialLine?Usage of circleRadialLine:
Chapter 16: Circle - §8, §19, §20                           = $0c2e     another temporary line index
.circleTrackingRightmostChordPoint?Usage of circleTrackingRightmostChordPoint:
Chapter 16: Circle - §7, §8, §9, §19          = $0c2f     index of the rightmost chord
                                                        point, or zero if we are not
                                                        tracking the chord

.circlePointXLow?Usage of circlePointXLow:
Chapter 16: Circle - §2, §5, §6, §7, §10                            = $0c30     
.circlePointXHigh?Usage of circlePointXHigh:
Chapter 16: Circle - §2, §3, §5, §6, §7, §8, §9, §10                           = $0c31     

.circlePointYLow?Usage of circlePointYLow:
Chapter 16: Circle - §2, §3, §5, §6, §7, §8, §9, §11, §12                            = $0c32     
.circlePointYHigh?Usage of circlePointYHigh:
Chapter 16: Circle - §2, §3, §5, §6, §7, §8, §9, §11, §12                           = $0c33     
.circleFillRowFlag?Usage of circleFillRowFlag:
Chapter 16: Circle - §3, §6, §8, §9                          = $0c34     set if we are on a new row to be
                                                        plotted, clear if just updating
                                                        position this time around the loop
.circlePixelShapeCurrentOffset?Usage of circlePixelShapeCurrentOffset:
Chapter 16: Circle - §5, §6              = $0c35     tracks offset within current pixel
                                                        shape when drawing circle (for
                                                        double width / height)


.circlePixelShapeForCurrentMODE?Usage of circlePixelShapeForCurrentMODE:
Chapter 16: Circle - §4, §5, §6             = $0c36     pixel shape:
                                                          bit 0 set = double width (MODE 2,5)
                                                          bit 1 set = half width   (MODE 0)

.circleSlopeTestLow?Usage of circleSlopeTestLow:
Chapter 16: Circle - §17                         = $0c37     
.circleSlopeTestMid1                        = $0c38     
.circleSlopeTestMid2                        = $0c39     
.circleSlopeTestHigh                        = $0c3a     

.circleRadiusSquaredLow?Usage of circleRadiusSquaredLow:
Chapter 16: Circle - §4, §5, §14                     = $0c37     
.circleRadiusSquaredMid1?Usage of circleRadiusSquaredMid1:
Chapter 16: Circle - §5                    = $0c38     
.circleRadiusSquaredMid2?Usage of circleRadiusSquaredMid2:
Chapter 16: Circle - §5                    = $0c39     
.circleRadiusSquaredHigh?Usage of circleRadiusSquaredHigh:
Chapter 16: Circle - §5                    = $0c3a     

.circleDiameterCountdownLow?Usage of circleDiameterCountdownLow:
Chapter 16: Circle - §5, §6                 = $0c3d     } counts down from (diameter-1) in
                                                        } steps of two
.circleDiameterCountdownHigh?Usage of circleDiameterCountdownHigh:
Chapter 16: Circle - §5, §6                = $0c3e     }

.circleDecisionLow?Usage of circleDecisionLow:
Chapter 16: Circle - §5, §6                          = $0c3f     } decision variable used in circle
                                                        } algorithm
.circleDecisionHigh?Usage of circleDecisionHigh:
Chapter 16: Circle - §5, §6                         = $0c40     }

.circleCountOddNumbersLow?Usage of circleCountOddNumbersLow:
Chapter 16: Circle - §5, §6                   = $0c41     } counts up from one in steps of two
.circleCountOddNumbersHigh?Usage of circleCountOddNumbersHigh:
Chapter 16: Circle - §5, §6                  = $0c42     }

.circleChordLine?Usage of circleChordLine:
Chapter 16: Circle - §7, §8, §9, §14, §15, §22, §25, §26                            = $0c43     offset of chord line variables from
                                                        .vduVariablesStart

.circleLine2Quadrant?Usage of circleLine2Quadrant:
Chapter 16: Circle - §14, §15, §17                        = $0c48
.circleLine3Quadrant?Usage of circleLine3Quadrant:
Chapter 16: Circle - §14, §15, §17                        = $0c49
.circleChordDestinationPoint?Usage of circleChordDestinationPoint:
Chapter 16: Circle - §14, §15, §22, §26                = $0c4a     end point of chord line
.circleQuadrants?Usage of circleQuadrants:
Chapter 16: Circle - §14, §17, §20, §22                            = $0c4b     [4 bytes] See
                                                        
                                                        .circleDoLineAndQuadrantInitialisation
.circleSecondaryLine?Usage of circleSecondaryLine:
Chapter 16: Circle - §20                        = $0c4f     if one line is in the quadrant, this
                                                        is the other line that may not be in
                                                        the quadrant
.circleCurrentQuadrant?Usage of circleCurrentQuadrant:
Chapter 16: Circle - §20, §22                      = $0c50     current quadrant
.circleQuadrantDataShifter?Usage of circleQuadrantDataShifter:
Chapter 16: Circle - §20, §21, §23, §24                  = $0c51     how many times to shift the quadrant
                                                        data when starting to track the chord
.circleFlag?Usage of circleFlag:
Chapter 16: Circle - §14, §22, §26                                 = $0c52

***** For ellipse drawing *****
.ellipseSignFlag?Usage of ellipseSignFlag:
Chapter 23: Ellipse - §5                            = $0c38     sign for shear

.ellipseAccumulatedShearLow?Usage of ellipseAccumulatedShearLow:
Chapter 23: Ellipse - §5, §7                 = $0c39     adds the shear value each row.
.ellipseAccumulatedShearMid?Usage of ellipseAccumulatedShearMid:
Chapter 23: Ellipse - §7                 = $0c3a     
.ellipseAccumulatedShearHigh?Usage of ellipseAccumulatedShearHigh:
Chapter 23: Ellipse - §7                = $0c3b     

.ellipseCountOddNumbersLow?Usage of ellipseCountOddNumbersLow:
Chapter 23: Ellipse - §5, §7                  = $0c3c     counts the odd numbers from 1
.ellipseCountOddNumbersMid1?Usage of ellipseCountOddNumbersMid1:
Chapter 23: Ellipse - §7                 = $0c3d     
.ellipseCountOddNumbersMid2?Usage of ellipseCountOddNumbersMid2:
Chapter 23: Ellipse - §7                 = $0c3e     
.ellipseCountOddNumbersHigh?Usage of ellipseCountOddNumbersHigh:
Chapter 23: Ellipse - §7                 = $0c3f     

.ellipseCountSquaresLow?Usage of ellipseCountSquaresLow:
Chapter 23: Ellipse - §7                     = $0c40     counts up in square numbers by
.ellipseCountSquaresMid1?Usage of ellipseCountSquaresMid1:
Chapter 23: Ellipse - §7                    = $0c41     adding next the odd number in
.ellipseCountSquaresMid2?Usage of ellipseCountSquaresMid2:
Chapter 23: Ellipse - §7                    = $0c42     sequence from 1.
.ellipseCountSquaresHigh?Usage of ellipseCountSquaresHigh:
Chapter 23: Ellipse - §7                    = $0c43     

.ellipseCountHeightLow?Usage of ellipseCountHeightLow:
Chapter 23: Ellipse - §3, §4, §5, §7, §8, §9                      = $0c44     loop counter
.ellipseCountHeightHigh?Usage of ellipseCountHeightHigh:
Chapter 23: Ellipse - §3, §4, §5, §7, §8, §9                     = $0c45     

.ellipseTempA?Usage of ellipseTempA:
Chapter 16: Circle - §14                               = $0c44     }
.ellipseTempB                               = $0c45     } temporary variables while drawing
.ellipseTempY?Usage of ellipseTempY:
Chapter 23: Ellipse - §8, §9                               = $0c46     } ellipse
.ellipseTempX?Usage of ellipseTempX:
Chapter 23: Ellipse - §8, §9                               = $0c47     }

§7. Extended Vector Table.

 To redirect the VDU vector to this GXR ROM we use the extended vector table (See NAUG p312)

.extendedVDUVLow?Usage of extendedVDUVLow:
Chapter 4: ROM header and service entry routines - §4
Chapter 8: Intercepting unknown VDU commands - §1                            = $0dd8     }
.extendedVDUVHigh?Usage of extendedVDUVHigh:
Chapter 4: ROM header and service entry routines - §4
Chapter 8: Intercepting unknown VDU commands - §1                           = $0dd9     } Extended vector table
.extendedVDUVROM?Usage of extendedVDUVROM:
Chapter 4: ROM header and service entry routines - §4
Chapter 8: Intercepting unknown VDU commands - §1                            = $0dda     }

This memory is a table indexed by ROM number. Each ROM gets one byte to store information.
We usually store the page number of the private workspace. During a reset, it stores 1
to indicate the GXR is becoming active, or 0 for inactive.
.romWorkspaceBytes?Usage of romWorkspaceBytes:
Chapter 4: ROM header and service entry routines - §3, §4
Chapter 5: Parsing star commands - §1
Chapter 6: Parsing OSBYTE (*FX) commands - §1, §5
Chapter 8: Intercepting unknown VDU commands - §2
Chapter 10: Star commands affecting memory - §2, §3                          = $0df0     ROM workspace bytes

§8. OS routines and tables.

 This ROM calls directly into the OS to perform functions, and also reads OS ROM based
 tables. Each machine has a different set of addresses.

!if (MACHINE = BBC_B) {
    .sixteenColourMODEMaskTable?Usage of sixteenColourMODEMaskTable:
Chapter 19: Rectangle copy and move - §10                         = $c407
    .gcolPlotOptionsTable?Usage of gcolPlotOptionsTable:
Chapter 12: VDU commands - §3
Chapter 19: Rectangle copy and move - §5                               = $c41c
    .twoColourMODEParameterTable?Usage of twoColourMODEParameterTable:
Chapter 12: VDU commands - §9                        = $c424
    .vdu22EntryPoint?Usage of vdu22EntryPoint:
Chapter 9: Trampoline code for OSWRCH - §1                                    = $c8eb
    .vdu25EntryPoint?Usage of vdu25EntryPoint:
Chapter 9: Trampoline code for OSWRCH - §1                                    = $c98c

    OS routine to swap two bytes in VDU variables (e.g. one 16 bit coordinate)
    On Entry:
          X is the offset to the first variable
          Y is the offset to the second variable
    .exchangeTwoVDUBytes?Usage of exchangeTwoVDUBytes:
Chapter 14: Point and Rectangle - §3
Chapter 17: Lines - §9
Chapter 19: Rectangle copy and move - §5                                = $cdde

    OS routine to plot a single point
    Given the current screen address details, renders the pixel by writing to the screen
    address, applying the colour masks and plot type.
    On Entry:
          Y is the vertical offset within the current cell
    .plotPointWithinBoundsAtY?Usage of plotPointWithinBoundsAtY:
Chapter 11: Shared PLOT subroutines and tables - §6
Chapter 17: Lines - §12
Chapter 18: Flood fill and horizontal fill - §10                           = $d0f3

    OS routine to check that the graphics point given by offset X is within the graphics
    window
    On Entry:
      X: offset to the point to check ('gpoint')
    On Exit:
      .vduTempStoreDA is zero if the gpoint is within the graphics window, or the four low
    bits
                   indicate which regions failed:
    
          %0000   success (gpoint is within window)
          %0001   gpoint X is left of  the left   edge of the graphics window
          %0010   gpoint X is right of the right  edge of the graphics window
          %0100   gpoint Y is below    the bottom edge of the graphics window
          %1000   gpoint Y is above    the top    edge of the graphics window
    .checkPointXIsWithinGraphicsWindow?Usage of checkPointXIsWithinGraphicsWindow:
Chapter 11: Shared PLOT subroutines and tables - §7
Chapter 17: Lines - §12
Chapter 20: Sprite plotting - §1
Chapter 21: Sprite commands - §4                  = $d10f

    OS routine to check coordinate of a point is in the window bounds (horizontal or
    vertical)
    On Entry:
          X is the offset to the coordinate to check minus two bytes
          Y is the offset to the second variable to check (0 for horizontal or 2 for
    vertical)
    On Exit:
          .vduTempStoreDA is the error code (0 = no error, 1 = first check failed, 2 =
    second check
          failed)
          Zero flag set if no error
    .checkPointIsWithinWindowHorizontalOrVertical?Usage of checkPointIsWithinWindowHorizontalOrVertical:
Chapter 19: Rectangle copy and move - §3       = $d128

    OS routine to convert external relative coordinates to pixels
    Convert pair of external coordinates to pixels (horizontal and vertical)
    On Entry:
          X is the offset in vdu variables to the coordinate to convert
    .plotConvertExternalRelativeCoordinatesToPixels?Usage of plotConvertExternalRelativeCoordinatesToPixels:
Chapter 12: VDU commands - §3     = $d14d

    Move graphics cursor up a cell
    .moveGraphicsCursorAddressUpOneCharacterCell?Usage of moveGraphicsCursorAddressUpOneCharacterCell:
Chapter 17: Lines - §12        = $d3d3

    OS routine to update the mask value, and move graphics cursor address on to next cell to
    the right
    On Entry:
          Carry always SET
    .moveGraphicsCursorAddressTotheRightAndUpdateMask?Usage of moveGraphicsCursorAddressTotheRightAndUpdateMask:
Chapter 17: Lines - §12
Chapter 18: Flood fill and horizontal fill - §8, §11   = $d3ed

    OS routine to move the graphics cursor address on to next cell to the right
    On Entry:
          Carry always SET
    .moveGraphicsCursorAddressTotheRight?Usage of moveGraphicsCursorAddressTotheRight:
Chapter 19: Rectangle copy and move - §5                = $d3f2

    OS routine to update the mask value, and move graphics cursor address on to previous
    cell to the left
    On Entry:
          Carry always SET
    .moveGraphicsCursorAddressTotheLeftAndUpdateMask?Usage of moveGraphicsCursorAddressTotheLeftAndUpdateMask:
Chapter 17: Lines - §12
Chapter 18: Flood fill and horizontal fill - §7
Chapter 20: Sprite plotting - §1
Chapter 21: Sprite commands - §4    = $d3fd

    OS routine to copy eight bytes (four coordinates) of VDU variables
    On Entry:
          X = source (offset from .vduVariablesStart)
          Y = destination (offset from .vduVariablesStart)
    .copyEightBytesWithinVDUVariables?Usage of copyEightBytesWithinVDUVariables:
Chapter 19: Rectangle copy and move - §5                   = $d47c

    OS routine to copy two bytes (one coordinate) of VDU variables
    On Entry:
          X = source (offset from .vduVariablesStart)
          Y = destination (offset from .vduVariablesStart)
    .copyTwoBytesWithinVDUVariables?Usage of copyTwoBytesWithinVDUVariables:
Chapter 14: Point and Rectangle - §4
Chapter 19: Rectangle copy and move - §5
Chapter 21: Sprite commands - §4
Chapter 23: Ellipse - §4, §5                     = $d482

    OS routine to copy four bytes of VDU variables
    On Entry:
          X = source (offset from .vduVariablesStart)
          Y = destination (offset from .vduVariablesStart)
    .copyFourBytesWithinVDUVariables?Usage of copyFourBytesWithinVDUVariables:
Chapter 16: Circle - §2, §3
Chapter 19: Rectangle copy and move - §5
Chapter 20: Sprite plotting - §1
Chapter 23: Ellipse - §7                    = $d48a

    OS routine to fill a single horizontal row of pixels
    Used as part of clearing the graphics window or filling a triangle.
    On Entry:
          X = offset into VDU variables for one extreme graphics pixel X coordinate
          Y = offset into VDU variables for the other extreme graphics pixel X coordinate
    .fillRow?Usage of fillRow:
Chapter 11: Shared PLOT subroutines and tables - §5                                            = $d6a6

    OS routine to set screen address
    On Entry:
          X is the vdu variables offset to the graphics point to check
    On Exit:
          .vduScreenAddressOfGraphicsCursorCellLow/High is the screen address
          Y is the vertical offset within the character cell (0-7)
          Preserves X
    .setScreenAddress?Usage of setScreenAddress:
Chapter 11: Shared PLOT subroutines and tables - §7
Chapter 20: Sprite plotting - §1
Chapter 21: Sprite commands - §4                                   = $d864
} else if (MACHINE = BBC_B_PLUS) {
    .sixteenColourMODEMaskTable                         = $c3fe
    .gcolPlotOptionsTable                               = $c413
    .twoColourMODEParameterTable                        = $c41b
    .vdu25EntryPoint                                    = $c939
    .vdu22EntryPoint                                    = $caee
    .exchangeTwoVDUBytes                                = $cda6
    .plotPointWithinBoundsAtY                           = $d0bf
    .checkPointXIsWithinGraphicsWindow                  = $ca79
    .checkPointIsWithinWindowHorizontalOrVertical       = $d0d9
    .plotConvertExternalRelativeCoordinatesToPixels     = $d0fe
    .moveGraphicsCursorAddressUpOneCharacterCell        = $d34b
    .moveGraphicsCursorAddressTotheRightAndUpdateMask   = $d365
    .moveGraphicsCursorAddressTotheRight                = $d36a
    .moveGraphicsCursorAddressTotheLeftAndUpdateMask    = $d375
    .copyEightBytesWithinVDUVariables                   = $d3f4
    .copyTwoBytesWithinVDUVariables                     = $d3fb
    .copyFourBytesWithinVDUVariables                    = $d403
    .fillRow                                            = $d62e
    .setScreenAddress                                   = $d7ed

    For the B+ we need to execute LDA (.vduScreenAddressOfGraphicsCursorCellLow),Y
                              and STA (.vduScreenAddressOfGraphicsCursorCellLow),Y
    from within the OS address space in order to access main or shadow RAM as appropriate.
    There isn't a bare LDA (.vduScreenAddressOfGraphicsCursorCellLow),Y:RTS we can use, so
    we do the best we can, which requires a bit of fiddling around in the GXR code compared
    to the model B case.
    .plotFast?Usage of plotFast:
Chapter 19: Rectangle copy and move - §5                                           = $d0cd write byte to screen
    .plotByte?Usage of plotByte:
Chapter 20: Sprite plotting - §1                                           = $d0d0 write byte to screen with
                                                                GCOL mode
    .checkPixelIsBackgroundColourFast?Usage of checkPixelIsBackgroundColourFast:
Chapter 18: Flood fill and horizontal fill - §14
Chapter 19: Rectangle copy and move - §5
Chapter 21: Sprite commands - §4                   = $d427 read byte from screen

    For reference, here is the relevant code from the B+ OS ROM:
    
          .plotFast
    d0cd      STA (.vduScreenAddressOfGraphicsCursorCellLow),Y    ; put it back again
    d0cf      RTS                                                 ;
    
          .plotByte
    d0d0      LDA (.vduScreenAddressOfGraphicsCursorCellLow),Y    ;
    d0d2      ORA .vduGraphicsColourByteOR                        ;
    d0d4      EOR .vduGraphicsColourByteEOR                       ;
    d0d6      STA (.vduScreenAddressOfGraphicsCursorCellLow),Y    ;
    d0d8      RTS                                                 ;
    ...
          .checkPixelIsBackgroundColourFast
    d427      LDA (.vduScreenAddressOfGraphicsCursorCellLow),Y    ; get byte from current
    graphics
    d429      EOR .vduBackgroundGraphicsColour                    ; cell, compare with
    current
    d42c      STA .vduTempStoreDA                                 ; background colour and
    store it
    d42e      RTS                                                 ;

} else if (MACHINE = ELECTRON) {
    .sixteenColourMODEMaskTable                         = $c3c2
    .gcolPlotOptionsTable                               = $c3d7
    .twoColourMODEParameterTable                        = $c3df
    .vdu25EntryPoint                                    = $c986
    .vdu22EntryPoint                                    = $c8ec
    .exchangeTwoVDUBytes                                = $cd1a
    .plotPointWithinBoundsAtY                           = $d004
    .checkPointXIsWithinGraphicsWindow                  = $d020
    .checkPointIsWithinWindowHorizontalOrVertical       = $d039
    .plotConvertExternalRelativeCoordinatesToPixels     = $d05e
    .moveGraphicsCursorAddressUpOneCharacterCell        = $d2ea
    .moveGraphicsCursorAddressTotheRightAndUpdateMask   = $d304
    .moveGraphicsCursorAddressTotheRight                = $d309
    .moveGraphicsCursorAddressTotheLeftAndUpdateMask    = $d314
    .copyEightBytesWithinVDUVariables                   = $d393
    .copyTwoBytesWithinVDUVariables                     = $d399
    .copyFourBytesWithinVDUVariables                    = $d3a1
    .fillRow                                            = $d5bc
    .setScreenAddress                                   = $d77a
    .selectRom?Usage of selectRom:
Chapter 9: Trampoline code for OSWRCH - §2                                          = $e3a0
} else {
    +unknown_machine
}

§9. romSelectRegister.

.romSelectRegister?Usage of romSelectRegister:
Chapter 9: Trampoline code for OSWRCH - §2                          = $fe30

§10. extendedVectorTableVDUV.

.extendedVectorTableVDUV?Usage of extendedVectorTableVDUV:
Chapter 4: ROM header and service entry routines - §4                    = $ff39

§11. Regular OS entry points.

.OSFIND?Usage of OSFIND:
Chapter 21: Sprite commands - §11                                     = $ffce
.OSBGET?Usage of OSBGET:
Chapter 21: Sprite commands - §11                                     = $ffd7
.OSARGS?Usage of OSARGS:
Chapter 21: Sprite commands - §13                                     = $ffda
.OSFILE?Usage of OSFILE:
Chapter 2: Constants - §3
Chapter 21: Sprite commands - §7, §11                                     = $ffdd
.OSRDCH?Usage of OSRDCH:
Chapter 22: Sprite Editor - §22                                     = $ffe0
.OSNEWL?Usage of OSNEWL:
Chapter 7: Parsing *HELP Commands - §1, §5                                     = $ffe7
.OSWRCH?Usage of OSWRCH:
§2
Chapter 4: ROM header and service entry routines - §4
Chapter 7: Parsing *HELP Commands - §1, §5
Chapter 9: Trampoline code for OSWRCH - §1
Chapter 21: Sprite commands - §1
Chapter 22: Sprite Editor - §9, §10, §11, §23, §65, §82, §83, §84, §85, §87, §89                                     = $ffee
.OSBYTE?Usage of OSBYTE:
§2
Chapter 4: ROM header and service entry routines - §2, §4
Chapter 6: Parsing OSBYTE (*FX) commands - §1, §2, §4, §5
Chapter 10: Star commands affecting memory - §1, §2
Chapter 21: Sprite commands - §13
Chapter 22: Sprite Editor - §22, §23, §56                                     = $fff4