Constants used by the ROM

• §1. Hardware
• §2. Characters
• §3. Offsets into the private workspace
• §4. Sprites are stored (in memory and on disk) with a six byte header

§1. Hardware.

 The Electron version is courtesy of SteveF on the Stardot forum (aka ZornsLemma on GitHub).
     see https://stardot.org.uk/forums/viewtopic.php?p=295211#p295211 and
     see https://github.com/ZornsLemma/GXR

!macro unknown_machine {
    !error "Unknown machine"
}

Use these numbers on the acme command line with -D to define the MACHINE to assemble for.
BBC_B       = 1000
BBC_B_PLUS  = 1001
ELECTRON    = 1002

Set version strings based on the machine we are assembling for.
!if MACHINE = BBC_B {
    .version?Usage of version:
Chapter 4: ROM header and service entry routines - §1
Chapter 10: Star commands affecting memory - §1
Chapter 24: Maths routines - §7     = "1.20"
    .fullVersion?Usage of fullVersion:
Chapter 4: ROM header and service entry routines - §1 = "1.20"
} else if MACHINE = BBC_B_PLUS {
    .version     = "2.00"
    .fullVersion = "2.00"
} else if MACHINE = ELECTRON {
    .version     = "1.00"
    .fullVersion = "1.00a"
} else {
    +unknown_machine
}

§2. Characters.

.charLF?Usage of charLF:
Chapter 4: ROM header and service entry routines - §1
Chapter 7: Parsing *HELP Commands - §1
Chapter 22: Sprite Editor - §87                                     = $0A       
.charCR?Usage of charCR:
Chapter 4: ROM header and service entry routines - §1
Chapter 7: Parsing *HELP Commands - §1, §5
Chapter 22: Sprite Editor - §87                                     = $0D       
.charDefineTextColour?Usage of charDefineTextColour:
Chapter 22: Sprite Editor - §87                       = $11       
.charHomeCursor?Usage of charHomeCursor:
Chapter 22: Sprite Editor - §87                             = $1E       
.charMoveCursor?Usage of charMoveCursor:
Chapter 22: Sprite Editor - §87                             = $1F       

§3. Offsets into the private workspace.

 The GXR ROM uses the first page of its private workspace to store variables. These constants are
 offsets from the start of the ROM's private workspace.

 The first 72 bytes ($00-$47) contain the code for intercepting OSWRCH, checking for VDU 22 and
 VDU 25 and switching in the ROM and calling into it. The next 81 bytes ($48-$98) are for the
 variables listed below. The remaining 103 bytes ($99-$ff) are used to cache the 'soft character
 definitions' (from $0c00-$0c66) temporarily while a PLOT routine is executing. The soft character
 definitions are reinstated either at the end of the PLOT routine, or on a reset when the ROM
 re-initialises itself (checks for flag .workspaceOffsetHasCachedSoftCharacterDefinitions).

.workspaceOffsetTotalPagesWithoutSprites?Usage of workspaceOffsetTotalPagesWithoutSprites:
Chapter 4: ROM header and service entry routines - §4
Chapter 10: Star commands affecting memory - §4, §5    = $48       1 or 3 pages, depending if *FLOOD is
                                                        enabled
.workspaceOffsetOptions?Usage of workspaceOffsetOptions:
Chapter 4: ROM header and service entry routines - §4
Chapter 6: Parsing OSBYTE (*FX) commands - §2
Chapter 7: Parsing *HELP Commands - §1
Chapter 10: Star commands affecting memory - §4, §5, §6
Chapter 18: Flood fill and horizontal fill - §3
Chapter 22: Sprite Editor - §22, §28, §58, §87                     = $49       bit 7 = flood fill enabled, bit 6 =
                                                        flood pending, bit 0=pen up/down in
                                                        sprite editor
.workspaceOffsetSpritePages?Usage of workspaceOffsetSpritePages:
Chapter 4: ROM header and service entry routines - §4
Chapter 5: Parsing star commands - §1
Chapter 6: Parsing OSBYTE (*FX) commands - §2
Chapter 7: Parsing *HELP Commands - §1
Chapter 10: Star commands affecting memory - §5, §6
Chapter 21: Sprite commands - §4, §16                 = $4a       number of pages reserved for sprites
.workspaceOffsetNumberOfSprites?Usage of workspaceOffsetNumberOfSprites:
Chapter 4: ROM header and service entry routines - §4
Chapter 7: Parsing *HELP Commands - §1
Chapter 10: Star commands affecting memory - §7
Chapter 21: Sprite commands - §7, §8
Chapter 22: Sprite Editor - §17, §18, §21, §76, §78             = $4b       
.workspaceOffsetCurrentSpriteAddressLow?Usage of workspaceOffsetCurrentSpriteAddressLow:
Chapter 6: Parsing OSBYTE (*FX) commands - §3
Chapter 10: Star commands affecting memory - §7
Chapter 20: Sprite plotting - §1
Chapter 21: Sprite commands - §16
Chapter 22: Sprite Editor - §19     = $4c       
.workspaceOffsetCurrentSpriteAddressHigh    = $4d       
.workspaceOffsetSpriteStartPage?Usage of workspaceOffsetSpriteStartPage:
Chapter 4: ROM header and service entry routines - §4
Chapter 10: Star commands affecting memory - §5
Chapter 21: Sprite commands - §7, §8
Chapter 22: Sprite Editor - §76, §78             = $4e       the first page of the sprite data.
.workspaceOffsetSpriteEndPage?Usage of workspaceOffsetSpriteEndPage:
Chapter 4: ROM header and service entry routines - §4
Chapter 21: Sprite commands - §11
Chapter 22: Sprite Editor - §22, §78               = $4f       the page after the sprite data.
.workspaceOffsetChosenSpriteAddressLow?Usage of workspaceOffsetChosenSpriteAddressLow:
Chapter 4: ROM header and service entry routines - §4
Chapter 22: Sprite Editor - §49      = $50       
.workspaceOffsetChosenSpriteAddressHigh     = $51       
.workspaceOffsetChosenSpriteIndex?Usage of workspaceOffsetChosenSpriteIndex:
Chapter 4: ROM header and service entry routines - §4
Chapter 22: Sprite Editor - §48, §49           = $52       

OSFILE parameter block (used when loading and saving sprite data)
.workspaceOffsetParamBlock?Usage of workspaceOffsetParamBlock:
Chapter 21: Sprite commands - §7, §11                  = $53       
.workspaceOffsetFilenameLow?Usage of workspaceOffsetFilenameLow:
Chapter 21: Sprite commands - §7, §11                 = $53       
.workspaceOffsetFilenameHigh?Usage of workspaceOffsetFilenameHigh:
Chapter 21: Sprite commands - §7, §11                = $54       
.workspaceOffsetLoadAddressLow?Usage of workspaceOffsetLoadAddressLow:
Chapter 21: Sprite commands - §11              = $55       
.workspaceOffsetLoadAddressMid1             = $56       
.workspaceOffsetLoadAddressMid2             = $57       
.workspaceOffsetLoadAddressHigh             = $58       
.workspaceOffsetExecAddressLow?Usage of workspaceOffsetExecAddressLow:
Chapter 21: Sprite commands - §11              = $59       
.workspaceOffsetExecAddressMid1             = $5a       
.workspaceOffsetExecAddressMid2             = $5b       
.workspaceOffsetExecAddressHigh             = $5c       
.workspaceOffsetStartAddressLow?Usage of workspaceOffsetStartAddressLow:
Chapter 21: Sprite commands - §7             = $5d       
.workspaceOffsetStartAddressMid1?Usage of workspaceOffsetStartAddressMid1:
Chapter 21: Sprite commands - §7            = $5e       
.workspaceOffsetStartAddressMid2?Usage of workspaceOffsetStartAddressMid2:
Chapter 21: Sprite commands - §7            = $5f       
.workspaceOffsetStartAddressHigh            = $60       
.workspaceOffsetEndAddressLow?Usage of workspaceOffsetEndAddressLow:
Chapter 21: Sprite commands - §7               = $61       
.workspaceOffsetEndAddressMid1?Usage of workspaceOffsetEndAddressMid1:
Chapter 21: Sprite commands - §7              = $62       
.workspaceOffsetEndAddressMid2              = $63       
.workspaceOffsetEndAddressHigh              = $64       
.workspaceOffsetEndOfSpritesAddressLow?Usage of workspaceOffsetEndOfSpritesAddressLow:
Chapter 21: Sprite commands - §11      = $65       
.workspaceOffsetEndOfSpritesAddressHigh?Usage of workspaceOffsetEndOfSpritesAddressHigh:
Chapter 21: Sprite commands - §11     = $66       

.workspaceOffsetOldVDUVectorVLow?Usage of workspaceOffsetOldVDUVectorVLow:
Chapter 8: Intercepting unknown VDU commands - §1            = $67       }
.workspaceOffsetOldVDUVectorVHigh           = $68       } old VDU Vector

.workspaceOffsetOldExtendedVDUVLow          = $69       }
.workspaceOffsetOldExtendedVDUVHigh         = $6a       } old extended vector
.workspaceOffsetOldExtendedVDUVROM?Usage of workspaceOffsetOldExtendedVDUVROM:
Chapter 8: Intercepting unknown VDU commands - §1          = $6b       } (see
                                                        } .swapWorkspaceWithVDUVectors)

.workspaceOffsetCurrentPatterns?Usage of workspaceOffsetCurrentPatterns:
Chapter 12: VDU commands - §3, §7, §8, §9
Chapter 14: Point and Rectangle - §5             = $6c       [32 bytes]

The four patterns are stored at $6c to $8b (four patterns of 8 bytes each = 32 bytes)

pattern 1         = workspace[$6c to $73]
pattern 2         = workspace[$74 to $7b]
pattern 3         = workspace[$7c to $83]
pattern 4         = workspace[$84 to $8b]

.workspaceOffsetDotDashPattern?Usage of workspaceOffsetDotDashPattern:
Chapter 6: Parsing OSBYTE (*FX) commands - §6              = $8c       dot-dash pattern [8 bytes]

.workspaceOffsetDotDashRepeatLength?Usage of workspaceOffsetDotDashRepeatLength:
Chapter 6: Parsing OSBYTE (*FX) commands - §2, §7
Chapter 12: VDU commands - §7         = $94       pattern length in bits

Dot-dash pattern state
.workspaceOffsetDotDashBitsRemaining        = $95       current remaining bits of pattern
.workspaceOffsetDotDashBit                  = $96       current bit within current byte
.workspaceOffsetDotDashPatternByte?Usage of workspaceOffsetDotDashPatternByte:
Chapter 17: Lines - §16, §17          = $97       current byte

.workspaceOffsetHasCachedSoftCharacterDefinitions?Usage of workspaceOffsetHasCachedSoftCharacterDefinitions:
Chapter 4: ROM header and service entry routines - §4
Chapter 12: VDU commands - §3, §4 = $98 set to $80 if soft character
                                                        definitions have been cached into
                                                        workspace, otherwise $00.
.workspaceOffsetSoftFontCache?Usage of workspaceOffsetSoftFontCache:
Chapter 12: VDU commands - §3, §4               = $99       copy of some soft character
                                                        definitions while PLOTting
                                                        [$67 bytes, i.e. to end of page]

§4. Sprites are stored (in memory and on disk) with a six byte header.

   0: width - 1
   1: height - 1
   2: } size in bytes of the sprite data (without the six byte header)
   3: }
   4: MODE in which the sprite was defined
   5: sprite number

.spriteHeaderOffsetWidth?Usage of spriteHeaderOffsetWidth:
Chapter 6: Parsing OSBYTE (*FX) commands - §3
Chapter 22: Sprite Editor - §12, §22, §43, §50, §52, §54, §59, §60, §64, §66, §67, §70, §71                    = 0
.spriteHeaderOffsetHeight?Usage of spriteHeaderOffsetHeight:
Chapter 22: Sprite Editor - §39, §46, §47, §50, §52, §53, §54, §59, §63, §64, §66, §70, §71                   = 1
.spriteHeaderOffsetSizeInBytesLow?Usage of spriteHeaderOffsetSizeInBytesLow:
Chapter 21: Sprite commands - §4
Chapter 22: Sprite Editor - §12, §17, §18, §21, §55           = 2
.spriteHeaderOffsetSizeInBytesHigh?Usage of spriteHeaderOffsetSizeInBytesHigh:
Chapter 21: Sprite commands - §4
Chapter 22: Sprite Editor - §12, §17, §55          = 3
.spriteHeaderOffsetModeNumber?Usage of spriteHeaderOffsetModeNumber:
Chapter 21: Sprite commands - §4
Chapter 22: Sprite Editor - §22               = 4
.spriteHeaderOffsetSpriteNumber?Usage of spriteHeaderOffsetSpriteNumber:
Chapter 21: Sprite commands - §4, §17
Chapter 22: Sprite Editor - §18, §22, §23             = 5