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https://github.com/sehugg/8bitworkshop.git
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96 lines
1.5 KiB
ArmAsm
96 lines
1.5 KiB
ArmAsm
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.module biosasm
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.globl _STIMER,_CTIMER,_BIGFONT,_SMLFONT
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.area BIOSSTART (ABS)
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.org 0x0
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BIOSStart:
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di ; disable interrupts
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ld HL,#0x2000
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ld A,(HL) ; A <- mem[0x2000]
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cp #0x55 ; found sentinel byte? ($55)
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jp Z,FoundSentinel ; yes, load program
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.if 1
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jp 0x2000 ; jump to $2000
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.else
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jp _main ; jump to test program
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.endif
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FoundSentinel:
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ld SP,#0x4fce ; position stack below BIOS vars
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call _bios_init ; misc. bios init routines
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ld HL,#0x2005 ; cartridge start vector
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ld A,(HL)
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inc HL
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ld H,(HL)
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ld L,A
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jp (HL) ; jump to cart start vector
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SYSCALL38:
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.org 0x38
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push hl
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push af
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push bc
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push de
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push ix
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push iy
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ld hl,#0
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add hl,sp
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push hl ; HL points to context block
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call _SYSCALL ; syscall handler
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pop hl
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pop iy
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pop ix
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pop de
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pop bc
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pop af
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pop hl
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ret
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DOPEVector:
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.org 0x200
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JP _STIMER
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JP _CTIMER
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.db 0x20, 8, 8, 1, 7 ; Font descriptor (big font)
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.dw _BIGFONT
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.db 0xa0, 4, 6, 1, 5 ; Font descriptor (small font)
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.dw _SMLFONT
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ReloadRegs:
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ld c,(hl)
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inc hl
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ld b,(hl)
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inc hl
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push bc
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pop iy
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ld c,(hl)
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inc hl
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ld b,(hl)
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inc hl
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push bc
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pop ix
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ld c,(hl)
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inc hl
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ld b,(hl)
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inc hl
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push bc
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pop de
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ld c,(hl)
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inc hl
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ld b,(hl)
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inc hl
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push bc
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ld c,(hl)
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inc hl
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ld b,(hl)
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inc hl
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push bc
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pop af
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ld c,(hl)
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inc hl
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ld b,(hl)
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inc hl
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push bc
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pop hl
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pop bc
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ret
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