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88 lines
1.3 KiB
NASM
88 lines
1.3 KiB
NASM
; *** Variables ***
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; Value of `SP` when basic was first invoked. This is where SP is going back to
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; on restarts.
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.equ BAS_INITSP BAS_RAMSTART
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; **Pointer** to current line number
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.equ BAS_PCURLN @+2
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.equ BAS_RAMEND @+2
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; *** Code ***
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basStart:
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ld (BAS_INITSP), sp
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xor a
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ld hl, .welcome
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call printstr
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call printcrlf
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ld hl, .welcome+2 ; points to a zero word
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ld (BAS_PCURLN), hl
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jr basPrompt
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.welcome:
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.db "OK", 0, 0
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basPrompt:
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ld hl, .sPrompt
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call printstr
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call stdioReadLine
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call parseDecimal
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jr z, .number
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call basDirect
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jr basPrompt
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.number:
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; do nothing for now, we only support direct mode.
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ld hl, .sNumber
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call basPrintLn
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jr basPrompt
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.sNumber:
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.db "A number!", 0
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.sPrompt:
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.db "> ", 0
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basDirect:
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ex de, hl
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ld hl, basCmds1
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.loop:
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ld a, 4
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call strncmp
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jr z, .found
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ld a, 6
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call addHL
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ld a, (hl)
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cp 0xff
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jr nz, .loop
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ld hl, .sUnknown
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jr basPrintLn
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.found:
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inc hl \ inc hl \ inc hl \ inc hl
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call intoHL
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jp (hl)
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.sUnknown:
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.db "Unknown command", 0
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basPrintLn:
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call printcrlf
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call printstr
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jp printcrlf
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; *** Commands ***
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basBYE:
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ld hl, .sBye
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call basPrintLn
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; To quit the loop, let's return the stack to its initial value and
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; then return.
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xor a
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ld sp, (BAS_INITSP)
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ret
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.sBye:
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.db "Goodbye!", 0
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; direct only
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basCmds1:
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.db "bye", 0
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.dw basBYE
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; statements
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basCmds2:
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.db 0xff ; end of table
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