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63 lines
2.0 KiB
ArmAsm
63 lines
2.0 KiB
ArmAsm
; ---------------------------------------------------------------------------
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; crt0.s
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; ---------------------------------------------------------------------------
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;
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; Startup code for Ohio Scientific Challenger 1P
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.export _init, _exit
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.import _main
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.export __STARTUP__ : absolute = 1 ; Mark as startup
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.import __RAM_START__, __RAM_SIZE__ ; Linker generated
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.import zerobss, initlib, donelib
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.include "zeropage.inc"
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.include "extzp.inc"
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; ---------------------------------------------------------------------------
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; Place the startup code in a special segment
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.segment "STARTUP"
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; ---------------------------------------------------------------------------
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; A little light 6502 housekeeping
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_init: ldx #$FF ; Initialize stack pointer to $01FF
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txs
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cld ; Clear decimal mode
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; ---------------------------------------------------------------------------
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; Initialize screen width
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; TODO: Can initialization be done in a more idiomatic way?
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; TODO: Create function for changing screen width
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lda #$18
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sta SCR_LINELEN
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; ---------------------------------------------------------------------------
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; Set cc65 argument stack pointer
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lda #<(__RAM_START__ + __RAM_SIZE__)
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sta sp
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lda #>(__RAM_START__ + __RAM_SIZE__)
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sta sp+1
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; ---------------------------------------------------------------------------
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; Initialize memory storage
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; copydata seems to be only necessary for special systems
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jsr zerobss ; Clear BSS segment
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; jsr copydata ; Initialize DATA segment
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jsr initlib ; Run constructors
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; ---------------------------------------------------------------------------
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; Call main()
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jsr _main
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; ---------------------------------------------------------------------------
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; Back from main (this is also the _exit entry): force a software break
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_exit: jsr donelib ; Run destructors
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brk
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