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Update bootstrap code

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Was missing some things like initializing the stack pointer, clearing
BSS, and things like that
This commit is contained in:
Byron Lathi
2022-03-11 22:57:22 -06:00
parent 3d9d340520
commit 5106e50395
2 changed files with 58 additions and 14 deletions
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70
sw/boot.s
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@@ -1,15 +1,59 @@
.import _main ; ---------------------------------------------------------------------------
; crt0.s
.export __STARTUP__ : absolute = 1 ; ---------------------------------------------------------------------------
;
; Startup code for cc65 (Single Board Computer version)
.segment "VECTORS" .export _init, _exit
.import _main
.addr _init
.addr _init
.addr _init
.segment "STARTUP"
_init: jsr _main
end: jmp end .export __STARTUP__ : absolute = 1 ; Mark as startup
.import __RAM_START__, __RAM_SIZE__ ; Linker generated
.import copydata, zerobss, initlib, donelib
.include "zeropage.inc"
.segment "VECTORS"
.addr _init
.addr _init
.addr _init
; ---------------------------------------------------------------------------
; Place the startup code in a special segment
.segment "STARTUP"
; ---------------------------------------------------------------------------
; A little light 6502 housekeeping
_init: LDX #$FF ; Initialize stack pointer to $01FF
TXS
CLD ; Clear decimal mode
; ---------------------------------------------------------------------------
; Set cc65 argument stack pointer
LDA #<(__RAM_START__ + __RAM_SIZE__)
STA sp
LDA #>(__RAM_START__ + __RAM_SIZE__)
STA sp+1
; ---------------------------------------------------------------------------
; Initialize memory storage
JSR zerobss ; Clear BSS segment
JSR copydata ; Initialize DATA segment
JSR initlib ; Run constructors
; ---------------------------------------------------------------------------
; Call main()
JSR _main
; ---------------------------------------------------------------------------
; Back from main (this is also the _exit entry): force a software break
_exit: JSR donelib ; Run destructors
BRK

2
sw/main.c
View File

@@ -6,6 +6,6 @@ int main() {
uint16_t* seven_seg; uint16_t* seven_seg;
seven_seg = (uint16_t*)SEVEN_SEG; seven_seg = (uint16_t*)SEVEN_SEG;
*seven_seg = 0xa5a5; *seven_seg = 0xbabe;
return 0; return 0;
} }