bslathi19/super6502
1
0
Fork 0
Code Issues Pull Requests Actions Packages Projects Releases Wiki Activity

Update bootstrap code

Browse Source 
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
Download Patch File Download Diff File Expand all files Collapse all files

50
sw/boot.s
View File

@@ -1,6 +1,18 @@
; ---------------------------------------------------------------------------
; crt0.s
; ---------------------------------------------------------------------------
;
; Startup code for cc65 (Single Board Computer version)
.export _init, _exit
.import _main
.export __STARTUP__ : absolute = 1
.export __STARTUP__ : absolute = 1 ; Mark as startup
.import __RAM_START__, __RAM_SIZE__ ; Linker generated
.import copydata, zerobss, initlib, donelib
.include "zeropage.inc"
.segment "VECTORS"
@@ -8,8 +20,40 @@
.addr _init
.addr _init
; ---------------------------------------------------------------------------
; Place the startup code in a special segment
.segment "STARTUP"
_init: jsr _main
; ---------------------------------------------------------------------------
; A little light 6502 housekeeping
end: jmp end
_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;
seven_seg = (uint16_t*)SEVEN_SEG;
*seven_seg = 0xa5a5;
*seven_seg = 0xbabe;
return 0;
}