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cc65/libsrc/vic20/crt0.s
uz 8216bf1d6a Force an import of the special symbol __STARTUP__ in the C compiler when
main() is encountered. Define this symbol in the startup code. This will
automatically force linking of the startup code which can then reside inside
the standard library as any other object file.


git-svn-id: svn://svn.cc65.org/cc65/trunk@3988 b7a2c559-68d2-44c3-8de9-860c34a00d81
2009-07-31 12:05:42 +00:00

152 lines
3.1 KiB
ArmAsm

;
; Startup code for cc65 (Vic20 version)
;
.export _exit
.export __STARTUP__ : absolute = 1 ; Mark as startup
.import initlib, donelib, callirq
.import zerobss, push0
.import callmain
.import RESTOR, BSOUT, CLRCH
.import __INTERRUPTOR_COUNT__
.import __RAM_START__, __RAM_SIZE__ ; Linker generated
.include "zeropage.inc"
.include "vic20.inc"
; ------------------------------------------------------------------------
; Place the startup code in a special segment.
.segment "STARTUP"
; BASIC header with a SYS call
.word Head ; Load address
Head: .word @Next
.word .version ; Line number
.byte $9E ; SYS token
.byte <(((@Start / 1000) .mod 10) + $30)
.byte <(((@Start / 100) .mod 10) + $30)
.byte <(((@Start / 10) .mod 10) + $30)
.byte <(((@Start / 1) .mod 10) + $30)
.byte $00 ; End of BASIC line
@Next: .word 0 ; BASIC end marker
@Start:
; ------------------------------------------------------------------------
; Actual code
ldx #zpspace-1
L1: lda sp,x
sta zpsave,x ; Save the zero page locations we need
dex
bpl L1
; Close open files
jsr CLRCH
; Switch to second charset
lda #14
jsr BSOUT
; Clear the BSS data
jsr zerobss
; Save system stuff and setup the stack
tsx
stx spsave ; Save the system stack ptr
lda #<(__RAM_START__ + __RAM_SIZE__)
sta sp
lda #>(__RAM_START__ + __RAM_SIZE__)
sta sp+1 ; Set argument stack ptr
; If we have IRQ functions, chain our stub into the IRQ vector
lda #<__INTERRUPTOR_COUNT__
beq NoIRQ1
lda IRQVec
ldx IRQVec+1
sta IRQInd+1
stx IRQInd+2
lda #<IRQStub
ldx #>IRQStub
sei
sta IRQVec
stx IRQVec+1
cli
; Call module constructors
NoIRQ1: jsr initlib
; Push arguments and call main()
jsr callmain
; Back from main (This is also the _exit entry). Run module destructors
_exit: jsr donelib
; Reset the IRQ vector if we chained it.
pha ; Save the return code on stack
lda #<__INTERRUPTOR_COUNT__
beq NoIRQ2
lda IRQInd+1
ldx IRQInd+2
sei
sta IRQVec
stx IRQVec+1
cli
; Copy back the zero page stuff
NoIRQ2: ldx #zpspace-1
L2: lda zpsave,x
sta sp,x
dex
bpl L2
; Place the program return code into ST
pla
sta ST
; Restore the stack pointer
ldx spsave
txs
; Reset changed vectors, back to basic
jmp RESTOR
; ------------------------------------------------------------------------
; The IRQ vector jumps here, if condes routines are defined with type 2.
IRQStub:
cld ; Just to be sure
jsr callirq ; Call the functions
jmp IRQInd ; Jump to the saved IRQ vector
; ------------------------------------------------------------------------
; Data
.data
IRQInd: jmp $0000
.segment "ZPSAVE"
zpsave: .res zpspace
.bss
spsave: .res 1