1
0
mirror of https://github.com/cc65/cc65.git synced 2024-12-23 19:29:37 +00:00
cc65/libsrc/c128/crt0.s

227 lines
5.2 KiB
ArmAsm
Raw Normal View History

;
; Startup code for cc65 (C128 version)
;
; This must be the *first* file on the linker command line
;
.export _exit
.export BRKStub, BRKOld, BRKInd
.import condes, initlib, donelib
.import initconio, doneconio, zerobss
.import push0, _main
.import __IRQFUNC_TABLE__, __IRQFUNC_COUNT__
.import __RAM_START__, __RAM_SIZE__
.include "c128.inc"
.include "../cbm/cbm.inc"
; ------------------------------------------------------------------------
; Constants
CC65_MMU_CFG = $0E ; Bank 0 with kernal ROM
IRQInd = $2FD ; JMP $0000 - used as indirect IRQ vector
; ------------------------------------------------------------------------
; Define and export the ZP variables for the C64 runtime
.exportzp sp, sreg, regsave
.exportzp ptr1, ptr2, ptr3, ptr4
.exportzp tmp1, tmp2, tmp3, tmp4
.exportzp regbank, zpspace
.zeropage
zpstart = *
sp: .res 2 ; Stack pointer
sreg: .res 2 ; Secondary register/high 16 bit for longs
regsave: .res 2 ; slot to save/restore (E)AX into
ptr1: .res 2
ptr2: .res 2
ptr3: .res 2
ptr4: .res 2
tmp1: .res 1
tmp2: .res 1
tmp3: .res 1
tmp4: .res 1
regbank: .res 6 ; 6 byte register bank
zpspace = * - zpstart ; Zero page space allocated
.code
; ------------------------------------------------------------------------
; BASIC header with a SYS call
.org $1BFF
.word Head ; Load address
Head: .word @Next
.word 1000 ; Line number
.byte $9E,"7181" ; SYS 7181
.byte $00 ; End of BASIC line
@Next: .word 0 ; BASIC end marker
.reloc
; ------------------------------------------------------------------------
; 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
; Get the current MMU setting and save it. Set new memory config.
lda MMU_CR ; Get current memory configuration...
pha ; ...and save it for later
lda #CC65_MMU_CFG ; Bank0 with kernal ROM
sta MMU_CR
; Clear the BSS data
jsr zerobss
; Save system stuff and setup the stack
pla ; Get MMU setting
sta mmusave
tsx
stx spsave ; save system stk ptr
lda #<(__RAM_START__ + __RAM_SIZE__)
sta sp
lda #>(__RAM_START__ + __RAM_SIZE__)
sta sp+1 ; Set argument stack ptr
; Call module constructors
jsr initlib
; Initialize conio stuff
jsr initconio
; If we have IRQ functions, chain our stub into the IRQ vector
lda #<__IRQFUNC_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
; Pass an empty command line
NoIRQ1: jsr push0 ; argc
jsr push0 ; argv
ldy #4 ; Argument size
jsr _main ; call the users code
; This is also the _exit entry. Reset the IRQ vector if we chained it.
_exit: lda #<__IRQFUNC_COUNT__
beq NoIRQ2
lda IRQInd+1
ldx IRQInd+2
sei
sta IRQVec
stx IRQVec+1
cli
; Run module destructors
NoIRQ2: jsr donelib
; Reset the conio stuff
jsr doneconio
; Reset stack and the MMU
ldx spsave
txs
lda mmusave
sta MMU_CR
; Copy back the zero page stuff
ldx #zpspace-1
L2: lda zpsave,x
sta sp,x
dex
bpl L2
; Done
jmp RESTOR
; ------------------------------------------------------------------------
; The C128 has ROM parallel to the RAM starting from $4000. The startup code
; above will change this setting so that we have RAM from $0000-$BFFF. This
; works quite well with the exception of interrupts: The interrupt handler
; is in ROM, and the ROM switches back to the ROM configuration, which means
; that parts of our program may not be accessible. Since the crt0 module is
; the first module in the program, it will always be below $4000 and always
; in RAM. So we place several short stubs here that switch back our ROM
; config before calling our user defined handlers. These stubs are only
; used if any other code uses the interrupt or break vectors. They are dead
; code otherwise, but since there is no other way to keep them in low memory,
; they have to go here.
IRQStub:
cld ; Just to be sure
lda MMU_CR ; Get old register value
pha ; And save on stack
lda #CC65_MMU_CFG ; Bank 0 with kernal ROM
sta MMU_CR
ldy #<(__IRQFUNC_COUNT__*2)
lda #<__IRQFUNC_TABLE__
ldx #>__IRQFUNC_TABLE__
jsr condes ; Call the functions
pla ; Get old register value
sta MMU_CR
jmp IRQInd ; Jump to the save IRQ vector
BRKStub:
pla ; Get original MMU_CR value
sta MMU_CR ; And set it
jmp BRKInd ; Jump indirect to break
; ------------------------------------------------------------------------
; Data
.data
zpsave: .res zpspace
; Old break vector preceeded by a jump opcode
BRKOld: jmp $0000
; Indirect vectors preceeded by a jump opcode
BRKInd: jmp $0000
.bss
spsave: .res 1
mmusave:.res 1