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cc65/libsrc/plus4/crt0.s
cuz cfef8e1e0d Renamed __IRQFUNC_xxx -> __INTERRUPTOR_xxx
git-svn-id: svn://svn.cc65.org/cc65/trunk@3189 b7a2c559-68d2-44c3-8de9-860c34a00d81
2004-09-20 10:24:59 +00:00

207 lines
5.1 KiB
ArmAsm

;
; Startup code for cc65 (Plus/4 version)
;
; This must be the *first* file on the linker command line
;
.export _exit
.export brk_jmp
.import callirq_y, initlib, donelib
.import push0, callmain, zerobss
.import __INTERRUPTOR_COUNT__
.include "zeropage.inc"
.include "plus4.inc"
; ------------------------------------------------------------------------
; Constants
IRQInd = $500 ; JMP $0000 - used as indirect IRQ vector
; ------------------------------------------------------------------------
; Place the startup code in a special segment to cope with the quirks of
; plus/4 banking.
.segment "STARTUP"
.word Head ; Load address
Head: .word @Next
.word .version ; Line number
.byte $9E,"4109" ; SYS 4109
.byte $00 ; End of BASIC line
@Next: .word 0 ; BASIC end marker
; ------------------------------------------------------------------------
; Actual code
sei ; No interrupts since we're banking out the ROM
sta ENABLE_RAM
ldx #zpspace-1
L1: lda sp,x
sta zpsave,x ; save the zero page locations we need
dex
bpl L1
sta ENABLE_ROM
cli
; Close open files
jsr $FFCC ; CLRCH
; Switch to second charset
lda #14
jsr $FFD2 ; BSOUT
; Save system stuff and setup the stack. The stack starts at the top of the
; usable RAM.
tsx
stx spsave ; save system stk ptr
lda #<$FD00
sta sp
lda #>$FD00
sta sp+1
; Setup the IRQ vector in the banked RAM and switch off the ROM
ldx #<IRQ
ldy #>IRQ
sei ; No ints, handler not yet in place
sta ENABLE_RAM
stx $FFFE ; Install interrupt handler
sty $FFFF
cli ; Allow interrupts
; Clear the BSS data
jsr zerobss
; Call module constructors
jsr initlib
; Initialize irqcount, which means that from now own custom linked in IRQ
; handlers (via condes) will be called.
lda #.lobyte(__INTERRUPTOR_COUNT__*2)
sta irqcount
; Push arguments and call main()
jsr callmain
; Back from main (this is also the _exit entry). Run module destructors.
_exit: pha ; Save the return code
lda #0
sta irqcount ; Disable custom IRQ handlers
jsr donelib ; Run module destructors
; Copy back the zero page stuff
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
; Enable the ROM, reset changed vectors and return to BASIC
sta ENABLE_ROM
jmp $FF8A ; RESTOR
; ------------------------------------------------------------------------
; IRQ handler. The handler in the ROM enables the kernal and jumps to
; $CE00, where the ROM code checks for a BRK or IRQ and branches via the
; indirect vectors at $314/$316.
; To make our stub as fast as possible, we skip the whole part of the ROM
; handler and jump to the indirect vectors directly. We do also call our
; own interrupt handlers if we have any, so they need not use $314.
.segment "LOWCODE"
IRQ: cld ; Just to be sure
pha
txa
pha
tya
pha
tsx ; Get the stack pointer
lda $0104,x ; Get the saved status register
and #$10 ; Test for BRK bit
bne dobreak
; It's an IRQ and RAM is enabled. If we have handlers, call them. We will use
; a flag here instead of loading __INTERRUPTOR_COUNT__ directly, since the
; condes function is not reentrant. The irqcount flag will be set/reset from
; the main code, to avoid races.
ldy irqcount
beq @L1
jsr callirq_y ; Call the IRQ functions
; Since the ROM handler will end with an RTI, we have to fake an IRQ return
; on stack, so we get control of the CPU after the ROM handler and can switch
; back to RAM.
@L1: lda #>irq_ret ; Push new return address
pha
lda #<irq_ret
pha
php ; Push faked IRQ frame on stack
pha ; Push faked A register
pha ; Push faked X register
pha ; Push faked Y register
sta ENABLE_ROM ; Switch to ROM
jmp (IRQVec) ; Jump indirect to kernal irq handler
irq_ret:
sta ENABLE_RAM ; Switch back to RAM
pla
tay
pla
tax
pla
rti
dobreak:
lda brk_jmp+2 ; Check high byte of address
beq nohandler
jmp brk_jmp ; Jump to the handler
; No break handler installed, jump to ROM
nohandler:
sta ENABLE_ROM
jmp (BRKVec) ; Jump indirect to the break vector
; ------------------------------------------------------------------------
; Data
.data
zpsave: .res zpspace
; BRK handling
brk_jmp: jmp $0000
spsave: .res 1
.bss
irqcount: .byte 0