;
; Startup code for cc65 (Plus/4 version)
-;
-; This must be the *first* file on the linker command line
;
.export _exit
- .import __hinit, push0, doatexit, _main
- .import initconio, doneconio, zerobss
+ .export brk_jmp
+ .export __STARTUP__ : absolute = 1 ; Mark as startup
+
+ .import callirq_y, initlib, donelib
+ .import callmain, zerobss
+ .import __INTERRUPTOR_COUNT__
+ .include "zeropage.inc"
.include "plus4.inc"
- .include "../cbm/cbm.inc"
+
; ------------------------------------------------------------------------
-; 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
-
-sp = $02 ; stack pointer
-sreg = $04 ; secondary register/high 16 bit for longs
-regsave = $06 ; slot to save/restore (E)AX into
-ptr1 = $0A ;
-ptr2 = $0C
-ptr3 = $0E
-ptr4 = $10
-tmp1 = $12
-tmp2 = $13
-tmp3 = $14
-tmp4 = $15
-regbank = $16 ; 6 byte register bank
-zpspace = $1A ; Zero page space allocated
+; Constants
+
+IRQInd = $500 ; JMP $0000 - used as indirect IRQ vector
; ------------------------------------------------------------------------
; BASIC header with a SYS call
- .org $0FFF
+.segment "EXEHDR"
+
.word Head ; Load address
Head: .word @Next
- .word 1000 ; Line number
- .byte $9E,"4109" ; SYS 4109
+ .word .version ; Line number
+ .byte $9E ; SYS token
+ .byte <(((Start / 1000) .mod 10) + '0')
+ .byte <(((Start / 100) .mod 10) + '0')
+ .byte <(((Start / 10) .mod 10) + '0')
+ .byte <(((Start / 1) .mod 10) + '0')
.byte $00 ; End of BASIC line
@Next: .word 0 ; BASIC end marker
- .reloc
; ------------------------------------------------------------------------
-; Actual code
+; Startup code
- ldy #zpspace-1
-L1: lda sp,y
- sta zpsave,y ; save the zero page locations we need
- dey
- bpl L1
+.segment "STARTUP"
-; Close open files
+Start:
- jsr CLRCH
+; Save the zero page locations we need
+
+ sei ; No interrupts since we're banking out the ROM
+ sta ENABLE_RAM
+ ldx #zpspace-1
+L1: lda sp,x
+ sta zpsave,x
+ dex
+ bpl L1
+ sta ENABLE_ROM
+ cli
; Switch to second charset
- lda #14
- jsr BSOUT
+ lda #14
+ jsr $FFD2 ; BSOUT
-; Clear the BSS data
+; Save system stuff and setup the stack. The stack starts at the top of the
+; usable RAM.
+
+ tsx
+ stx spsave ; save system stk ptr
- jsr zerobss
+ lda #<$FD00
+ sta sp
+ lda #>$FD00
+ sta sp+1
-; Save system stuff and setup the stack
+; Setup the IRQ vector in the banked RAM and switch off the ROM
- tsx
- stx spsave ; save system stk ptr
+ 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
- sec
- jsr MEMTOP ; Get top memory
- cpy #$80 ; We can only use the low 32K :-(
- bcc MemOk
- ldy #$80
- ldx #$00
-MemOk: stx sp
- sty sp+1 ; set argument stack ptr
+; Clear the BSS data
-; Initialize the heap
+ jsr zerobss
- jsr __hinit
+; Initialize irqcount, which means that from now own custom linked in IRQ
+; handlers (via condes) will be called.
-; Initialize conio stuff
+ lda #.lobyte(__INTERRUPTOR_COUNT__*2)
+ sta irqcount
- jsr initconio
+; Call module constructors
-; Pass an empty command line
+ jsr initlib
- jsr push0 ; argc
- jsr push0 ; argv
+; Push arguments and call main()
- ldy #4 ; Argument size
- jsr _main ; call the users code
+ jsr callmain
-; fall thru to exit...
+; Back from main (this is also the _exit entry). Run module destructors.
-_exit: jsr doatexit ; call exit functions
- ldx spsave
- txs
+_exit: pha ; Save the return code
+ jsr donelib ; Run module destructors
-; Reset the conio stuff
+; Disable chained IRQ handlers
- jsr doneconio
+ lda #0
+ sta irqcount ; Disable custom IRQ handlers
; Copy back the zero page stuff
- ldy #zpspace-1
-L2: lda zpsave,y
- sta sp,y
- dey
+ ldx #zpspace-1
+L2: lda zpsave,x
+ sta sp,x
+ dex
bpl L2
-; Reset changed vectors
+; Place the program return code into ST
- jmp RESTOR
+ 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
-.bss
-spsave: .res 1
+; BRK handling
+brk_jmp: jmp $0000
+
+spsave: .res 1
+
+irqcount: .byte 0
+
+.segment "ZPSAVE"
+
+zpsave: .res zpspace
projects / cc65 / blobdiff