;
; 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 _exit
+ .export brk_jmp
+ .export __STARTUP__ : absolute = 1 ; Mark as startup
+
+ .import callirq_y, initlib, donelib
+ .import callmain, zerobss
+ .import __INTERRUPTOR_COUNT__
+ .import __MAIN_START__, __MAIN_SIZE__ ; Linker generated
+ .import __STACKSIZE__ ; Linker generated
+ .importzp ST
+
+ .include "zeropage.inc"
+ .include "plus4.inc"
- .include "plus4.inc"
- .include "../cbm/cbm.inc"
; ------------------------------------------------------------------------
-; Define and export the ZP variables for the C64 runtime
+; Constants
- .exportzp sp, sreg, regsave
- .exportzp ptr1, ptr2, ptr3, ptr4
- .exportzp tmp1, tmp2, tmp3, tmp4
- .exportzp regbank, zpspace
+IRQInd = $500 ; JMP $0000 - used as indirect IRQ vector
-.zeropage
+; ------------------------------------------------------------------------
+; Startup code
-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
+.segment "STARTUP"
-zpspace = * - zpstart ; Zero page space allocated
+Start:
-.code
+; Save the zero-page locations that we need.
-; ------------------------------------------------------------------------
-; BASIC header with a SYS call
+ 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
- .org $0FFF
- .word Head ; Load address
-Head: .word @Next
- .word 1000 ; Line number
- .byte $9E,"4109" ; SYS 4109
- .byte $00 ; End of BASIC line
-@Next: .word 0 ; BASIC end marker
- .reloc
+; Switch to the second charset.
-; ------------------------------------------------------------------------
-; Actual code
+ lda #14
+ jsr $FFD2 ; BSOUT
- ldx #zpspace-1
-L1: lda sp,x
- sta zpsave,x ; save the zero page locations we need
- dex
- bpl L1
+; Save some system stuff; and, set up the stack. The stack starts at the top
+; of the usable RAM.
-; Close open files
+ tsx
+ stx spsave ; Save system stk ptr
- jsr CLRCH
+ lda #<(__MAIN_START__ + __MAIN_SIZE__ + __STACKSIZE__)
+ ldx #>(__MAIN_START__ + __MAIN_SIZE__ + __STACKSIZE__)
+ sta sp
+ stx sp+1
-; Switch to second charset
+; Set up the IRQ vector in the banked RAM; and, switch off the ROM.
- lda #14
- jsr BSOUT
+ 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
+; Clear the BSS data.
- jsr zerobss
+ jsr zerobss
-; Save system stuff and setup the stack
+; Initialize irqcount, which means that, from now on, custom linked-in IRQ
+; handlers will be called (via condes).
- tsx
- stx spsave ; save system stk ptr
+ lda #.lobyte(__INTERRUPTOR_COUNT__*2)
+ sta irqcount
- 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
+; Call the module constructors.
-; Initialize the heap
+ jsr initlib
- jsr __hinit
+; Push the command-line arguments; and, call main().
-; Initialize conio stuff
+ jsr callmain
- jsr initconio
+; Back from main() [this is also the exit() entry]. Run the module destructors.
-; Pass an empty command line
+_exit: pha ; Save the return code
+ jsr donelib ; Run module destructors
- jsr push0 ; argc
- jsr push0 ; argv
+; Disable the chained IRQ handlers.
- ldy #4 ; Argument size
- jsr _main ; call the users code
+ lda #0
+ sta irqcount ; Disable custom IRQ handlers
-; fall thru to exit...
+; Copy back the zero-page stuff.
-_exit: jsr doatexit ; call exit functions
- ldx spsave
- txs
+ ldx #zpspace-1
+L2: lda zpsave,x
+ sta sp,x
+ dex
+ bpl L2
-; Reset the conio stuff
+; Place the program return code into BASIC's status variable.
- jsr doneconio
+ pla
+ sta ST
-; Copy back the zero page stuff
+; Restore the stack pointer.
- ldx #zpspace-1
-L2: lda zpsave,x
- sta sp,x
- dex
- bpl L2
+ ldx spsave
+ txs
-; Reset changed vectors
+; Enable the ROM; and, return to BASIC.
- jmp RESTOR
+ sta ENABLE_ROM
+ rts
+; ------------------------------------------------------------------------
+; 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 the stack, so that 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 "INIT"
+
+zpsave: .res zpspace
projects / cc65 / blobdiff