;
; Startup code for cc65 (Plus/4 version)
-;
-; This must be the *first* file on the linker command line
;
- .export _exit
+ .export _exit
.export brk_jmp
+ .export __STARTUP__ : absolute = 1 ; Mark as startup
- .import condes, initlib, donelib
- .import push0, _main, zerobss
- .import __IRQFUNC_TABLE__, __IRQFUNC_COUNT__
+ .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"
; ------------------------------------------------------------------------
; Constants
-IRQInd = $500 ; JMP $0000 - used as indirect IRQ vector
+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.
+; Startup code
-.segment "STARTUP"
+.segment "STARTUP"
- .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
+Start:
-; ------------------------------------------------------------------------
-; Actual code
+; Save the zero-page locations that 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 ; save the zero page locations we need
- dex
- bpl L1
+ ldx #zpspace-1
+L1: lda sp,x
+ sta zpsave,x
+ dex
+ bpl L1
sta ENABLE_ROM
cli
-; Close open files
+; Switch to the second charset.
- jsr $FFCC ; CLRCH
+ lda #14
+ jsr $FFD2 ; BSOUT
-; Switch to second charset
+; Save some system stuff; and, set up the stack. The stack starts at the top
+; of the usable RAM.
- lda #14
- jsr $FFD2 ; BSOUT
+ tsx
+ stx spsave ; Save system stk ptr
+
+ lda #<(__MAIN_START__ + __MAIN_SIZE__ + __STACKSIZE__)
+ ldx #>(__MAIN_START__ + __MAIN_SIZE__ + __STACKSIZE__)
+ sta sp
+ stx sp+1
-; Setup the IRQ vector in the banked RAM and switch off the ROM
+; Set up 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
- lda #<IRQ
- sta $FFFE ; Install interrupt handler
- lda #>IRQ
- sta $FFFF
+ stx $FFFE ; Install interrupt handler
+ sty $FFFF
cli ; Allow interrupts
-; Clear the BSS data
+; Clear the BSS data.
- jsr zerobss
+ jsr zerobss
-; Save system stuff and setup the stack. The stack starts at the top of the
-; usable RAM.
-
- tsx
- stx spsave ; save system stk ptr
-
- lda #<$FD00
- sta sp
- lda #>$FD00
- sta sp+1
+; Initialize irqcount, which means that, from now on, custom linked-in IRQ
+; handlers will be called (via condes).
-; Call module constructors
+ lda #.lobyte(__INTERRUPTOR_COUNT__*2)
+ sta irqcount
- jsr initlib
+; Call the module constructors.
-; If we have IRQ functions, chain our stub into the IRQ vector
+ jsr initlib
- 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
+; Push the command-line arguments; and, call main().
-; Pass an empty command line
+ jsr callmain
-NoIRQ1: jsr push0 ; argc
- jsr push0 ; argv
+; Back from main() [this is also the exit() entry]. Run the module destructors.
- ldy #4 ; Argument size
- jsr _main ; call the users code
+_exit: pha ; Save the return code
+ jsr donelib ; Run module destructors
-; Back from main (this is also the _exit entry). Reset the IRQ vector if
-; we chained it.
+; Disable the chained IRQ handlers.
-_exit: lda #<__IRQFUNC_COUNT__
- beq NoIRQ2
- lda IRQInd+1
- ldx IRQInd+2
- sei
- sta IRQVec
- stx IRQVec+1
- cli
+ lda #0
+ sta irqcount ; Disable custom IRQ handlers
-; Run module destructors.
+; Copy back the zero-page stuff.
-NoIRQ2: jsr donelib ; Run module destructors
+ ldx #zpspace-1
+L2: lda zpsave,x
+ sta sp,x
+ dex
+ bpl L2
-; Restore system stuff
+; Place the program return code into BASIC's status variable.
- ldx spsave
- txs
+ 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
-; Enable the ROM, reset changed vectors and return to BASIC
+; Enable the ROM; and, return to BASIC.
sta ENABLE_ROM
- jmp $FF8A ; RESTOR
-
+ rts
; ------------------------------------------------------------------------
-; IRQ handler
+; 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: pha
+IRQ: cld ; Just to be sure
+ pha
txa
pha
+ tya
+ pha
tsx ; Get the stack pointer
- lda $0103,x ; Get the saved status register
- tax ; Save for later
+ lda $0104,x ; Get the saved status register
and #$10 ; Test for BRK bit
bne dobreak
- lda #>irq_ret ; Push new return address
+
+; It's an IRQ; and, RAM is enabled. If we have handlers, call them. We will use
+; a flag here instead of loading __INTERRUPTOR_COUNT__ directly, since the
+; condes function is not reentrant. The irqcount flag will be set/reset from
+; the main code, to avoid races.
+
+ ldy irqcount
+ beq @L1
+ jsr callirq_y ; Call the IRQ functions
+
+; Since the ROM handler will end with an RTI, we have to fake an IRQ return
+; on the stack, so that we get control of the CPU after the ROM handler,
+; and can switch back to RAM.
+
+@L1: lda #>irq_ret ; Push new return address
pha
lda #<irq_ret
pha
- txa
- pha
+ php ; Push faked IRQ frame on stack
+ pha ; Push faked A register
+ pha ; Push faked X register
+ pha ; Push faked Y register
sta ENABLE_ROM ; Switch to ROM
- jmp ($FFFE) ; Jump to kernal irq handler
+ jmp (IRQVec) ; Jump indirect to Kernal IRQ handler
irq_ret:
sta ENABLE_RAM ; Switch back to RAM
pla
+ tay
+ pla
tax
pla
rti
beq nohandler
jmp brk_jmp ; Jump to the handler
-; No break handler installed, jump to ROM
+; No break handler installed, jump to ROM.
nohandler:
- tya
- pha ; ROM handler expects Y on stack
sta ENABLE_ROM
jmp (BRKVec) ; Jump indirect to the break vector
-; ------------------------------------------------------------------------
-; Stub for the IRQ chain. Is used only if there are IRQs defined. Needed in
-; low memory because of the banking.
-
-.segment "LOWCODE"
-
-IRQStub:
- cld ; Just to be sure
- sta ENABLE_RAM ; Switch to RAM
- ldy #<(__IRQFUNC_COUNT__*2)
- lda #<__IRQFUNC_TABLE__
- ldx #>__IRQFUNC_TABLE__
- jsr condes ; Call the IRQ functions
- sta ENABLE_ROM
- jmp IRQInd ; Jump to the saved IRQ vector
-
; ------------------------------------------------------------------------
; Data
.data
-zpsave: .res zpspace
; BRK handling
brk_jmp: jmp $0000
-.bss
-spsave: .res 1
+spsave: .res 1
+
+irqcount: .byte 0
+
+.segment "INIT"
+zpsave: .res zpspace
projects / cc65 / blobdiff