Added a serial driver for the builtin 6551 of the Plus/4 (untested, but taken
mostly from the C64 version which is tested and works). Improved interrupt handling (was needed for the driver). git-svn-id: svn://svn.cc65.org/cc65/trunk@2754 b7a2c559-68d2-44c3-8de9-860c34a00d81
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cuz
@@ -41,33 +41,19 @@ Head: .word @Next
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ldx #zpspace-1
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L1: lda sp,x
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sta zpsave,x ; save the zero page locations we need
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dex
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dex
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bpl L1
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sta ENABLE_ROM
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cli
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; Close open files
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jsr $FFCC ; CLRCH
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jsr $FFCC ; CLRCH
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; Switch to second charset
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lda #14
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jsr $FFD2 ; BSOUT
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; Setup the IRQ vector in the banked RAM and switch off the ROM
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sei ; No ints, handler not yet in place
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sta ENABLE_RAM
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lda #<IRQ
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sta $FFFE ; Install interrupt handler
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lda #>IRQ
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sta $FFFF
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cli ; Allow interrupts
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; Clear the BSS data
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jsr zerobss
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lda #14
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jsr $FFD2 ; BSOUT
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; Save system stuff and setup the stack. The stack starts at the top of the
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; usable RAM.
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@@ -80,88 +66,110 @@ L1: lda sp,x
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lda #>$FD00
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sta sp+1
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; Setup the IRQ vector in the banked RAM and switch off the ROM
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ldx #<IRQ
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ldy #>IRQ
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sei ; No ints, handler not yet in place
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sta ENABLE_RAM
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stx $FFFE ; Install interrupt handler
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sty $FFFF
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cli ; Allow interrupts
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; Clear the BSS data
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jsr zerobss
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; Call module constructors
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jsr initlib
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jsr initlib
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; If we have IRQ functions, chain our stub into the IRQ vector
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; Initialize irqcount, which means that from now own custom linked in IRQ
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; handlers (via condes) will be called.
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lda #<__IRQFUNC_COUNT__
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beq NoIRQ1
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lda IRQVec
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ldx IRQVec+1
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sta IRQInd+1
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stx IRQInd+2
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lda #<IRQStub
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ldx #>IRQStub
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sei
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sta IRQVec
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stx IRQVec+1
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cli
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lda #.lobyte(__IRQFUNC_COUNT__*2)
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sta irqcount
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; Push arguments and call main()
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NoIRQ1: jsr callmain
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jsr callmain
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; Back from main (this is also the _exit entry). Reset the IRQ vector if
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; we chained it.
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; Back from main (this is also the _exit entry). Run module destructors.
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_exit: lda #<__IRQFUNC_COUNT__
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beq NoIRQ2
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lda IRQInd+1
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ldx IRQInd+2
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sei
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sta IRQVec
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stx IRQVec+1
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cli
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; Run module destructors.
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NoIRQ2: jsr donelib ; Run module destructors
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_exit: lda #0
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sta irqcount ; Disable custom IRQ handlers
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jsr donelib ; Run module destructors
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; Restore system stuff
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ldx spsave
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txs
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ldx spsave
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txs
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; Copy back the zero page stuff
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ldx #zpspace-1
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ldx #zpspace-1
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L2: lda zpsave,x
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sta sp,x
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dex
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sta sp,x
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dex
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bpl L2
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; Enable the ROM, reset changed vectors and return to BASIC
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sta ENABLE_ROM
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jmp $FF8A ; RESTOR
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jmp $FF8A ; RESTOR
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; ------------------------------------------------------------------------
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; IRQ handler
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; IRQ handler. The handler in the ROM enables the kernal and jumps to
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; $CE00, where the ROM code checks for a BRK or IRQ and branches via the
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; indirect vectors at $314/$316.
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; To make our stub as fast as possible, we skip the whole part of the ROM
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; handler and jump to the indirect vectors directly. We do also call our
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; own interrupt handlers if we have any, so they need not use $314.
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.segment "LOWCODE"
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IRQ: pha
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IRQ: cld ; Just to be sure
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pha
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txa
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pha
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tya
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pha
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tsx ; Get the stack pointer
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lda $0103,x ; Get the saved status register
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tax ; Save for later
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lda $0104,x ; Get the saved status register
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and #$10 ; Test for BRK bit
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bne dobreak
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lda #>irq_ret ; Push new return address
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; It's an IRQ and RAM is enabled. If we have handlers, call them. We will use
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; a flag here instead of loading __IRQFUNC_COUNT__ directly, since the condes
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; function is not reentrant. The irqcount flag will be set/reset from the main
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; code, to avoid races.
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ldy irqcount
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beq @L1
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lda #<__IRQFUNC_TABLE__
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ldx #>__IRQFUNC_TABLE__
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jsr condes ; Call the IRQ functions
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; Since the ROM handler will end with an RTI, we have to fake an IRQ return
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; on stack, so we get control of the CPU after the ROM handler and can switch
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; back to RAM.
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@L1: lda #>irq_ret ; Push new return address
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pha
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lda #<irq_ret
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pha
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txa
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pha
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php ; Push faked IRQ frame on stack
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pha ; Push faked A register
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pha ; Push faked X register
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pha ; Push faked Y register
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sta ENABLE_ROM ; Switch to ROM
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jmp ($FFFE) ; Jump to kernal irq handler
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jmp (IRQVec) ; Jump indirect to kernal irq handler
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irq_ret:
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sta ENABLE_RAM ; Switch back to RAM
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pla
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tay
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pla
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tax
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pla
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@@ -175,27 +183,9 @@ dobreak:
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; No break handler installed, jump to ROM
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nohandler:
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tya
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pha ; ROM handler expects Y on stack
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sta ENABLE_ROM
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jmp (BRKVec) ; Jump indirect to the break vector
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; ------------------------------------------------------------------------
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; Stub for the IRQ chain. Is used only if there are IRQs defined. Needed in
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; low memory because of the banking.
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.segment "LOWCODE"
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IRQStub:
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cld ; Just to be sure
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sta ENABLE_RAM ; Switch to RAM
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ldy #<(__IRQFUNC_COUNT__*2)
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lda #<__IRQFUNC_TABLE__
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ldx #>__IRQFUNC_TABLE__
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jsr condes ; Call the IRQ functions
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sta ENABLE_ROM
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jmp IRQInd ; Jump to the saved IRQ vector
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; ------------------------------------------------------------------------
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; Data
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@@ -205,8 +195,8 @@ zpsave: .res zpspace
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; BRK handling
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brk_jmp: jmp $0000
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.bss
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spsave: .res 1
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.bss
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irqcount: .byte 0
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