mirror of
https://github.com/cc65/cc65.git
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7e65f64c6a
and NMI to make sure the NMI handler is loaded into the low 16K of memory which are active when the control is passed from the ROM NMI stub to the user handler. git-svn-id: svn://svn.cc65.org/cc65/trunk@1086 b7a2c559-68d2-44c3-8de9-860c34a00d81
233 lines
5.4 KiB
ArmAsm
233 lines
5.4 KiB
ArmAsm
;
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; Startup code for cc65 (C128 version)
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;
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; This must be the *first* file on the linker command line
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;
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.export _exit
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.export BRKStub, BRKOld, BRKInd
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.import condes, initlib, donelib
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.import initconio, doneconio, zerobss
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.import push0, _main
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.import __IRQFUNC_TABLE__, __IRQFUNC_COUNT__
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.import __RAM_START__, __RAM_SIZE__
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.include "c128.inc"
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.include "../cbm/cbm.inc"
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; ------------------------------------------------------------------------
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; Constants
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IRQInd = $2FD ; JMP $0000 - used as indirect IRQ vector
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; ------------------------------------------------------------------------
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; Define and export the ZP variables for the C64 runtime
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.exportzp sp, sreg, regsave
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.exportzp ptr1, ptr2, ptr3, ptr4
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.exportzp tmp1, tmp2, tmp3, tmp4
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.exportzp regbank, zpspace
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.zeropage
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zpstart = *
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sp: .res 2 ; Stack pointer
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sreg: .res 2 ; Secondary register/high 16 bit for longs
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regsave: .res 2 ; slot to save/restore (E)AX into
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ptr1: .res 2
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ptr2: .res 2
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ptr3: .res 2
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ptr4: .res 2
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tmp1: .res 1
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tmp2: .res 1
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tmp3: .res 1
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tmp4: .res 1
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regbank: .res 6 ; 6 byte register bank
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zpspace = * - zpstart ; Zero page space allocated
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; Place the startup code in a special segment to cope with the quirks of
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; c128 banking. Do also create an empty segment named "NMI" to avoid
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; warnings if the rs232 routines are not used.
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.segment "NMI"
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; empty
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.segment "STARTUP"
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; ------------------------------------------------------------------------
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; BASIC header with a SYS call
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.org $1BFF
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.word Head ; Load address
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Head: .word @Next
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.word 1000 ; Line number
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.byte $9E,"7181" ; SYS 7181
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.byte $00 ; End of BASIC line
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@Next: .word 0 ; BASIC end marker
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.reloc
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; ------------------------------------------------------------------------
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; Actual code
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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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bpl L1
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; Close open files
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jsr CLRCH
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; Switch to second charset
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lda #14
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jsr BSOUT
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; Get the current MMU setting and save it. Set new memory config.
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lda MMU_CR ; Get current memory configuration...
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pha ; ...and save it for later
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lda #CC65_MMU_CFG ; Bank0 with kernal ROM
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sta MMU_CR
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; Clear the BSS data
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jsr zerobss
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; Save system stuff and setup the stack
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pla ; Get MMU setting
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sta mmusave
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tsx
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stx spsave ; save system stk ptr
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lda #<(__RAM_START__ + __RAM_SIZE__)
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sta sp
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lda #>(__RAM_START__ + __RAM_SIZE__)
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sta sp+1 ; Set argument stack ptr
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; Call module constructors
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jsr initlib
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; Initialize conio stuff
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jsr initconio
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; If we have IRQ functions, chain our stub into the IRQ vector
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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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; Pass an empty command line
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NoIRQ1: jsr push0 ; argc
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jsr push0 ; argv
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ldy #4 ; Argument size
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jsr _main ; call the users code
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; This is also the _exit entry. Reset the IRQ vector if we chained it.
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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
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; Reset the conio stuff
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jsr doneconio
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; Reset stack and the MMU
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ldx spsave
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txs
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lda mmusave
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sta MMU_CR
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; Copy back the zero page stuff
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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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bpl L2
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; Done
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jmp RESTOR
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; ------------------------------------------------------------------------
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; The C128 has ROM parallel to the RAM starting from $4000. The startup code
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; above will change this setting so that we have RAM from $0000-$BFFF. This
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; works quite well with the exception of interrupts: The interrupt handler
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; is in ROM, and the ROM switches back to the ROM configuration, which means
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; that parts of our program may not be accessible. Since the crt0 module is
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; the first module in the program, it will always be below $4000 and always
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; in RAM. So we place several short stubs here that switch back our ROM
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; config before calling our user defined handlers. These stubs are only
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; used if any other code uses the interrupt or break vectors. They are dead
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; code otherwise, but since there is no other way to keep them in low memory,
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; they have to go here.
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IRQStub:
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cld ; Just to be sure
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lda MMU_CR ; Get old register value
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pha ; And save on stack
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lda #CC65_MMU_CFG ; Bank 0 with kernal ROM
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sta MMU_CR
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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 functions
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pla ; Get old register value
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sta MMU_CR
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jmp IRQInd ; Jump to the save IRQ vector
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BRKStub:
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pla ; Get original MMU_CR value
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sta MMU_CR ; And set it
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jmp BRKInd ; Jump indirect to break
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; ------------------------------------------------------------------------
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; Data
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.data
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zpsave: .res zpspace
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; Old break vector preceeded by a jump opcode
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BRKOld: jmp $0000
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; Indirect vectors preceeded by a jump opcode
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BRKInd: jmp $0000
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.bss
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spsave: .res 1
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mmusave:.res 1
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