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8216bf1d6a
main() is encountered. Define this symbol in the startup code. This will automatically force linking of the startup code which can then reside inside the standard library as any other object file. git-svn-id: svn://svn.cc65.org/cc65/trunk@3988 b7a2c559-68d2-44c3-8de9-860c34a00d81
193 lines
4.5 KiB
ArmAsm
193 lines
4.5 KiB
ArmAsm
;
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; Startup code for cc65 (C128 version)
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;
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.export _exit
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.export __STARTUP__ : absolute = 1 ; Mark as startup
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.import callirq, initlib, donelib
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.import zerobss
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.import push0, callmain
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.import RESTOR, BSOUT, CLRCH
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.import __INTERRUPTOR_COUNT__
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.import __RAM_START__, __RAM_SIZE__
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.include "zeropage.inc"
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.include "c128.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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; Place the startup code in a special segment to cope with the quirks of
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; c128 banking.
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.segment "STARTUP"
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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 .version ; 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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; Close open files
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jsr CLRCH
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; Switch to the second charset
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lda #14
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jsr BSOUT
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; Before doing anything else, we have to setup our banking configuration.
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; Otherwise just the lowest 16K are actually RAM. Writing through the ROM
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; to the underlying RAM works, but it is bad style.
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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 #MMU_CFG_CC65 ; Bank0 with kernal ROM
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sta MMU_CR
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; Save the zero page locations we need
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ldx #zpspace-1
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L1: lda sp,x
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sta zpsave,x
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dex
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bpl L1
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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 the system stack pointer
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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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; If we have IRQ functions, chain our stub into the IRQ vector
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lda #<__INTERRUPTOR_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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; Call module constructors
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NoIRQ1: jsr initlib
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; Set the bank for the file name to our execution bank. We must do this,
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; *after* calling constructors, because some of them may depend on the
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; original value of this register.
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lda #0
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sta FNAM_BANK
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; Push arguments and call main()
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jsr callmain
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; Back from main (this is also the _exit entry). Run module destructors
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_exit: jsr donelib
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; Reset the IRQ vector if we chained it.
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pha ; Save the return code on stack
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lda #<__INTERRUPTOR_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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; Copy back the zero page stuff
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NoIRQ2: 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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; Place the program return code into ST
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pla
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sta ST
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; Reset the stack and the memory configuration
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ldx spsave
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txs
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ldx mmusave
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stx MMU_CR
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; Done, restore kernal vectors in an attempt to cleanup
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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. To solve this, we place
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; the following code into a special segment called "LOWCODE" which will be
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; placed just above the startup code, so it goes into a RAM area that is
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; not banked.
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.segment "LOWCODE"
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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 #MMU_CFG_CC65 ; Bank 0 with kernal ROM
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sta MMU_CR
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jsr callirq ; 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 saved IRQ vector
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; ------------------------------------------------------------------------
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; Data
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.segment "ZPSAVE"
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zpsave: .res zpspace
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.bss
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spsave: .res 1
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mmusave:.res 1
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