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https://github.com/cc65/cc65.git
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a3a22733f8
The BSS segment and the ONCE segment share the same start address. So they need to be placed in two different memory areas. So far BSS was placed in the MAIN memory area and ONCE was placed in an additional memory area. Both memory areas were written to the output file. They just "happened" to be loadable and runnable at a stretch. Now ONCE is placed in the MAIN memory area and BSS is placed in an additional memory area. Only MAIN is written to the output file. It becomes more obvious that BSS is "just" defined to share memory with ONCE.
119 lines
2.6 KiB
ArmAsm
119 lines
2.6 KiB
ArmAsm
;
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; Startup code for cc65 (C64 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 initlib, donelib
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.import zerobss, callmain
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.import BSOUT
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.import __MAIN_START__, __MAIN_SIZE__ ; Linker generated
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.import __STACKSIZE__ ; from configure file
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.importzp ST
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.include "zeropage.inc"
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.include "c64.inc"
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; ------------------------------------------------------------------------
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; Startup code
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.segment "STARTUP"
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Start:
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; Switch off the BASIC ROM.
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lda $01
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sta mmusave ; Save the memory configuration
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and #$F8
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ora #$06 ; Enable Kernal+I/O, disable BASIC
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sta $01
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tsx
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stx spsave ; Save the system stack ptr
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; Save space by putting some of the start-up code in the ONCE segment,
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; which can be re-used by the BSS segment, the heap and the C stack.
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jsr init
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; Clear the BSS data.
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jsr zerobss
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; Push the command-line arguments; and, call main().
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jsr callmain
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; Back from main() [this is also the exit() entry]. Run the module destructors.
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_exit: pha ; Save the return code on stack
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jsr donelib
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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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; Place the program return code into BASIC's status variable.
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pla
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sta ST
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; Restore the system stuff.
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ldx spsave
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txs ; Restore stack pointer
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ldx mmusave
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stx $01 ; Restore memory configuration
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; Back to BASIC.
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rts
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; ------------------------------------------------------------------------
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.segment "ONCE"
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init:
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; Save the zero-page locations that 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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; Set up the stack.
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lda #<(__MAIN_START__ + __MAIN_SIZE__)
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ldx #>(__MAIN_START__ + __MAIN_SIZE__)
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sta sp
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stx sp+1 ; Set argument stack ptr
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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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; Call the module constructors.
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jmp initlib
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; ------------------------------------------------------------------------
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; Data
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.segment "INIT"
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mmusave:.res 1
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spsave: .res 1
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zpsave: .res zpspace
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