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https://github.com/cc65/cc65.git
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489 lines
11 KiB
ArmAsm
489 lines
11 KiB
ArmAsm
;
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; Startup code for cc65 (CBM 500 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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.import _clrscr, initlib, donelib
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.import push0, _main
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.import __CHARRAM_START__, __CHARRAM_SIZE__, __VIDRAM_START__
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.import __BSS_RUN__, __BSS_SIZE__
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.import irq, nmi
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.import k_irq, k_nmi, k_plot, k_udtim, k_scnkey
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.include "zeropage.inc"
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.include "cbm510.inc"
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; ------------------------------------------------------------------------
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; BASIC header and a small BASIC program. Since it is not possible to start
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; programs in other banks using SYS, the BASIC program will write a small
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; machine code program into memory at $100 and start that machine code
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; program. The machine code program will then start the machine language
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; code in bank 0, which will initialize the system by copying stuff from
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; the system bank, and start the application.
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;
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; Here's the basic program that's in the following lines:
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;
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; 10 for i=0 to 4
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; 20 read j
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; 30 poke 256+i,j
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; 40 next i
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; 50 sys 256
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; 60 data 120,169,0,133,0
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;
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; The machine program in the data lines is:
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;
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; sei
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; lda #$00
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; sta $00 <-- Switch to bank 0 after this command
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;
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; Initialization is not only complex because of the jumping from one bank
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; into another. but also because we want to save memory, and because of
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; this, we will use the system memory ($00-$3FF) for initialization stuff
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; that is overwritten later.
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;
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.code
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; To make things more simple, make the code of this module absolute.
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.org $0001
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Head: .byte $03,$00,$11,$00,$0a,$00,$81,$20,$49,$b2,$30,$20,$a4,$20,$34,$00
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.byte $19,$00,$14,$00,$87,$20,$4a,$00,$27,$00,$1e,$00,$97,$20,$32,$35
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.byte $36,$aa,$49,$2c,$4a,$00,$2f,$00,$28,$00,$82,$20,$49,$00,$39,$00
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.byte $32,$00,$9e,$20,$32,$35,$36,$00,$4f,$00,$3c,$00,$83,$20,$31,$32
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.byte $30,$2c,$31,$36,$39,$2c,$30,$2c,$31,$33,$33,$2c,$30,$00,$00,$00
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; Since we need some vectors to access stuff in the system bank for our own,
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; we will include them here, starting from $60:
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.res $60-*
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vic: .word $d800
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sid: .word $da00
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cia1: .word $db00
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cia2: .word $dc00
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acia: .word $dd00
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tpi1: .word $de00
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tpi2: .word $df00
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ktab1: .word $eab1
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ktab2: .word $eb11
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ktab3: .word $eb71
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ktab4: .word $ebd1
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time: .dword $0000
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RecvBuf: .word $0100 ; RS232 received buffer
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SendBuf: .word $0200 ; RS232 send buffer
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; The code in the target bank when switching back will be put at the bottom
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; of the stack. We will jump here to switch segments. The range $F2..$FF is
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; not used by any kernal routine.
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.res $F8-*
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Back: ldx spsave
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txs
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lda IndReg
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sta ExecReg
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; The following code is a copy of the code that is poked in the system bank
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; memory by the basic header program, it's only for documentation and not
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; actually used here:
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sei
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lda #$00
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sta ExecReg
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; This is the actual starting point of our code after switching banks for
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; startup. Beware: The following code will get overwritten as soon as we
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; use the stack (since it's in page 1)!
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tsx
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stx spsave ; Save the system stackpointer
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ldx #$FF
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txs ; Set up our own stack
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; Set the interrupt, NMI and other vectors
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ldy #vectable_size
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L0: lda vectable-1,y
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sta $FF80,y
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dey
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bne L0
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; Switch the indirect segment to the system bank
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lda #$0F
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sta IndReg
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; Copy the kernal zero page ($90-$F2) from the system bank
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lda #$90
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sta ptr1
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lda #$00
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sta ptr1+1
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ldy #$62-1
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L1: lda (ptr1),y
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sta $90,y
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dey
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bpl L1
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; Copy the page 3 vectors in place
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ldy #$00
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L2: lda p3vectable,y
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sta $300,y
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iny
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cpy #p3vectable_size
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bne L2
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; Copy the rest of page 3 from the system bank
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lda #$00
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sta ptr1
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lda #$03
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sta ptr1+1
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L3: lda (ptr1),y
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sta $300,y
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iny
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bne L3
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; Set the indirect segment to bank we're executing in
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lda ExecReg
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sta IndReg
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; Zero the BSS segment. We will do that here instead calling the routine
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; in the common library, since we have the memory anyway, and this way,
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; it's reused later.
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lda #<__BSS_RUN__
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sta ptr1
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lda #>__BSS_RUN__
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sta ptr1+1
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lda #0
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tay
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; Clear full pages
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ldx #>__BSS_SIZE__
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beq Z2
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Z1: sta (ptr1),y
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iny
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bne Z1
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inc ptr1+1 ; Next page
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dex
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bne Z1
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; Clear the remaining page
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Z2: ldx #<__BSS_SIZE__
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beq Z4
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Z3: sta (ptr1),y
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iny
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dex
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bne Z3
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Z4:
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; Setup the C stack
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lda #<$FF81
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sta sp
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lda #>$FF81
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sta sp+1
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; We expect to be in page 2 now
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.if (* < $1FD)
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jmp $200
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.res $200-*
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.endif
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.if (* < $200)
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.res $200-*,$EA
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.endif
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.if (* >= $2F0)
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.error "Code range invalid"
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.endif
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; This code is in page 2, so we may now start calling subroutines safely,
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; since the code we execute is no longer in the stack page.
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; Copy the character rom from the system bank into the execution bank
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lda #<$C000
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sta ptr1
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lda #>$C000
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sta ptr1+1
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lda #<__CHARRAM_START__
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sta ptr2
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lda #>__CHARRAM_START__
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sta ptr2+1
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lda #>__CHARRAM_SIZE__ ; 16 * 256 bytes to copy
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sta tmp1
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ldy #$00
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ccopy: lda #$0F
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sta IndReg ; Access the system bank
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ccopy1: lda (ptr1),y
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sta __VIDRAM_START__,y
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iny
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bne ccopy1
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lda ExecReg
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sta IndReg
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ccopy2: lda __VIDRAM_START__,y
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sta (ptr2),y
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iny
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bne ccopy2
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inc ptr1+1
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inc ptr2+1 ; Bump high pointer bytes
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dec tmp1
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bne ccopy
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; Clear the video memory. We will do this before switching the video to bank 0
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; to avoid garbage when doing so.
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jsr _clrscr
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; Reprogram the VIC so that the text screen and the character ROM is in the
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; execution bank. This is done in three steps:
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lda #$0F ; We need access to the system bank
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sta IndReg
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; Place the VIC video RAM into bank 0
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; CA (STATVID) = 0
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; CB (VICDOTSEL) = 0
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ldy #tpiCtrlReg
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lda (tpi1),y
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sta vidsave+0
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and #%00001111
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ora #%10100000
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sta (tpi1),y
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; Set bit 14/15 of the VIC address range to the high bits of __VIDRAM_START__
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; PC6/PC7 (VICBANKSEL 0/1) = 11
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ldy #tpiPortC
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lda (tpi2),y
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sta vidsave+1
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and #$3F
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ora #<((>__VIDRAM_START__) & $C0)
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sta (tpi2),y
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; Set the VIC base address register to the addresses of the video and
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; character RAM.
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ldy #VIC_VIDEO_ADR
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lda (vic),y
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sta vidsave+2
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and #$01
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ora #<(((__VIDRAM_START__ >> 6) & $F0) | ((__CHARRAM_START__ >> 10) & $0E) | $02)
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; and #$0F
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; ora #<(((>__VIDRAM_START__) << 2) & $F0)
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sta (vic),y
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; Switch back to the execution bank
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lda ExecReg
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sta IndReg
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; Call module constructors
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jsr initlib
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; Create the (empty) command line for the program
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jsr push0 ; argc
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jsr push0 ; argv
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; Execute the program code
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jmp Start
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; ------------------------------------------------------------------------
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; Additional data that we need for initialization and that's overwritten
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; later
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vectable:
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jmp $0000 ; CINT
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jmp $0000 ; IOINIT
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jmp $0000 ; RAMTAS
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jmp $0000 ; RESTOR
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jmp $0000 ; VECTOR
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jmp $0000 ; SETMSG
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jmp $0000 ; SECOND
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jmp $0000 ; TKSA
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jmp $0000 ; MEMTOP
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jmp $0000 ; MEMBOT
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jmp k_scnkey ; SCNKEY
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jmp $0000 ; SETTMO
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jmp $0000 ; ACPTR
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jmp $0000 ; CIOUT
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jmp $0000 ; UNTLK
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jmp $0000 ; UNLSN
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jmp $0000 ; LISTEN
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jmp $0000 ; TALK
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jmp $0000 ; READST
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jmp k_setlfs ; SETLFS
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jmp k_setnam ; SETNAM
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jmp $0000 ; OPEN
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jmp $0000 ; CLOSE
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jmp $0000 ; CHKIN
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jmp $0000 ; CKOUT
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jmp $0000 ; CLRCH
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jmp $0000 ; BASIN
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jmp $0000 ; BSOUT
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jmp $0000 ; LOAD
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jmp $0000 ; SAVE
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jmp k_settim ; SETTIM
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jmp k_rdtim ; RDTIM
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jmp $0000 ; STOP
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jmp $0000 ; GETIN
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jmp $0000 ; CLALL
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jmp k_udtim ; UDTIM
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jmp k_screen ; SCREEN
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jmp k_plot ; PLOT
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jmp k_iobase ; IOBASE
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sta ExecReg
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rts
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.byte $01 ; Filler
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.word nmi
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.word 0 ; Reset - not used
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.word irq
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vectable_size = * - vectable
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p3vectable:
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.word k_irq ; IRQ user vector
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.word k_brk ; BRK user vector
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.word k_nmi ; NMI user vector
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p3vectable_size = * - p3vectable
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; ------------------------------------------------------------------------
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; This is the program code after setup. It starts at $400
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.res $400-*
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Start:
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; Enable interrupts
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cli
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; Call the user code
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ldy #4 ; Argument size
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jsr _main ; call the users code
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; Call module destructors. This is also the _exit entry.
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_exit: jsr donelib ; Run module destructors
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; We need access to the system bank now
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lda #$0F
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sta IndReg
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; Switch back the video to the system bank
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ldy #tpiCtrlReg
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lda vidsave+0
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sta (tpi1),y
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ldy #tpiPortC
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lda vidsave+1
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sta (tpi2),y
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ldy #VIC_VIDEO_ADR
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lda vidsave+2
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sta (vic),y
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; Clear the start of the zero page, since it will be interpreted as a
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; (garbage) BASIC program otherwise. This is also the default entry for
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; the break vector.
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k_brk: sei
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lda #$00
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ldx #$3E
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Clear: sta $02,x
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dex
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bne Clear
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; Setup the welcome code at the stack bottom in the system bank. Use
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; the F4/F5 vector to access the system bank
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ldy #$00
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sty $F4
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iny
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sty $F5
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ldy #reset_size-1
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@L1: lda reset,y
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sta ($F4),y
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dey
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bne @L1
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jmp Back
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; ------------------------------------------------------------------------
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; Code that is copied into the system bank at $100 when switching back
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reset: cli
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jmp $8000 ; BASIC cold start
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reset_size = * - reset
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; ------------------------------------------------------------------------
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; Code for a few simpler kernal calls goes here
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k_iobase:
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ldx cia2
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ldy cia2+1
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rts
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k_screen:
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ldx #40 ; Columns
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ldy #25 ; Lines
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rts
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k_setlfs:
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sta LogicalAdr
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stx FirstAdr
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sty SecondAdr
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rts
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k_setnam:
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sta FileNameLen
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lda $00,x
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sta FileNameAdrLo
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lda $01,x
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sta FileNameAdrHi
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lda $02,x
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sta FileNameAdrSeg
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rts
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k_rdtim:
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sei
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lda time+0
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ldx time+1
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ldy time+2
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cli
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rts
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k_settim:
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sei
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sta time+0
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stx time+1
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sty time+2
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cli
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rts
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; -------------------------------------------------------------------------
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; Data area - switch back to relocatable mode
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.reloc
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.data
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spsave: .res 1
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vidsave:.res 3
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