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@ -0,0 +1,254 @@ |
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; ------------------------------------------------------------------------------ |
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; msx-ldr.asm |
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; MSX RomWBW loader, requires 512KB or more RAM mapper |
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; ------------------------------------------------------------------------------ |
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; The loader assumes following entry conditions: |
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; + RAM mapper slot is selected on all 4 pages |
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; + Segments 0 to 3 are in use for the DOS TPA |
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; + The last 2 segments may be in use for MSX-DOS 2 code + data |
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ROMWBW_SEG .equ 4 ; RomWBW boot segment |
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CHGCPU .equ $0180 ; changes CPU mode |
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P2_SEG .equ $f2c9 ; current segment page 2 (MSX-DOS 2) |
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CSRSW .equ $fca9 ; cursor on/off flag |
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H_TIMI .equ $fd9f ; timer interrupt hook (vdp vsync) |
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; ------------------------------------------------------------------------------ |
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.ORG $100 |
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; copy loader to page 3 and run it there |
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ld hl,LSTART |
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ld de,$c000 |
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ld bc,LSIZE |
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ldir |
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jp $c000 |
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LSTART: |
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; ------------------------------------------------------------------------------ |
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.ORG $c000 |
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; open ROM image file (fcb) |
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ld de,romfile |
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ld c,$0f ; FOPEN |
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call 5 |
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or a ; error opening file? |
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jp nz,error_open ; nz=yes |
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; get filesize, determine number of ram segments to load |
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ld a,(romfile+$12) ; rom image size / 64k bytes |
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rlca ; number of banks |
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rlca ; number of segments |
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ld (nsegs),a |
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; determine ram mapper size |
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call MapperSize |
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or a |
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jp z,error_noram |
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; mapper segments > nsegs + 5? |
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ld a,(nsegs) |
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add a,5 |
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sub b |
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jp nc,error_ramsize |
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ld de,t_message |
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ld c,$09 ; STROUT |
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call 5 |
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; init fcb file read: set recordsize and disk transfer address |
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ld hl,$0400 ; use 1K blocks |
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ld (romfile+$0e),hl |
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ld de,$8000 |
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ld c,$1a ; SETDTA |
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call 5 |
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; cursor off |
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xor a |
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ld (CSRSW),a |
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; preload RomWBW rom into RAM Mapper segments |
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ld a,(nsegs) |
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ld b,a ; number of segment to load |
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ld a,4 ; starting segment |
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load_bank: push af |
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push bc |
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ld e,$0d ; set cursor to beginning of line |
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ld c,$02 ; CONOUT |
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call 5 |
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pop bc ; reload segment number |
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push bc |
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ld a,b |
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call dspNumA |
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pop bc |
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pop af ; reload segment number |
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out ($fe),a ; select ram segment in page 2 |
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ld (P2_SEG),a ; update system variable segment 2 (MSX-DOS 2) |
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inc a |
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; read rom bank data from file |
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push af |
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push bc |
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ld hl,16 ; read 16K data |
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ld de,romfile |
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ld c,$27 ; RDBLK |
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call 5 |
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or a ; error reading file? |
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jp nz,error_read ; nz=yes |
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pop bc |
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pop af |
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; next rom bank |
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djnz load_bank |
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; it's not necessary to close the file |
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; call H.TIMI 256 times to motor off floppy drives |
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di |
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xor a |
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mtcount: call H_TIMI ; H.TIMI handler saves register AF |
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dec a |
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jr nz,mtcount |
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; set CPU to Z80 mode |
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ld a,(CHGCPU) |
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cp $c3 |
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ld a,$80 ; set Z80 mode + switch Turbo LED indicator |
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call z,CHGCPU |
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; select RomWBW bootloader bank and start RomWBW |
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ld a,ROMWBW_SEG |
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out ($fc),a |
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inc a |
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out ($fd),a |
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jp $0 |
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; --------------------------------------------------------------------------- |
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; dspNumA - routine to display a value in A in ascii characters |
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; --------------------------------------------------------------------------- |
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dspNumA: ld l,a |
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ld h,0 |
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;ld bc,-100 |
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;call num1 |
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ld bc,-10 |
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call num1 |
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ld bc,-01 |
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num1: ld a,'0'-1 |
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num2: inc a |
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add hl,bc |
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jr c,num2 |
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sbc hl,bc |
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push hl |
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ld e,a |
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ld c,$02 ; CONOUT |
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call 5 |
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pop hl |
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ret |
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; --------------------------------------------------------------------------- |
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; Determine if a RAM mapper is available and what size it is |
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; Output: a = number of RAM mapper segments |
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; --------------------------------------------------------------------------- |
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MapperSize: ld hl,$8000 |
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; pass 1: test write/read segment 0 |
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ld a,1 |
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out ($fe),a ; set page 2 to segment 1 |
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ld b,(hl) ; save byte 1 |
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ld (hl),$aa ; write test value AA in segment 1 |
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xor a |
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out ($fe),a ; set page 2 to segment 0 |
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ld c,(hl) ; save byte 0 |
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ld (hl),$55 ; write test value 55 in segment 0 |
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inc a |
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out ($fe),a ; set page 2 to segment 1 |
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ld e,(hl) ; read test byte 1 in E |
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xor a |
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out ($fe),a ; set page 2 to segment 0 |
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ld (hl),c ; restore byte 0 |
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inc a |
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out ($fe),a ; set page 2 to segment 1 |
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ld (hl),b ; restore byte 1 |
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ld a,e ; AA=mapper 55=no mapper |
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cp $aa ; is mapper? |
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ld b,$00 ; set RAM segments to 0 |
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jr nz,_restore2 ; nz=no mapper |
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; pass 2: write test byte to all segments |
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_testpass2: ld a,b |
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out ($fe),a |
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ld a,(hl) |
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push af ; save byte on stack |
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inc sp ; " |
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ld (hl),$aa |
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inc b |
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jr nz,_testpass2 |
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; pass 3: determine number of valid ram segments |
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_testpass3: ld a,b |
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out ($fe),a |
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ld a,(hl) |
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cp $aa ; valid ram segment? |
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jr nz,_restore ; nz=no |
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ld a,$55 |
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ld (hl),a |
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cp (hl) ; 2nd test ok? |
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jr nz,_restore ; nz=no |
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inc b |
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jr nz,_testpass3 |
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dec b ; maximum segment number is 255 |
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; restore data saved on stack for each segment |
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_restore: ld c,$00 |
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_restore1: ld a,c |
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dec a |
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out ($fe),a |
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dec sp ; load byte on stack |
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pop af ; " |
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ld (hl),a |
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dec c |
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jr nz,_restore1 |
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; restore/set ram segment 1 in page 2 |
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_restore2: ld a,$01 |
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out ($fe),a |
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ld a,b |
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ret |
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; --------------------------------------------------------- |
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; Handle errors reading rom file |
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; --------------------------------------------------------- |
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error_open: ld de,t_open |
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jr error_end |
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error_read: pop bc |
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pop af |
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ld de,t_read |
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jr error_end |
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error_noram: ld de,t_noram |
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jr error_end |
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error_ramsize: ld de,t_ramsize |
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error_end: ld c,$09 ; STROUT |
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call 5 |
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jp 0 ; end program |
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t_message: .db "Loading RomWBW for MSX...",13,10,"$" |
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t_open: .db "Error opening msx-std.rom file$" |
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t_noram: .db "Error: no RAM mapper memory detected$" |
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t_ramsize: .db "Error: not enough RAM mapper memory$" |
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t_read: .db $0a,"Error reading msx-std.rom file$" |
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nsegs: .db 0 ; number of segments |
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romfile: .db 0,"MSX-STD ","ROM" ; fcb file |
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.fill 25,0 ; fcb variables |
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; ------------------------------------------------------------------------------ |
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LSIZE .EQU $-$c000 |
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.END |
H.J.Berends
4 months ago