First public commit.

lenser/viewer/cart.s

@@ -0,0 +1,177 @@
+; lenser -- C64 cartridge viewer (runs from ROM at $8000), fully self-contained.
+;
+; Unlike the disk viewer (a PRG at $0801 with the picture appended), this runs
+; from a 16K cartridge.  It copies the image data block -- appended after this
+; code in ROM -- down to $2000 (same layout the disk viewer wants, bitmap at
+; $2000, screen $3F40, and for multicolor colram $4328 + bg $4710), programs the
+; VIC, and holds the picture.  It uses NO KERNAL/IRQ services (a 16K cart hides
+; BASIC and the autostart entry runs before the KERNAL fully initialises), so it
+; polls the hardware directly -- CIA1 for the keyboard, the raster for timing.
+;
+; #defines set by viewer/assemble.py --
+;   MCMODE   0 = hires, 1 = multicolor
+;   NPAGES   number of 256-byte pages of image data to copy
+;   WAITMODE 0 forever / 1 until a key / 2 about WAITSECS seconds
+;   WAITSECS, RATE (frames per second, 50 PAL / 60 NTSC)
+;
+; assembled by viewer/assemble.py via xa
+
+        * = $8000
+        .word cold              ; cold-start vector
+        .word cold              ; NMI / warm vector
+        .byte $c3,$c2,$cd,$38,$30   ; CBM80 autostart signature
+
+SRC = $fb
+DST = $fd
+CNT = $02               ; 16-bit frame countdown (seconds mode)
+
+cold:
+        sei
+        ldx #$ff
+        txs
+        cld
+
+        ; map the standard memory layout so BOTH halves of the 16K cart are
+        ; visible -- ROML $8000-$9FFF and ROMH $A000-$BFFF (needs HIRAM=1) -- plus
+        ; I/O at $D000.  Set the data latch ($01) BEFORE the DDR ($00): on a cart
+        ; cold-start the latch may be low while the DDR is all-inputs (so the port
+        ; reads the correct map via pull-ups). Enabling the DDR first would drive
+        ; that low latch onto the port, bank ROML out, and crash the next fetch
+        ; (this is exactly what failed in VICE).
+        lda #$37
+        sta $01                 ; LORAM+HIRAM+CHAREN = ROML, ROMH, I/O, KERNAL
+        lda #$2f
+        sta $00                 ; now enable the port outputs
+
+        ; VIC bank 0 ($0000-$3FFF) so the VIC sees our bitmap at $2000
+        lda #$3f
+        sta $dd02               ; CIA2 port A bits 0-5 = output
+        lda #$c7
+        sta $dd00               ; bank 0 (bits 0-1 = 11)
+
+        lda #$0b
+        sta $d011               ; blank during setup
+
+        ; ---- copy NPAGES of image data from ROM (datasrc) to $2000 ----
+        lda #<datasrc
+        sta SRC
+        lda #>datasrc
+        sta SRC+1
+        lda #$00
+        sta DST
+        lda #$20
+        sta DST+1
+        ldx #NPAGES
+        ldy #$00
+dcopy:
+        lda (SRC),y
+        sta (DST),y
+        iny
+        bne dcopy
+        inc SRC+1
+        inc DST+1
+        dex
+        bne dcopy
+
+        ; ---- copy screen RAM $3F40 -> $0400 ----
+        lda #$40
+        sta SRC
+        lda #$3f
+        sta SRC+1
+        lda #$00
+        sta DST
+        lda #$04
+        sta DST+1
+        jsr copy1024
+
+#if MCMODE == 1
+        ; ---- copy colour RAM $4328 -> $D800 ----
+        lda #$28
+        sta SRC
+        lda #$43
+        sta SRC+1
+        lda #$00
+        sta DST
+        lda #$d8
+        sta DST+1
+        jsr copy1024
+#endif
+
+        ; ---- program the VIC-II ----
+        lda #$00
+        sta $d020               ; border black
+#if MCMODE == 1
+        lda $4710
+        sta $d021               ; background colour
+        lda #$d8
+        sta $d016               ; multicolor on
+#endif
+#if MCMODE == 0
+        lda #$c8
+        sta $d016               ; hires
+#endif
+        lda #$18
+        sta $d018               ; screen $0400, bitmap $2000
+        lda #$3b
+        sta $d011               ; bitmap mode, display on
+
+        ; ---- hold the picture ----
+#if WAITMODE == 0
+forever:
+        jmp forever
+#endif
+
+#if WAITMODE == 1
+        lda #$ff
+        sta $dc02               ; CIA1 port A = output (column select)
+        lda #$00
+        sta $dc03               ; CIA1 port B = input  (row read)
+        sta $dc00               ; drive all keyboard columns low
+kwait:
+        lda $dc01               ; rows; $FF = no key, any key pulls a row low
+        cmp #$ff
+        beq kwait
+        jmp $fce2               ; reset (a 16K cart can't return to BASIC)
+#endif
+
+#if WAITMODE == 2
+        lda #<(WAITSECS*RATE)
+        sta CNT
+        lda #>(WAITSECS*RATE)
+        sta CNT+1
+sloop:
+sw1:
+        lda $d012
+        cmp #$fa
+        bne sw1                 ; wait until raster reaches line 250
+sw2:
+        lda $d012
+        cmp #$fa
+        beq sw2                 ; wait until it leaves -> one frame elapsed
+        lda CNT
+        bne sdec
+        dec CNT+1
+sdec:
+        dec CNT
+        lda CNT
+        ora CNT+1
+        bne sloop
+        jmp $fce2               ; reset
+#endif
+
+copy1024:
+        ldx #4
+        ldy #0
+c1k:
+        lda (SRC),y
+        sta (DST),y
+        iny
+        bne c1k
+        inc SRC+1
+        inc DST+1
+        dex
+        bne c1k
+        rts
+
+datasrc:
+        ; image data block appended here by the packager