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# Titan /// plus // Emulation patch info for Selector
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This details the patches I did to allow the Titan ///+// card's emulation to be started from Selector ///
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Selector /// includes an install program that sets up the normal Apple II emulation onto a harddisk to allow launching without the need for a floppy. Support for the Titan cards was never provided.
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After Selector /// has been installed, and the Emulation installer has been run. The following is the disk structure and files created.
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```
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-PROGRAMS
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-APPLE2
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-INSTALL.APPLE2 - This is the Selector Apple2 Emulation install program
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SOS.INTERP - This is the Loader and config code for the Apple2 Emulation
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it refers and loads the APPLE2.INTERPS and APPLE2.DATA files
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APPLE2.INTERPS This holds the slot 5-7, Integer and Applesoft BASIC ROMs
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APPLE2.DATA This looks like it holds the current config settings selected for the emulation
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```
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The Titan III+II card is basically a 128k saturn language card with an Apple II game port on it. The whole thing is enabled by setting the A3 to 1MHz and then performing an access to the Card slot rom (I/O select). The card then stays enabled while the speed is kept at 1Mhz. Once you switch back to 2MHz, the card deselects.
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I did some fishing around on the III+II disk, and found is has a lda CX00 for each slot, so this allows the disk to work with the card in any slot.
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```
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lda $c100
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lda $c200
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lda $c300
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lda $c400
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```
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Using the diassembly of the A2 emulation available here https://github.com/brouhaha/a3a2em, I found that the SOS.INTERP file mentioned above has the init code in it. After some more digging, I came up with this comparison of the differences in code between the standard and Titan versions.
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```
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Offset in Original ///+II
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SOS.INTERP
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0471 a9 00 lda #$00 a9 00 lda #$00
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0473 8d f2 03 sta $03f2 8d f2 03 sta $03f2
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0476 a9 e0 lda #$e0 a9 00 lda #$00
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0478 8d f3 03 sta $03f3 8d f4 03 sta $03f4
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047b 20 6f fb jsr $fb6f ad 00 c1 lda $c100 ; enable ///+II card
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047e ad 51 c0 lda $c051 ad 00 c2 lda $c200
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0481 ad 56 c0 lda $c056 ad 00 c3 lda $c300
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0484 ad 54 c0 lda $c054 ad 00 c4 lda $c400
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0487 ee f4 03 inc $03f4 ad 84 c0 lda $c084
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048a 58 cli 4c 62 fa jmp $fa62 ; jmp A2 reset
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048b 4c 62 fa jmp $fa62 ; jmp A2 reset
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```
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Now to patch this in some how. The approach I took was to copy and rename the three selector files for the standard emulation disk to create a set for the Titan card.
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```
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SOS.INTERP -> SOS3P2.INTERP
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APPLE2.INTERPS -> APP3P2.INTERPS
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APPLE2.DATA -> APP3P2.DATA
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```
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Then I used a hex editor to change the filenames in the SOS3P2.INTERP file to reference the new names APP3P2.INTERPS & APP3P2.DATA
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And finally update the init code in the SOS3P2.INTERP file as detailed above. See the image of the changes in red.
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I then found that due to the A3 having the disk controller in Slot6, and no slot7 to put a block storage device in, then its difficult to boot from one in Slot 1-4 directly.
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To support this, I wanted to provide another version and patch the Autostart rom to scan the slots the other way around. I also wanted to apply the patch to only check for 3 ID bytes, and not 4 to allow block devices to boot. For this I created another set of files:
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```
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SOS3P2.INTERP -> SOS3P26.INTERP
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APP3P2.INTERPS -> AP3P26.INTERPS
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APP3P2.DATA -> AP3P26.DATA
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```
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Then I investigated which file has the ROMs, and came up with this map for APPLE2.INTERPS file
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```
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file offset
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0000 - 00ff Slot5 rom - applesoft setup?
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0100 - 01ff Slot6 rom - applesoft setup?
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0200 - 02ff Slot7 rom - applesoft setup?
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0300 - 03ff Slot5 rom - integer setup?
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0400 - 04ff Slot6 rom - integer setup?
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0500 - 05ff Slot7 rom - integer setup?
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0600 - 0dff D0 - applesoft
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0e00 - 15ff D8 - applesoft
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1600 - 1dff E0 - applesoft
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1e00 - 25ff E8 - applesoft
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2600 - 2dff F0 - applesoft
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2e00 - 35ff F8 - Autostart
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3600 - 3dff D0 - programmers aid
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3e00 - 45ff D8 - blank
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4600 - 4dff E0 - integer
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4e00 - 55ff E8 - integer
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5600 - 5dff F0 - integer
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5e00 - 65ff F8 - Autostart?
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```
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This was the required patch to apply
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```
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FAB4 A9 *C0 LDA #$C0 ; ; LOAD LOW SLOT -1
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FAB6 86 00 STX LOC0 ; ; SETPG3 MUST RETURN X=0
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FAB8 85 01 STA LOC1 ; ; SET PTR H
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FABA A0 *05 SLOOP: LDY #5 ;Y is byte ptr, check 3 ID bytes instead of 4
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FABC *E6 01 INC LOC1
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FABE A5 01 LDA LOC1
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FAC0 C9 *C7 CMP #$C7 ; ; AT LAST SLOT YET?
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FAC2 F0 D7 BEQ FIXSEV ; ; YES AND IT CAN'T BE A DISK
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FAC4 8D F8 07 STA MSLOT
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FAC7 B1 00 NXTBYT: LDA (LOC0),Y ; ; FETCH A SLOT BYTE
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FAC9 D9 01 FB CMP DISKID-1,Y ; ; IS IT A DISK ??
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FACC D0 EC BNE SLOOP ; ; NO, SO NEXT SLOT DOWN
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FACE 88 DEY
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FACF 88 DEY ; YES, SO CHECK NEXT BYTE
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FAD0 10 F5 BPL NXTBYT ; ; UNTIL 3 BYTES CHECKED
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FAD2 6C 00 00 JMP (LOC0) ; ; GO BOOT...
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```
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and the changes in the AP3P26.INTERPS:
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```
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offset
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30b5 c8 -> c0
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30bb 07 -> 05
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30bc c6 -> e6
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30c1 c0 -> c7
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60b5 c8 -> c0
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60bb 07 -> 05
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60bc c6 -> e6
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60c1 c0 -> c7
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```
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Once these files were all prepared, the last step was to add some new menu entries into Selector to allow these Interpreters to be run directly.
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