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Fixing the Oric Giga Demo

Posted: Sun Apr 06, 2014 11:19 am
by Dbug
The original discussion is on

The idea is to fix the Oric Giga Demo, which suffered from a number of issues:
- Our loader was not mature at the time, so it was crashing a lot, we had to use a hacked Sedoric loader instead, resulting in a first a very slow loading time in some parts, and second the fact we could not use the overlay memory means the demo has no music at all
- The floppy builder was not very mature either, and as a result there are some bugs on the disk, like the message "Lifeiis short", the double "ii" is a bug caused by the tool writing datas incorrectly to the disk.
- Some other glitches, like the 60hz switch during the rotozoom, which causes some screens to go berzerk
- The overly visible red line on the scrolling picture (because at the time we did not have any conversion tool that could handle pictures taller than the screen)
- The broken rotating thingies which were supposed to be a 3D Studio animation, but it got broken during the packing
- The end logo which was brutally converted and looks like crap
- EDIT: Apparently it does not run on ORIC1 either, it calls Oric Atmos ROM functions such as HIRES

The idea is to fix the demo, at a minimum that would involve repackaging all of it using the new loader, which would in turn leave the overlay memory free, which would allow me to put a music.

If I can find ways to fix the rest without spending the rest of my life on it (hint: I do not have the source codes...), I will try to fix some of the most glaring bugs.

And since it looks like the various development diaries seem to interest people, I will document the progress in this thread.
Don't expect fast progress though, I will probably spend an hour here, an hour there, so it may take months :)

Re: Fixing the Oric Giga Demo

Posted: Sun Apr 06, 2014 11:29 am
by Dbug
First step: Extraction of the actual Sedoric files.

When you boot the demo you can CTRL+C, which shows easily that there are only two real files on the floppy:

The first one is a basic program which shows the intro page and then loads the second one.

Code: Select all

 1 POKE #BBA4,0
 2 POKE #26A,14
 10 CLS
 20 PAPER0
 30 INK 7
 40 PRINT"======================================"
 50 PRINT CHR$(27);"T";
 70 PRINT CHR$(27);"A";
 75 PRINT CHR$(27);"J";
 90 PRINT CHR$(27);"T";
 100 PRINT CHR$(27);"C";
 110 PRINT CHR$(27);"J";
 130 PRINT"======================================"
 135 PRINT""
 140 PRINT"Presented and rated #1 at the VIP3"
 150 PRINT"July 2001"
 160 PRINT""
 189 PRINT"
 190 PRINT"--------------------------------------"
 191 PRINT""
 200 PRINT"Code : Dbug, Jede, Twilighte"
 205 PRINT
 210 PRINT"Gfx : Eaks, Twilighte"
 215 PRINT
 220 PRINT"Music : Twilighte"
 235 PRINT
 240 PRINTCHR$(96);:PRINT" Defence-Force 2001"
 1000 PRINT"======================================" 
 1009 PRINT CHR$(27);"T";
 1010 PRINT CHR$(27);"A";
 1020 PRINT CHR$(27);"N";
 1033 PRINT CHR$(27);"T";
 1034 PRINT CHR$(27);"C"; 
 1035 PRINT CHR$(27);"N";
 2000 PRINT"======================================"
 2020 GET A$
 2030 !DISK.COM
that one is easy to rip out:
(the ,N option is used to disable the auto-start)

For the second one, we need first to find the start and end address:
050A 0800 41 050A
Now that we know that it loads and starts from 50A and finishes in 800, we can save it as well:
After some inspection in the debugger, it appears to be 100% assembler code, which fortunately is much easier to disassemble that C, so the next step is to disassemble it and add readable labels.

My disassembler of choice is from the C64 people and is named Regenerator. Unfortunately it does not know the Oric file format, so I need to convert the file to C64 format, which basically means removing the Oric header,
%osdk%/bin/header -h0 DISK.TAP disk.prg
and then adding the C64 header which is just two bytes containing the load address!
patching_header.png (31.84 KiB) Viewed 12089 times
Does not look very readable, but now we can load it in Regenerator and start abusing of the "add labels" feature.
regenerator_loader.png (146.64 KiB) Viewed 12089 times
And that's basically all I have for today :)

Re: Fixing the Oric Giga Demo

Posted: Sun Apr 06, 2014 12:12 pm
by Dbug
I'm done with the disassembling of the loader:

Code: Select all

index_logo = $4F
; **** USER LABELS **** 
current_sector = $0200
current_track = $0201
load_counter = $0202
current_drive = $0203
buffer_low = $0204
buffer_high = $0205
file_index = $0206
sedoric_swap_overlay = $04F2
sedoric_romram_flag = $04FB
run_0800 = $0800
run_1000 = $1000
run_765a = $765A
sedoric_drive = $C000
sedoric_track = $C001
sedoric_sector = $C002
sedoric_buffer_low = $C003
sedoric_buffer_high = $C004
rom_hires = $EC33
rom_init_charsets = $F8D0
sedoric_read_sector = $FFB8

        * = $050A

        JSR initialize
        LDX #$00
        JSR load_file
        JSR run_1000
        LDX #$01
        JSR load_file
        JSR run_0800
        LDY #$FF
loop_wait JSR wait
        BNE loop_wait
        LDX #$05
        JSR load_file
        JSR run_0800
        JSR rom_hires
        LDX #$03
        JSR load_file
        JSR run_0800
        LDX #$02
        JSR load_file
        JSR run_0800
        JSR rom_init_charsets
        JSR rom_hires
        LDX #$04
        JSR load_file
        JSR run_0800
        LDX #$06
        JSR load_file
        LDA #$00
        STA index_logo
logo_patch_index   =*+$01
loop_load_logo LDX #$0A
        JSR load_file
        JSR run_0800
        INC index_logo
        INC logo_patch_index
        JSR wait
        JSR wait
        LDX index_logo
        CPX #$33
        BNE loop_load_logo
        LDX #$07
        JSR load_file
        JSR run_0800
        LDX #$08
        JSR load_file
        JSR run_0800
        LDX #$09
        JSR load_file
        JSR run_0800
        JSR rom_hires
        LDX #$3D
        JSR load_file
        JSR run_765a

load_file STX file_index
        JSR fetch_file_info
load_loop JSR find_next_sector
        INC current_sector
        DEC load_counter
        BNE load_loop
        JSR find_next_sector

fetch_file_info LDX file_index
        LDA table_sectors,X
        STA current_sector
        LDA table_drives
        STA current_drive
        LDA table_tracks,X
        STA current_track
        LDA table_addresses_low
        STA buffer_low
        LDA table_addresses_high,X
        STA buffer_high
        LDA table_sector_count,X
        STA load_counter

find_next_sector JSR load_sector
        INC buffer_high
        LDA current_sector
        CMP #$11
        BNE same_track
        INC current_track
        LDA #$00
        STA current_sector
same_track RTS 

wait    PHA 
        LDY #$00
incrementation2 LDX #$00
incrementation22 INX 
        BNE incrementation22
        BNE incrementation2

initialize LDA #$00
        STA file_index
        LDA #$86
        STA sedoric_romram_flag

load_sector JSR sedoric_swap_overlay
        LDA buffer_low
        STA sedoric_buffer_low
        LDA buffer_high
        STA sedoric_buffer_high
        LDA current_drive
        STA sedoric_drive
        LDA current_track
        STA sedoric_track
        LDA current_sector
        STA sedoric_sector
        JSR sedoric_read_sector
        JSR sedoric_swap_overlay

table_drives .BYTE $00
table_sectors .BYTE $01,$05,$05,$06,$07,$11,$0D,$07
        .BYTE $0F,$11,$07,$0F,$06,$0E,$01,$09
        .BYTE $11,$08,$10,$07,$0F,$06,$0E,$05
        .BYTE $0D,$04,$0C,$03,$0B,$02,$0A,$01
        .BYTE $09,$11,$08,$10,$07,$0F,$06,$0E
        .BYTE $05,$01,$09,$11,$08,$10,$07,$0F
        .BYTE $06,$0E,$05,$0D,$04,$0C,$03,$0B
        .BYTE $02,$0A,$01,$09,$11,$08,$02
table_tracks .BYTE $80,$84,$86,$88,$90,$90,$91,$92
        .BYTE $95,$9C,$A5,$A5,$A6,$A6,$07,$07
        .BYTE $07,$08,$08,$09,$09,$0A,$0A,$0B
        .BYTE $0B,$0C,$0C,$0D,$0D,$0E,$0E,$0F
        .BYTE $0F,$0F,$10,$10,$11,$11,$12,$12
        .BYTE $13,$15,$15,$15,$16,$16,$17,$17
        .BYTE $18,$18,$19,$19,$1A,$1A,$1B,$1B
        .BYTE $1C,$1C,$1D,$1D,$1D,$1E,$24
table_sector_count .BYTE $47,$21
        .BYTE $22,$88,$09,$0C,$0A,$3A,$78,$8E
        .BYTE $07,$07,$07,$07,$07,$07,$07,$07
        .BYTE $07,$07,$07,$07,$07,$07,$07,$07
        .BYTE $07,$07,$07,$07,$07,$07,$07,$07
        .BYTE $07,$07,$07,$07,$07,$07,$07,$07
        .BYTE $07,$07,$07,$07,$07,$07,$07,$07
        .BYTE $07,$07,$07,$07,$07,$07,$07,$07
        .BYTE $07,$07,$07,$5F,$0E
table_addresses_low .BYTE $00
table_addresses_high .BYTE $10,$08,$08,$08,$08,$08,$08,$08
        .BYTE $08,$08,$0A,$0A,$0A,$0A,$0A,$0A
        .BYTE $0A,$0A,$0A,$0A,$0A,$0A,$0A,$0A
        .BYTE $0A,$0A,$0A,$0A,$0A,$0A,$0A,$0A
        .BYTE $0A,$0A,$0A,$0A,$0A,$0A,$0A,$0A
        .BYTE $0A,$0A,$0A,$0A,$0A,$0A,$0A,$0A
        .BYTE $0A,$0A,$0A,$0A,$0A,$0A,$0A,$0A
        .BYTE $0A,$0A,$0A,$0A,$0A,$60
        .BYTE $DC,$00,$00
So basically what this loader do is to use the various tables that contain information about where the files are on disk to call the Sedoric function that loads sectors.

Some of the demo screens load in $800 (just after the loader itself), some in $1000, and for some strange reason the last part is loaded in $765a

As you can see, there are also calls to the overlay switch code (in page 4), HIRES and CHARSET initialization (ATMOS Rom calls).

The loop in the middle is the one that charges all the logos shown during the greetings. I always wondered why it was so slow, I guess the two jsr wait may have something to do with it.

I guess the next step is to find a way to use the sector/track/size table to extract the binary blobs from the DSK file, and then convert all that to use the new FloppyBuilder and see if it runs.

Re: Fixing the Oric Giga Demo

Posted: Sun Apr 06, 2014 2:20 pm
by Dbug
And more good news, I managed to locate the original picture used on the poster scroll, did a naive conversion with the Img2Oric mode, looks much better already :)
poster-240x320-f6.png (13 KiB) Viewed 12059 times
The source picture was 540x720, I reduced it to 240x320, and then had to fix PictConv because the Img2Oric algorithm would not accept a picture taller than 200 pixels (the fixed version is in SVN, will be in the next OSDK publish).

Re: Fixing the Oric Giga Demo

Posted: Sun Apr 06, 2014 5:33 pm
by ibisum
I can't imagine what the world of Oric would have been like if we'd had such quality pictures to drool over way back then .. ;)

Re: Fixing the Oric Giga Demo

Posted: Sun Apr 06, 2014 8:53 pm
by Hialmar
Thanks a lot for this post.

It is really interesting to find out about this wonderful disassembler tool from the C64.

I have a plan of porting "L'Aigle d'Or" to C and this will help me a lot I think ;)