Author Topic: RSX commands  (Read 2730 times)

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Offline kevin.c

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RSX commands
« on: 23:59, 11 March 15 »
I own my cpc6128 since late `80s. Over 25 years ago I put inside my cpc the SDOS ROM to handle DD 5.25" floppy.  This ROM has several  RSX commands, but  I do  remember nothing...  Is there any simple way to list all RSX'es and syntax?

Offline Bryce

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Re: RSX commands
« Reply #1 on: 00:17, 12 March 15 »
If it included a help command, I'd try |Help,7 if not you could install Utopia on a different ROM and use |Help,7 from there. Not sure if any of the disk based ROManagers list commands.

Alternatively, you could just go here: S-DOS - CPCWiki :)

Bryce.
« Last Edit: 00:19, 12 March 15 by Bryce »

Offline kevin.c

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Re: RSX commands
« Reply #2 on: 01:43, 12 March 15 »
Getting more and more interesting! No  commands work. The ROM introduce itself: 1986 SDOS 1.1 by SILIC Ltd.
It is possible, that somebody copying the ROM long long ago in a galaxy far far away has changed the ROM name...
That name is not known  to cpcwiki.
Looks that I have to dismount my cpc and read out the eprom.

Offline Bryce

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Re: RSX commands
« Reply #3 on: 10:19, 12 March 15 »
Can you dump the contents and upload the file here?

Bryce.

Offline kevin.c

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Re: RSX commands
« Reply #4 on: 20:26, 12 March 15 »
This is the dump of sdos ROM. It looks like it is protected in some way. There are 8 TTL + eprom on the board, and all TTL are without names!
I think some of TTLs must be  EXOR gates to decode ROM.

 [ Invalid Attachment ]
« Last Edit: 20:51, 12 March 15 by kevin.c »

Offline Bryce

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Re: RSX commands
« Reply #5 on: 23:23, 12 March 15 »
Ah, I thought it was just a ROM that you plugged in. Although from the dump it should be possible to reverse engineer it, because certain values have to be at certain addresses, so the bit swapping can be undone.

Bryce.

Edit: Hmm, just checked the bin file. The code is readable, so the Databit order hasn't been touched, only the address bits that have been jumbled.
« Last Edit: 23:27, 12 March 15 by Bryce »

Offline kevin.c

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Re: RSX commands
« Reply #6 on: 00:40, 13 March 15 »
Jumbled adress lines was also my first thought, but it would be to easy... and what for are so many IC on the board? Its a pity I can not identify them. Anyway eprom data lines don't come out directly to connector, but thru 2-3 ICes.
Bryce, have you ever met such hardware protection in any cpc peripherals?

Offline Bryce

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Re: RSX commands
« Reply #7 on: 00:41, 13 March 15 »
Yes, Brunword uses a similar system.

Some further info: At address &27C0 you find the word "Command" unscrambled. That's 7 bytes in a row in the correct order, which means that A0, A1 + A2 aren't manipulated. Now we are down to 11 possible signals that have been scrambled :) Time to check where the traces on the PCB go to.

Bryce.
« Last Edit: 00:49, 13 March 15 by Bryce »

Offline kevin.c

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Re: RSX commands
« Reply #8 on: 21:07, 13 March 15 »
This is the result of board investigation:
All EPROM address lines go as they should go, I mean A0>>A0......A13>>A13.
The descramble must be done on EPROM Data Bus, that how it goes:

D0: BUS+secret logic      (expl.: EPROM pin D0 goes to cpc Data Bus and some onboard IC)
D1: BUS+secret logic
D2: BUS+secret logic
D3:         secret logic only
D4: BUS+secret logic
D5:         secret logic only
D6: BUS+secret logic
D7: BUS+secret logic

Possible that  D3 and D5 are logically processed by address lines.
I can feel next chalange...

Latest news:
EPROM lines D3 and D5 go to IC with the structure like typical 4-gates TTL. If I presume that this IC is 4-EXOR gate, the D3 is exored with A4, and D5 is exored with A2. I think this is the solution of scramble formula of the ROM.
Next try is to write a script to transcode ROM with above formula.
 
« Last Edit: 22:25, 13 March 15 by kevin.c »

Offline KaosOverride

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Re: RSX commands
« Reply #9 on: 13:55, 14 March 15 »
Why not use any of the ROM dumper programs to create a .ROM fileat thje CPC and transfer it to the PC from disk?

At the worst scenario, maybe only the start of the ROM is usable, there are defined some subpages in the ROM, and only the first is accesible, but holds the decode algoritm to access rest of ROM... If is a passive protection, then you hace the full dump...

Just for try...
KaosOverride · GitHub
MEGA Amstrad Public Amstrad folder

Offline kevin.c

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Re: RSX commands
« Reply #10 on: 16:50, 14 March 15 »
This ROM board is old amateur construction, with wiped out IC names.. It does not work corectly when I touched it to dump the EPROM. ???
My idea is to put this ROM content to MegaFlesh, but at first I have to decode it correctly. That's why  I investigate the board.
Anyway it's just a fun!

Offline KaosOverride

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Re: RSX commands
« Reply #11 on: 00:02, 15 March 15 »
So dumping it from the CPC with a rom reader software don't work? Weird  :P
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Offline gerald

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Re: RSX commands
« Reply #12 on: 00:15, 15 March 15 »
This ROM board is old amateur construction, with wiped out IC names.. It does not work corectly when I touched it to dump the EPROM. ???
My idea is to put this ROM content to MegaFlesh, but at first I have to decode it correctly. That's why  I investigate the board.
Anyway it's just a fun!
Can you post picture of the board component and solder side ?
We might guess the IC from layout (if all track are visible) and ROM content you already dumped.

Offline kevin.c

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Re: RSX commands
« Reply #13 on: 14:12, 15 March 15 »
So dumping it from the CPC with a rom reader software don't work? Weird  :P
Excuse me, may be I was not so precise. I took out the eprom, and dumped it with external willem programmer.
Can you advise please what  software should I use to read this eprom from cpc?
Gerald, of course I can post the pictures of the board, but it will be defficult to trace out all tracks from pictures only, and I do not want to bother you with such unnoying job..  ::)

Offline KaosOverride

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Re: RSX commands
« Reply #14 on: 18:33, 15 March 15 »
Some time ago, I used the ROMGET.BAS program from CPCEMU.
http://www.genesis8bit.com/frontend/emulator/cpcemu15.zip

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Offline kevin.c

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Re: RSX commands
« Reply #15 on: 23:51, 15 March 15 »
Thank you, as soon as I can I will try it!

Offline Gryzor

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Re: RSX commands
« Reply #16 on: 22:29, 16 March 15 »
Can you post a photo for retro pr0n's sake? :)

Offline kevin.c

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Re: RSX commands
« Reply #17 on: 23:00, 18 March 15 »
I solved all problems. The board works well. The problem was with EPROM. It failed after 29 years. I tried to reprogramm it, but there were several errors, new EPROM works fine. I was lucky to read it correctly anyway. KaosOverride thank you, ROMGET.BAS done well.
I do not know the origin of my ROM, but studying cpcwiki I found that it is modyfied english version of Vortex V-DOS!  VDOS - CPCWiki
I wonder who changed the ROM name... :D
For this moment my old 5,25" drive is waiting for repair. The drive  - model hd-55dx - has no integrated controller, but 11 ICs. One of them has failed. 
Working and decoded copy of SDOS aka V-DOS:
  [ Invalid Attachment ]

Offline KaosOverride

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Re: RSX commands
« Reply #18 on: 01:27, 19 March 15 »
Good news!!!

Glad to help you!! 8)
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