Uncovering the R800

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By Grauw

Enlighted (8073)

Grauw's picture

14-12-2018, 14:25

lintweaker wrote:

@Grauw,
Forgot to ask/mention, just popped up again. If I recall correctly those LDCTL instructions are privileged instructions. Could the R800 be running in non-privileged mode? (if they implemented that stuff at all, still likely the only took what the needed from the Z800/Z280).

I think any CPU with system / user modes must boot up in system mode. I looked for any special instructions in the CPU switching parts of the disassembled turboR BIOS but I didn’t see any, so even if it supports a user mode it doesn’t seem likely to me that it’s been switched to it.

By Edevaldo

Expert (116)

Edevaldo's picture

14-12-2018, 20:50

Quote:

Grauw wrote:
I think any CPU with system / user modes must boot up in system mode.

I certainly agree. It makes no sense to do otherwise and it makes little sense that the user mode code could change its state freely. But...

The turbo-r has 2 ROM chips, providing 1.5MBytes. This made me wonder if the thing is not starting at a different point in those ROMs with some privileged code that sets up the environment, maps the memory as a regular MSX would, jumps into a "Z80 like" user mode and never looks back.

If we could understand how all the memory we can see in the turbo-R is mapped into those chips it could help. If we find any region of those chips that is not visible...

Interesting the DMA EOP pin also exist in the Z800/R280. But the DMA in the R800 seems to be only 2 channels. As the pins are not connected, it may still be useful for memory to memory transfers.

I also wonder that the FTREN pin is good for. It seems to enable something...

By erpirao

Paladin (880)

erpirao's picture

14-12-2018, 20:48

in blue msx the roms are:
KAnji: 256KB
MSXDOS23: 64KB
MSXKANJI: 32KB
MSXTR: 32KB
MSXTREXT: 16KB
MSXTRMUS: 16KB
MSXTROPT: 16KB
XBASIC21: 16KB
MOONSOUND: 2MB

without moonsound: 448KB

By Edevaldo

Expert (116)

Edevaldo's picture

14-12-2018, 20:56

Quote:

on 14-12-2018, 20:48, erpirao wrote:

in blue msx the roms are:
KAnji: 256KB
MSXDOS23: 64KB
MSXKANJI: 32KB
MSXTR: 32KB
MSXTREXT: 16KB
MSXTRMUS: 16KB
MSXTROPT: 16KB
XBASIC21: 16KB
MOONSOUND: 2MB

without moonsound: 448KB

This is significantly less ROM than the Turbo-R has. We cannot forget MSX-View related stuff that the emulator seems to be missing.

But I do not think any emulator would have the full ROMs if there are any part of them that would contain R800 supposedly privileged code. We probably need to dump all pages of all slots in the machine and see if this adds up to what the memories contain.

By Edevaldo

Expert (116)

Edevaldo's picture

14-12-2018, 21:03

Quote:

I also wonder that the FTREN pin is good for. It seems to enable something...

It seems to be related to the speed of the LDDR/LDIR instructions. The manual seems to call this pin "Fast LDDR/LDIR enable (unused)".

By Edevaldo

Expert (116)

Edevaldo's picture

14-12-2018, 21:09

Does anybody understands enough of Japanese to make sense of the description given to the REFEN pin on page 36 of the turbo-r manual?

Initially I thought it would be related to memory refresh. But the translation I get is that it enables non-used internal blocks. ????

By erpirao

Paladin (880)

erpirao's picture

14-12-2018, 21:44

Edevaldo wrote:
Quote:

on 14-12-2018, 20:48, erpirao wrote:

in blue msx the roms are:
KAnji: 256KB
MSXDOS23: 64KB
MSXKANJI: 32KB
MSXTR: 32KB
MSXTREXT: 16KB
MSXTRMUS: 16KB
MSXTROPT: 16KB
XBASIC21: 16KB
MOONSOUND: 2MB

without moonsound: 448KB

This is significantly less ROM than the Turbo-R has. We cannot forget MSX-View related stuff that the emulator seems to be missing.

But I do not think any emulator would have the full ROMs if there are any part of them that would contain R800 supposedly privileged code. We probably need to dump all pages of all slots in the machine and see if this adds up to what the memories contain.

msxturboR a1GT Roms (Bluemsx=
a1gtbios: 26
a1gtdos: 39
a1gtext: 12
a1gtfirm: 1104
a1gtkdr: 25
a1gtkfn: 139
a1gtmus: 11
a1gtopt: 2

without a1gt firmware (msx-view): 254

By Edevaldo

Expert (116)

Edevaldo's picture

17-12-2018, 18:45

I was looking into FS-A1ST motherboard pictures in the internet and noticed that some of them have 2 Fujitsu ROMs, one 512k and the other 1M. But some have 3 ROMs, 512kBytes each. Also from Fujitsu.

The ROM address decoding is done by S1990. This may mean 1 of two things. The S1990 ROM decoding may be programmable and initialized by the ROM at startup. Or, the ROM decoding is fixed, each ROM is ocupying 1M space, and the CPU is looking for that 3rd ROM at a different address than the 2nd half of the 1M ROM that occupies the IC18 spot in most ST pictures I saw. In the 3 ROM pcb picture I saw, the third ROM occupies IC19 spot.

3 ROMs ST link.

It is an interesting information to keep in mind when investigating the R800.

By erpirao

Paladin (880)

erpirao's picture

21-12-2018, 16:36

Looking at the similarities, how would it be difficult to make a translator r800-> z280?
and the other way around?

By erpirao

Paladin (880)

erpirao's picture

21-12-2018, 16:37

Edevaldo wrote:

I was looking into FS-A1ST motherboard pictures in the internet and noticed that some of them have 2 Fujitsu ROMs, one 512k and the other 1M. But some have 3 ROMs, 512kBytes each. Also from Fujitsu.

The ROM address decoding is done by S1990. This may mean 1 of two things. The S1990 ROM decoding may be programmable and initialized by the ROM at startup. Or, the ROM decoding is fixed, each ROM is ocupying 1M space, and the CPU is looking for that 3rd ROM at a different address than the 2nd half of the 1M ROM that occupies the IC18 spot in most ST pictures I saw. In the 3 ROM pcb picture I saw, the third ROM occupies IC19 spot.

3 ROMs ST link.

It is an interesting information to keep in mind when investigating the R800.

very interesting, now that I remember, my ST also has 3 Rom chips.

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