Spectravideo SVI-3x8 support in openMSX

By Manuel

Ascended (12816)

Manuel's picture

11-09-2016, 12:00

Back in 2012, Tomas Karlsson submitted a patch to openMSX to add support for Spectravideo SVI-3x8. At that time, Wouter picked it up and discussed a bit with him, until we didn't hear anything from him anymore.
The code was put in a separate branch a few months ago. With NYYRIKKI we fixed some details, but after that it got stalled again.

Development of this is still stalled, but we did decide to merge the branch for Spectravideo support into the master branch, which means what we implemented so far is now available in the openMSX development builds at http://openmsx.fixato.net/

Limitations:
- SVI CAS files are not supported (you'll have to convert them to WAV or use WAV images)
- floppy drive not really tested, not sure if it works
- SVI-328 config has an FDC built in, which isn't realistic I think. For some reason it also has 64kB RAM in both slot 2 and 3.
- Nothing (absolutely nothing) is done to prevent the user to combine SVI and MSX hardware.

Still, now you can play with it and help us to improve it.

Who will help out?

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By NYYRIKKI

Enlighted (4426)

NYYRIKKI's picture

11-09-2016, 12:58

Manuel wrote:

The code was put in a separate branch a few months ago. With NYYRIKKI we fixed some details, but after that it got stalled again.

I think the major reason is that there is no anything wrong with it... Rest of the problems are related to interfacing between SVI and PC and I have no really skills to help with that.

Quote:

Development of this is still stalled, but we did decide to merge the branch for Spectravideo support into the master branch

\o/

Quote:

- floppy drive not really tested, not sure if it works

Yes... DSK-files are not supported. DMK... there are no any tools to create them... SVI is a bit pain in the ass as it formats the first side first track with FM and rest of the disk with MFM encoding. This makes dumping a bit hard since PCs or MSX's didn't ever have hardware support for FM encoding AFAIK.

Quote:

- SVI-328 config has an FDC built in, which isn't realistic I think. For some reason it also has 64kB RAM in both slot 2 and 3.

Well... SVI BIOS does not search for RAM as MSX does, so extra RAM just sits there doing absolutely nothing... unless some program really happens to find it... Extra 64KB+64KB is the maximum amount of memory that the computer can have, so it kind of makes sense. Other possibility would be ignoring the writes to these areas, but that might cause the program doing that to crash... No sense to block this possibility although maxed out machine is quite unlikely in real life. There is also not really any other use for these "slots" either... Nothing is executed, read or initialized from them.

By Manuel

Ascended (12816)

Manuel's picture

11-09-2016, 13:17

We try to make accurate configuration files of the machines how they came out of the factory. This is thus currently not the case for the 328-config... (perhaps we should say Boosted Spectravideo SVI-328 ;-) But as it's completely not supported discern between MSX and SVI extensions, it may be good enough for now.

By Manuel

Ascended (12816)

Manuel's picture

11-09-2016, 21:35

Oh, I remember, disk support works indeed, as long as you are somehow able to create a DMK image Smile I think we hacked DSK2DMK for that to get something working.

By NYYRIKKI

Enlighted (4426)

NYYRIKKI's picture

12-09-2016, 12:52

Manuel wrote:

But as it's completely not supported discern between MSX and SVI extensions, it may be good enough for now.

Yes, I agree. The whole idea of "slots" is quite different on SVI, because it does not have MSX type "slot select" signal... Game cartridge connector is a place for program ROM that can start automatically, it can't contain I/O devices, but it can use up to 3 "slot select" signals depending of memory area. (11/ROMEN0/ROMEN1)

Rest of the "slots" (=where you can plug extensions) are with different pinout and from the computer point of view they are all just one and same device. Number of slots in expander unit is not limited and their numbering is made only for humans. You can plug all extensions to any slot and it does not make any difference. (More similar to MSX I/O slots) In the special case of RAM cartridge you can use dip switches to select what memory banks it should attach to. (21/22/31/32) In theory these memory bank pins could be used to implement extension in MSX style, but in real life it would be quite useless as there is no software support in ROM to handle such situation.

Fault of this design was that extensions in expander unit could not include software -> No disk ROM -> They ended up with this kind of weird disk format. -> They made the design a bit better on MSX... yet long way from perfect.

By eimaster

Expert (67)

eimaster's picture

07-11-2016, 18:44

Where can i find DSK2DMK?

By eimaster

Expert (67)

eimaster's picture

07-11-2016, 19:00

I had my first MSX1 nearly at the same time i had my SVI-328.To me both systems are jyst like twins but one of them is crippled and has some kind of DNA deseases (SVI) and the other is fully healthy (MSX). I think that MSX is a successful redesigned, rebuild & reproduction of the SVI-3x8 system. Especially that both of them nearly have the same CPU, video, audio abilities.
Although I said that SVI is a crippled version of MSX but I still love it just as much as I love MSX. After all, both twins were the reason I got attached to computer world and computer programming world. Thanks to them both. In fact, I will be very happy to be able to run SVI-3x8 on my Android mobile 'cos I can't use my PC due to no electricity as a result of US-Saudi aggression on my country Yemen.
What do you think of that?!

By Manuel

Ascended (12816)

Manuel's picture

07-11-2016, 22:55

The hacked DSK2DMK is not available, but the original is only available in source code at the moment, in the openMSX repository. See https://github.com/openMSX/openMSX/tree/master/Contrib/dmk

By eimaster

Expert (67)

eimaster's picture

07-12-2016, 00:51

Have you visited Roger's Spectravideo page?! It contains lots of valuable information about SV "Spectravideo" and SVI "Spectravideo International" computers.

By NYYRIKKI

Enlighted (4426)

NYYRIKKI's picture

07-12-2016, 14:11

eimaster wrote:

Have you visited Roger's Spectravideo page?! It contains lots of valuable information about SV "Spectravideo" and SVI "Spectravideo International" computers.

Indeed it contains lot of valuable information, but also lot of inaccurate and even false information. Roger is not currently correcting any errors pointed to him, therefore I can't really recommend the page without fair warnings. Viewer discretion advised.

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