Uncovering the R800

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By MSX-ALL

Supporter (12)

MSX-ALL's picture

16-11-2019, 20:37

I am just curious... Wasn't this manual (R800UsersManual.zip) already published at File Hunter (https://download.file-hunter.com/Books/EN/) for quite a while?

Don't take me wrong, I understand the importance of the documentation. I simply don't understand how it is "news". :)

Other than that, what would be the real impact for the current emulators (that offer R800) and for the MSX itself as a "community-maintained standard" in terms of what else can be done with the MSX Turbo-R based on those new discoveries?

Besides, in the list of new hardware released in the last few years, is there any new homebrew computer that claims to be compatible with MSX Turbo-R? If so, any impact on those?

Thanks. @msxall

By Meits

Scribe (5647)

Meits's picture

16-11-2019, 21:41

They're the same files. The files in the archive on file-hunter are of 15-11-2019 (today that's yesterday, the day juangotoh posted it). Unless tfh says otherwise, I think it's a copy of juangotoh's.

By MSX-ALL

Supporter (12)

MSX-ALL's picture

16-11-2019, 21:27

Ok. My bad then... Smile

What about the other considerations in the question about the impact and possibilities?

By tfh

Paragon (1842)

tfh's picture

16-11-2019, 21:40

Meits wrote:

They're the same files. The files in the archive on file-hunder are of 15-11-2019 (today that's yesterday, the day juangotoh posted it). Unless tfh says otherwise, I think it's a copy of juangotoh's.

I will not say otherwise Hannibal
Just trying to keep that archive as complete as possible.

By Edevaldo

Master (134)

Edevaldo's picture

16-11-2019, 21:50

For emulators it will allow a more accurate memory timing emulation, or at least confirm the accuracy of the current implementation.

For the machines, some have added 1Mb-4Mb to the machines already. It is a much bigger hack than enabling the features we now have documentation for. I can easily see a Turbo-R with 8Mb of RAM and the DMAs/Ints hooked up.

On the other hand, none of those features are really part of the CPU core itself. They are just peripherals. It is not too difficult to add those around a regular Z80 if one feels so inclined.

By l_oliveira

Hero (529)

l_oliveira's picture

17-11-2019, 19:12

They disabled this stuff because this was intended to help putting data faster into the VRAM of the new VDP which never came to be.

Having the mapper controller (MMU) and DMA inside the CPU would allow these two to interact with each other. Having these units active only made sense if they could be used to automate pushing data into the VDP and since the new VDP never got ready in time, they killed the new features and set it up in a way it could still be used for the speed gains (hence the name Turbo, I suppose.)

Having these features active would require development of software support on the system ROMs, testing against older software and documenting the system changes. They scrapped everything as they were mostly trying to salvage the costs of developing what was already done. They put a new MMU into the system engine (S1990) and the MMU+DMA inside the R800 went unused.

Oh well.

By ducasp

Master (163)

ducasp's picture

17-11-2019, 23:06

But DMA could have potential good uses, like faster disk interfaces that didn't depend on the CPU as much, scanners and other stuff... It is too bad that Turbo-R ended up as this half baked effort, it could have been so much more, but I always thinks that MSX was always lagging a generation behind trying to save a few dollars, 2+ is what 2 should have been, and Turbo-R should have been 2+...

By erpirao

Paladin (962)

erpirao's picture

17-11-2019, 23:46

ducasp wrote:

But DMA could have potential good uses, like faster disk interfaces that didn't depend on the CPU as much, scanners and other stuff... It is too bad that Turbo-R ended up as this half baked effort, it could have been so much more, but I always thinks that MSX was always lagging a generation behind trying to save a few dollars, 2+ is what 2 should have been, and Turbo-R should have been 2+...

For the truth, if the turboR had been the msx2 +, that is, the R800 in 1988, would have been amazing, and even with the slow VDP it would be a much more competing machine.

By Edevaldo

Master (134)

Edevaldo's picture

18-11-2019, 00:42

Performance wise the R800 performs close to the 68k in early Macs and Amigas. It would have been very "competitive", maybe until middle to late eighties. Just talking raw performance. But we need to keep in mind that the 68K was a 10 year old design by 1987. 386s and 68030's were ruling the world already and risc designs were popping everywhere.

The MSX as a whole was always thought to undercut price in the already competitive market of home computers (even in 1983). By that time the Z80 was almost a decade old already. 5 years latter it was already more than 50 times slower than a high end PC ($$$$$).

Maybe the R800 was conceived in 86-87 era and it looked good at the time. But the vision was not updated as it moved forward.

The DMA in the R800 is very flexible it could be used for video, memory copies, disk IO, etc. I do not believe it was there just for video. No need to have two of it if this was the case. And also the memory mapping and interrupts do not help video as much.

The amount of circuitry needed to enable the new features and use the DMA for disk transfers, for example, is pretty small.

But I hopped that the R800 had a magic way of entering in a 16bit mode that would give it a better way to access memory, even if it was the segmented manner of the 8086. Maybe allow PC, DATA and Stack to be fetched from different 64k windows like the 65816 (6502).

By gdx

Prophet (3083)

gdx's picture

18-11-2019, 15:36

ducasp wrote:

I always thinks that MSX was always lagging a generation behind trying to save a few dollars, 2+ is what 2 should have been, and Turbo-R should have been 2+...

I don't think the problem is this.
MSXs did not make any good enough significant upgrade from one generation to another because the next one was too much based on the previous one. The R800 is largely under exploited because of that. It is very constrained by the old architecture.
I think it could have been cheaper and beneficial by creating something separate for each new generation.

A simple system of turbo as I speak in the talking wire and a stereo sound for the MSX2 would have been fantastic without hight costs.
https://www.msx.org/forum/msx-talk/general-discussion/what-i...

The problem of MSX2+ must have been caused by the defection of Microsoft. ASCII had to struggle to stay on course.

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