OCM: questions and answers

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By cax

Prophet (3721)

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06-12-2006, 19:04

Now, when OCM's VHDL code is available on the net (and some lucky people already started playing with the device), some questions about it already can be answered by just studying the code.

Here is what I've discovered from the code
(see Grauw's blog for downloading OCM CD: http://www.grauw.nl/blog/entry/385 )

1) USB is not implemented at all

2) working speeds:
-- 3.58MHz (standard speed)
-- 10.74MHz (workaround for boot failure)
(commented out) -- 21.48MHz (much troublesome with external device)

Please post your discoveries (like Grauw's note about RTC that is not saved on power off) !

Some open questions that I'd like to be answered:

1) The code was compiled using Altera's Quartus II
Version 6.0 Build 202 06/20/2006 Service Pack 1 SJ Web Edition

Can we use the free web edition 6.1 instead (downloadable from Altera's site) ?

2) Will changing CPU speed change also VDP speed ?

3) There are some small tools on OCM CD with docs in Japanese.
In short, what are they all for ?

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By msd

Paragon (1372)

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06-12-2006, 19:18


(commented out) -- 21.48MHz (much troublesome with external device)

This could be a usefull speed with the gfx9000 and opl4.. They can handle higher bus speeds Smile

By Leo

Paragon (1236)

Leo's picture

06-12-2006, 19:42

Great !!! thanks for the vhdl code !!!!

By dvik

Prophet (2200)

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06-12-2006, 19:56

Leo, where did you get the vhdl code?

By cax

Prophet (3721)

cax's picture

06-12-2006, 20:05

dvik, in Grauw's blog, as I said above.

By dvik

Prophet (2200)

dvik's picture

06-12-2006, 20:51

ah sorry, I missed that. I'll also download it and take a look.

By Prodatron

Paragon (1788)

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06-12-2006, 21:38

1) USB is not implemented at all

Does someone know, if the OCM is USB master or would just act as a slave device? (if someone will implement USB at all)

2) Will changing CPU speed change also VDP speed ?

Very interesting question, as it would increase the speed in several software a LOT. But someone posted, that the VDP already works with 21Mhz, even if the Z80 runs in 3,5MHz mode. What does it mean?

By dvik

Prophet (2200)

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06-12-2006, 22:29

Is there any persistent memory in the OCM, e.g. sram?

By AuroraMSX

Paragon (1900)

AuroraMSX's picture

07-12-2006, 13:12

Is there any persistent memory in the OCM, e.g. sram?Isn't it possible to configure a part of the FPGA as SRAM?

By cax

Prophet (3721)

cax's picture

07-12-2006, 13:54

So, anybody tried to compile the VHDL code himself ?

By Grauw

Enlighted (7960)

Grauw's picture

07-12-2006, 14:22

1) USB is not implemented at all
That was known in advance Smile.

1) The code was compiled using Altera's Quartus II
Version 6.0 Build 202 06/20/2006 Service Pack 1 SJ Web Edition

The 6.0 web edition is included on the CD.

Isn't it possible to configure a part of the FPGA as SRAM?
Maybe, but I don’t think so.

(commented out) -- 21.48MHz (much troublesome with external device)
Interesting, that makes sense.

2) Will changing CPU speed change also VDP speed ?
I don’t think so, but I haven’t tested. Someone on my blog asked whether I could measure command execution speeds, I suppose I’ll have to do that.

~Grauw

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