Re: [video] VGA controller implementation

[Richard Herveille <richard@asics.ws>]

> On Tue, 2002-07-09 at 15:34, Richard Herveille wrote:
> > That's true of course. But I figured it would be a first step to a decend
> > open-source video system. There are a few around, and I subscribed to
> > many of the mailing lists. But just like this list they are kinda dead.
>
> Yes that would be nice.. make a open-source video system that has
> capabilities to be used for more functions.. maybe we can work with the
> bunch of people working on a 3D accelerator too..

Wouldn't that be cool?
>
> > I also want to provide a port for direct video access. This would allow
> > an outside source (a mpeg decoder for example) to display data. All the
> > video stuff would be handled by the vga card, the outside-source just has
> > to provide the data.
>
> This would be really cool.. I think that you can already do this..
> depending on how things are designed.. because your VGA accesses it's
> video RAM from an external source, all that's needed is a block to do
> the translations (assuming an external digital source).. The fact that
> it accesses external VideoRAM makes it easy to read data from an outside

Ah that's how you want to do it. Yes it can be done like that, but then you 
need an additional piece of memory. Hmm maybe not such a bad idea after all, 
that would also take care of corrupted images caused by differences in 
refresh-rates. Interresting.

>
> source.. we just need to masquerade it.. (:
> > The vga card doesn't set the data-lines to zero, it presents the next
> > pixel's data. The blank signal blanks the screen. There's an intensity
> > difference between black and blank (black is less black than blank).
>
> Ah.. So how do we get the core to send a BLACK when it reaches beyond
> the 640 width?? the easiest way is to cheat and make the picture graphic
> with a 1pixel black border.. hehe.. (: is there a hardware way without
> modifying the core too much??

It's not that hard (if I am not mistaken pretty easy actually). But you have 
to wait a few weeks. I am moving (to another country) and my file server went 
ahead (Fed-Ex-ed it). I am moving in two weeks.

>
> > For FPGAs I always use the VENDOR_FPGA setting. I use Leonardo Spectrum
> > and Synplicity as synthesizers/compilers. They both
> > 'understand/recognize' the structure described and generate RAM blocks
> > for it.
>
> Ah yes.. I guessed as much.. most people use Synplicity.. I'm using FC2
> because I have access only to FC2.. it's given free with the other
> Synopsys products, I think.. it's not smart enough to automagically
> recognize the RAM..

FPGA-Compiler2 huh, and it doesn't understand the RAM thingie huh.
I already knew that FPGA-Express doesn't recognize it (worst piece of FPGA 
tool I've had to work with). But the fact that FC2 doesn't recognize it is 
straight out sad. You would expect Synopsis to do better than that.

Richard

>
> with metta,
> Shawn Tan.

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