[Coco] Device module for (O)VCC continues. How to do DMA?

[Walter Zambotti]

Thanks Gene.

You're supposed to break it to me GENTLY!

So it simply isn't possible to design a hardware pak with DMA regardless of whether it is to the 64k or the 512k memory map!

I suppose the DMA PAC feature in VCC (& OVCC) is an extension to the CoCo design.

Walter

-----Original Message-----
From: Coco [mailto:coco-bounces at maltedmedia.com] On Behalf Of Gene Heskett
Sent: Sunday, 2 June 2019 3:30 PM
To: coco at maltedmedia.com
Subject: Re: [Coco] Device module for (O)VCC continues. How to do DMA?

On Sunday 02 June 2019 12:17:24 am Walter wrote:

> Ok
>
>
>
> So I have my MPU pak module (PFU & GPU) successfully performing 
> floating point operations and drawing under OS9.
>
>
>
> However it only works in synchronous mode.  In async mode it corrupts 
> task memory and after several hours of debugging I now know why but 
> I'm unsure how to fix the issue.
>
>
>
> The problem turns out to be the GPU can only DMA into the same 64k 
> address that the process is running in.
>
>
>
> If OS9 switches the MMU memory map the GPU is completely unaware and 
> continues drawing into wrong memory.
>
>
>
> The GPU has no way of knowing the MMU has pulled the memory rug from 
> under its feet!
>
>
>
> So my question is:
>
>
>
> How does a physical pak device accomplish DMA given this limitation?
>
>
>
> Can a PAK device see (and DMA) into the full (512k/1M/2M) ?
>
No. There is no "dma" anyplace in the coco's design.
>
> If yes, how?
>
>
>
> If no, what is the work around?
>
>
>
> Walter


Cheers, Gene Heskett
--
"There are four boxes to be used in defense of liberty:
 soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
Genes Web page <http://geneslinuxbox.net:6309/gene>


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