Scatter Gather DMA

Scatter Gather DMA

[mjander]

Hi,

Another question... :)

The Aureal Vortex has Scatter Gather DMA's for each audio channel.
But these SG DMA
support only max 4 pages. Each page can have a programable size of
upto 4 KB.
I was studying the ALSA SG scheme and it doesnt seme to fit into
the aureal vortex
SG buffer scheme, because ALSA, as far as i understood, only
allows pages of the kernel PAGE_SIZE size, and allocates as many
pages (without cound limit ?) until the buffer size is  reached.
But the PAGE_SIZE around 0x400 or 0x800, which is rather small.

On the Aureal vortex soundcard side i have 4 registers for page
base address, and some sort  of config regs to configure each page
size and the next page for each page. I just dont understand how
could i plug this two apparently incompatible things together.

Thank you very much.

Manuel Jander.
.
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Re: Scatter Gather DMA

[Jaroslav Kysela]

On Wed, 5 Mar 2003, mjander wrote:

> Hi,
> 
> Another question... :)
> 
> The Aureal Vortex has Scatter Gather DMA's for each audio channel.
> But these SG DMA
> support only max 4 pages. Each page can have a programable size of
> upto 4 KB.
> I was studying the ALSA SG scheme and it doesnt seme to fit into
> the aureal vortex
> SG buffer scheme, because ALSA, as far as i understood, only
> allows pages of the kernel PAGE_SIZE size, and allocates as many
> pages (without cound limit ?) until the buffer size is  reached.
> But the PAGE_SIZE around 0x400 or 0x800, which is rather small.
> 
> On the Aureal vortex soundcard side i have 4 registers for page
> base address, and some sort  of config regs to configure each page
> size and the next page for each page. I just dont understand how
> could i plug this two apparently incompatible things together.
> 
> Thank you very much.

I don't see a problem here. The PAGE_SIZE is 4kB for i386. Simply
follow the code in the via82xx driver and limit the maximum count of 
periods to 4.

						Jaroslav

-----
Jaroslav Kysela <perex@suse.cz>
Linux Kernel Sound Maintainer
ALSA Project, SuSE Labs



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Re: Scatter Gather DMA

[tomasz motylewski]

> I don't see a problem here. The PAGE_SIZE is 4kB for i386. Simply
> follow the code in the via82xx driver and limit the maximum count of 
> periods to 4.

This is easy solution, but a bit limiting. For example cs4281 supports max 2
periods. It is rather hard to work with it. There is a patch for ALSA 0.5 (by
Pekka Pessi) which I have ported to 0.9 which is switching DMA addresses in the
end-of-period interrupt. Works nicely, unlimited number of periods. Similar
solution could be used here. Or do you expect problems with it? 

Best regards,
--
Tomasz Motylewski



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Re: Scatter Gather DMA

[Takashi Iwai]

At Wed,  5 Mar 2003 12:09:21 -0400,
mjander wrote:
> 
> Hi,
> 
> Another question... :)
> 
> The Aureal Vortex has Scatter Gather DMA's for each audio channel.
> But these SG DMA
> support only max 4 pages. Each page can have a programable size of
> upto 4 KB.
> I was studying the ALSA SG scheme and it doesnt seme to fit into
> the aureal vortex
> SG buffer scheme, because ALSA, as far as i understood, only
> allows pages of the kernel PAGE_SIZE size, and allocates as many
> pages (without cound limit ?) until the buffer size is  reached.

then you can define max_buffer_bytes as 4 * 4096.
then sg-allocator will allocate up to 4 pages.

> But the PAGE_SIZE around 0x400 or 0x800, which is rather small.

sorry, what are these numbers?

> On the Aureal vortex soundcard side i have 4 registers for page
> base address, and some sort  of config regs to configure each page
> size and the next page for each page. I just dont understand how
> could i plug this two apparently incompatible things together.


Takashi


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