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Re: Using external DMA in output direction

----- Original Message -----
From: "Arne Bockholdt" <abockholdt@xxxxxxx.de>
To: <dev-etrax@xxxxxxx.com>
Sent: den 3 mars 2003 17:34
Subject: Using external DMA in output direction

> Hi,
> we try to use the external DMA in output direction and we've run in some
> problems :
> * DMA channel 4 is allocated by "cascade" whatever that means on a CRIS
> system, so it seems that this external dma channel is useless for DMA in
> output direction, because the output channel isn't available.
> * DMA channel 6 seems to be used by serial p0 port. This is the output
> channel for ext_dma1. We don't want to change the debug/rescue etc port to
> another port than p0, so it seems that external DMA channel 1 is useless
> too.
> Questions:
> * Is there any possibility to use ext_dma0 in output direct (internal
> channel 4), disabling the "cascade" allocation ?

Looks like a bug (to PC specific) in kernel/dma.c in the dma_chan_busy
There should probably be within some #ifdef around that and a {0, 0 }, entry
In our elinux (2.0) we have an #ifndef __CRIS__ there, must have been
in the port...

> * Is there any possibility to disable the usage of DMA for serial p0 so
> that ext_dma1 can be used ?

Currently not without disabling the entire serial port. It's on a TODO
list to add support for non-DMA serial input and output.
Can't promise any delivery time though...

> * Is there any other possibility to use ext_dma in output direction ?

Can't think of any, but the cascade fix is simple.

> Thanks in advance,
> Arne Bockholdt
> Dipl. Inform. Arne Bockholdt
> REA Elektronik GmbH
> Teichwiesenstr. 1
> 64367 Mühltal-Waschenbach
> Tel. +49 (0) 6154 / 638-115, Fax -195
> ABockholdt@xxxxxxx.de

Best regards
Johan Adolfsson, Senior Software Engineer
Embedded Platform Team
Axis Communications AB    E-mail: Johan.Adolfsson@xxxxxxx.com
Phone: +46-(0)46-272 1906, Fax: +46-(0)46-136130 http://developer.axis.com/