Subject: Re: MPC8308 bursting question

From: David Hawkins <[email-masked]>
Date: Fri, 27 May 2011 07:26:37 -0700

Hi Bruce,

> This isn't really a Linux PPC question, but this is the smartest mailing
> list I know for asking PPC hardware questions, so here goes.
>
> We're using an MPC8308 and want to use the DMA engine to move data in and
> out of an FPGA hanging on the local bus.  Our bandwidth/local bus burden
> calculations were done assuming that we could use bursting.  So I've setup
> a UPM to do single beat and burst reads/writes.  I've also configured my
> DMA TCD to use a data transfer size of 32-bytes when accessing the FPGA.
> The problem I'm having is I can't seem to get the UPM to ever trigger the
> burst write sequence using the DMA.  Single beat reads and writes work
> okay, but no bursting.  In fact, the only thing I've been able to find in
> the manual that causes a burst transaction is a cache line miss, which is
> wholly in the purview of the core and really does me no good.
>
> Does anyone know of any way (short of issuing a run command to the UPM via
> MxMR) to force a burst transaction on the 8308?  Am I just being dumb and
> missing something totally fundamental?

Read my MPC8349EA UPM setup notes and see if you have used
similar settings (I assume the local bus UPMs are similar):

http://www.ovro.caltech.edu/~dwh/carma_board/carma_sys.pdf

Do you have a Modelsim simulation of your interface?
I have a VHDL bus-functional-model I wrote that I can
send you.

Cheers,
Dave