[ECOS] Re: ecos realtek driver

[Eric Doenges <Eric dot Doenges at DynaPel dot de>]

Andy Dyer wrote:
> I saw your message about cache coherency, and I think
> you're right that a cache flush needs to happen after 
> the transmit copy to buffers.
>
> I'm not so certain about the receive cases - at least
> on mips the HAL_DCACHE_SYNC is going to write lines
> out to memory trashing the stuff your net controller
> just put in there.  I think for receive it should be
> HAL_DCACHE_INVALIDATE, but you would have to make sure
> that no non-buffer data gets affected by that.

My assumption is that for the receive case, there is no reason for
the data cache to contain dirty cache lines, since the driver should
only ever read from that portion of memory. Of course, that means
a HAL_DCACHE_INVALIDATE is all that is really needed. But that
opens a new can of worms - how to determine which cache lines need
to be invalidated, and how to make sure that the buffers allocated
start and end on cache line boundaries to prevent interfering with
other memory areas. While this shouldn't be too much of a problem
for any given platform, doing this in a generic, portable way most
certainly is.


P.S.: I've CCed this mail to ecos-discuss in the hope someone more
knowledgeable than me has some good ideas on cache coherency in eCos.
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