[U-Boot-Users] Re: Burst I/O on PPC440GP

[Gregg Nemas <gnemas@gmail.com>]

Stefan Roese <sr <at> denx.de> writes:

> > I've been testing this by using the u-boot mw.l command. Do I need to use
> > PPC-specific instructions to perform burst I/O, or should an ordinary
> > programmed I/O (using 32-bit write operations) be automatically queued up
> > and converted to burst transactions?
> 
> Do you want to transfer bigger chunks of data? If yes, you may want to take a 
> look at the dma controller of the 440gp. It definately is able to generate 
> burst transactions and probably the ideal solution for your needs.

No, actually it will be relatively small transfers (16-128 bytes). I considered
using the DMA controller, but thought I would start out simple.

> Another way to get burst transactions, is of course to use the cache, but I 
> don't think that this is what you are looking for.

You say "of course", but it really isn't at all clear to me how this works. Why
does enabling the cache allow burst operations? You are right that it is not
what I would normally want to do for device I/O memory.

Thanks for your help.

Gregg