[net2-wg] 600 pps, high throughput

[henri dubois-ferriere]

Jonathan, do you have a working SPI over DMA  implementation under 2.x
and if so are you planning to commit it?

I'd be very interested to use it on tinynode: not so much to increase
throughput as with the cc2420, but simply to stay within the very
tight timing constraints to run the xe1205 radio at high bitrates.

thanks
henri

On 14/03/06, Jonathan Hui <jwhui at cs.berkeley.edu> wrote:
> On 3/13/06, Philip Levis <pal at cs.stanford.edu> wrote:
> > As Joe's pointed out in the past, the best solution is to use DMA
> > (assuming you have a free DMA channel). If you have CSMA enabled, none
> > of this makes a big difference, though, as the CSMA latency is greater
> > than the loading time. I think Jonathan was planning on checking in a
> > DMA version at some point, based on the re-architecture of the MSP430
> > USART system Vlado, he, and I came up with after the TTX. He's been
> > doing some pretty serious performance tradeoff comparisons, so probably
> > has some good thoughts on the matter.
> >
> > Jonathan?
>
> The tradeoffs are pretty obvious. As Phil pointed out, the expected
> backoff time can far exceed any lost time by not using the DMA
> controller. Utilizing DMA would actually be more useful to pull
> packets out of the radio, but contention under CSMA often keeps
> packets from coming in back to back. If backoffs are turned off,
> utilizing DMA would definitely have a greater impact on overall packet
> throughput (both transmitting and receiving).
>
> One issue is that the msp430 only provides three DMA channels, two of
> which would be required for full DMA support on the SPI. While, the
> DMA can be helpful for packet training optimizations it also limits
> their use for other potentially crucial tasks as sampling the ADC.
>
> --
> Jonathan W. Hui
> jwhui at cs.berkeley.edu
> http://www.cs.berkeley.edu/~jwhui/
>