[Tinyos-devel] Copying directly from RxFIFO to TxFIFO of CC2420

[Adam Dunkels]

Razvan Musaloiu-E. wrote:
> On Thu, 14 Aug 2008, Sagar Bijwe wrote:
>> I should have elaborated more. I just needed to know whether there exists a
>> control command (i could not find in CC2420 datasheet)  to transfer data
>> directly from rxbuffer to txbuffer. I don't want to use any external kit for
>> the purpose of programming CC2420. Driver level modifications can be handled
>> once i know that such a command exists. According to current implemenation,
>> we have to first copy pkt from rxbuffer to msp & then to txbuffer (this
>> makes spi bus bottleneck). I want to remove this critical path. Thanks for
>> your response anyway.

It is not possible to copy data from the rxbuffer to the txbuffer on the 
CC2420, nor is it possible to transmit from the rxbuffer, but it is 
possible to remove copying from the critical path:

> If this is what you want to do then you'll probably find relevant this 
> paper:
>  	http://www.sics.se/~adam/osterlind08approaching.pdf

In the above paper, we achieve a very high multi-hop throughput (109 
kbit/s over a 250 kbit/s radio, 97% of the theoretical max) by moving 
the copying away from the critical path. We provide an abstraction that 
allows an upper layer protocol to immediate transmit a packet when an 
incoming packet arrives. The upper layer protocol decides to transmit or 
not after inspecting just a few bytes in the header of the incoming 
packet and does not need to read the entire packet from the radio 
controller. Packet copying and all the normal stack processing is done 
afterwards, away from the critical path.

The price for the higher throughput is an increased per-hop latency.

/adam
-- 
Adam Dunkels <adam at sics.se>
http://www.sics.se/~adam/