OLPC hardware: what if there was an SDR modem / chipset?

Benjamin M. Schwartz bmschwar at fas.harvard.edu
Tue Jan 26 09:47:45 EST 2010

Luke Kenneth Casson Leighton wrote:
>  if i want to write my own
> peer-to-peer 802.11 algorithms, doing an implementation e.g. of the
> Babel routing algorithm to run actually on the WIFI chip itself, can i
> do so, right now, _without_ being forced to sign a Marvell NDA?

The 88W8686 in the XO-1.5 is basically a dumb interface.  There isn't
really a WIFI "chip" that can run anything.  This means that yes, you
_can_ implement Babel as a first-class mesh implementation on the XO-1.5,
just by running it on the CPU.  This is unlike the XO-1, which used the
88W8388's built-in ARM core to handle mesh routing without waking up the CPU.

The ostensible disadvantage of mesh routing on the CPU (which, btw, was
tried with Cerebro on the XO-1) is that it prevents the CPU from sleeping
to save power.  According to the OLPC product plan, the next laptop is
supposed to be the XO-1.75, with an ARM CPU.  Given ARM's ability to do
fast suspend+resume, it's possible that running short tasks on the main
CPU (like forwarding one packet) would be just as efficient as running
them on some coprocessor.

So don't be discouraged from pursuing interesting routing algorithms.
Also, consider implementing them with the kernel's 802.11s stack.  802.11s
allows basically any routing algorithm as long as all nodes agree.


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