[gta02-core] ECN0001 comments+patch on SPI
werner at openmoko.org
Mon Sep 7 21:47:25 CEST 2009
Rask Ingemann Lambertsen wrote:
> Figure 22-2 of the SC32442B manual shows SPI data changing on SPI clock
Yeah, I wouldn't be at all surprised if the "disabled" accelerometer
misfired every once in a while. This kind of design is practically
begging for it ...
> The direction of shift doesn't matter so much if you send software SPI
> clock pulses, just ask the card for e.g. firmware revision and discard bits
> until the alignment is right.
Hmm, I'm not entirely sure, but I think the game starts again for
each SDIO transfer.
Our main user of fast SPI would be WLAN, which we'll never see in
this form again after gta02-core anyway. So I wouldn't put much
effort into debugging 2442 SPI, considering that a real product
would use a different CPU anyway.
E.g., even if we want to stay very close to the gta02-core design,
the 2450 would be a much nicer choice than the 2442:
> The thing is that the 2442 SPI interface is poorly documented in places.
Indeed. Quite a lot about the 2442 looks a bit like a rush job.
> Does it mean that gta02-core WLAN SPI is effectively limited to
> 66 MHz / 3 = 22 MHz rather than 66 MHz / 2 = 33 MHz?
Good point. I guess we just have to try and see what happens :-)
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