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Date: Mon, 18 Feb 2008 11:57:56 -0800 From: David Brownell <david-b@...bell.net> To: spi-devel-general@...ts.sourceforge.net Cc: Atsushi Nemoto <anemo@....ocn.ne.jp>, hskinnemoen@...el.com, linux-kernel@...r.kernel.org Subject: Re: [spi-devel-general] atmel_spi clock polarity On Monday 18 February 2008, Atsushi Nemoto wrote: > IIRC the clock state follows > CSRn.CPOL just before the real transfer. No ... clock state should be valid *before* chipselect goes active. So I'm thinking the patch from Haavard is likely the right change. > Like this (previous transfer > was MODE 0, new transfer is MODE 3): > > T0 T1 T2 > > CS ~~~|________________________________________________ So at T0, some chip is selected (and never deselected) ... > > CLK ______________________|~|___|~~~|___|~~~|___|~~~|___ ... and at T1 CPOL is changed?? That's wrong. There should never be a partial clock period while a chipselect is active. While it's inactive, sure -- no chip should care. > > SO ~~~~~~~~~~~~~~~~~~~~~~~~~~|___|~~~|___|~~~|___|~~~|_ > MSB > > T0-T1 was relatively longer then T1-T2. I suppose T1 is not the > point of updating MR register, but the point of starting DMA transfer. > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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