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From: David Brownell <david-b@pacbell.net>
To: spi-devel-general@lists.sourceforge.net
Cc: Atsushi Nemoto <anemo@mba.ocn.ne.jp>,
	hskinnemoen@atmel.com, linux-kernel@vger.kernel.org
Subject: Re: [spi-devel-general] atmel_spi clock polarity
Date: Mon, 18 Feb 2008 11:57:56 -0800	[thread overview]
Message-ID: <200802181157.57299.david-b@pacbell.net> (raw)
In-Reply-To: <20080218.231243.41197917.anemo@mba.ocn.ne.jp>

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.
> 

  parent reply	other threads:[~2008-02-18 20:16 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2008-02-16 13:32 Atsushi Nemoto
2008-02-18 11:42 ` Haavard Skinnemoen
2008-02-18 14:12   ` Atsushi Nemoto
2008-02-18 14:31     ` Haavard Skinnemoen
2008-02-20  5:21       ` Atsushi Nemoto
2008-02-20  9:34         ` Haavard Skinnemoen
2008-02-20  9:50           ` Atsushi Nemoto
2008-02-21  1:33             ` David Brownell
2008-02-21  1:32           ` David Brownell
2008-02-18 19:57     ` David Brownell [this message]
2008-02-18 22:49       ` [spi-devel-general] " Haavard Skinnemoen
2008-02-19 14:51         ` Atsushi Nemoto

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