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From: Atsushi Nemoto <>
Subject: Re: [spi-devel-general] atmel_spi clock polarity
Date: Tue, 19 Feb 2008 23:51:23 +0900 (JST)	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <20080218234918.3d09022a@siona>

On Mon, 18 Feb 2008 23:49:18 +0100, Haavard Skinnemoen <> wrote:
> > > 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.
> ...but what I'm afraid of is that since we're using GPIO chipselects,
> the controller may _think_ that no chip is selected and change the
> clock polarity just before it would pull the chipselect low if we were
> using automatic chipselects...

Yes.  That's I suppose.

> If that's the case, it would be a bit strange if it actually helped to
> initialize all the CSRn registers, but it would also offer us a nice
> workaround...

I suppose the clock state of the AT91 just follows _last_ transfer.
My patch (setting all CSRn.POL for next transfer) was based on that

> Atsushi, do you by any chance have debugging enabled? That would
> explain the long delay from CS activation to the change of clock
> polarity. Compared to printk() the DMA setup takes almost no time at
> all.

No, I did not enabled debugging.

> If you can confirm that my patch helps, I think that's the one we want
> in mainline.

Unfortunately I had no time to try it today.  Hopefully tomorrow...

Atsushi Nemoto

      reply	other threads:[~2008-02-19 14:51 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     ` [spi-devel-general] " David Brownell
2008-02-18 22:49       ` Haavard Skinnemoen
2008-02-19 14:51         ` Atsushi Nemoto [this message]

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