[U-Boot] at91 spi bus speed

[U-Boot] at91 spi bus speed

[wouter moors]

Hi,

I'm experiencing some strange spi behaviour with an at91sam9g20.
I changed the spi_xfer code (atmel_spi.c) to make use of the PDC that the
at91sam9g20 offers. This works fine, but only up to an spi bus speed of 10
to 12 MHz. After that I see the CS going down sometimes before the transfer
is complete. When the frequency is increased the issue starts appearing more
often.

I saw that in env_sf.c that the spi bus speed is set at 10 MHz and was
wondering if there was a specific reason for that?

10 MHz is acceptible but I would like to understand what is happening, so if
anybody experienced and maybe even investigated the problem, please let me
know.

Wouter Moors

-- 
there's only 10 kinds of people. The ones that understand binary and the
ones that don't.

[U-Boot] at91 spi bus speed

[Mike Frysinger]

On Tuesday, February 15, 2011 06:56:42 wouter moors wrote:
> I saw that in env_sf.c that the spi bus speed is set at 10 MHz and was
> wondering if there was a specific reason for that?

you mean it defaults to 10 MHz.  boards can freely pick anything they want.  
some speed needed to be arbitrarily picked, and 10 MHz should work with every 
spi flash out there.
-mike
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[U-Boot] at91 spi bus speed

[wouter moors]

So the 10MHz is a safe value I guess.
But I was wondering most why the bus speed seems to be limited to ~12MHz. Is
that a limitation of the at91sam9g20 or more likely a problem with the board
design?



On Tue, Feb 15, 2011 at 9:08 PM, Mike Frysinger <vapier@gentoo.org> wrote:

> On Tuesday, February 15, 2011 06:56:42 wouter moors wrote:
> > I saw that in env_sf.c that the spi bus speed is set at 10 MHz and was
> > wondering if there was a specific reason for that?
>
> you mean it defaults to 10 MHz.  boards can freely pick anything they want.
> some speed needed to be arbitrarily picked, and 10 MHz should work with
> every
> spi flash out there.
> -mike
>



-- 
there's only 10 kinds of people. The ones that understand binary and the
ones that don't.

[U-Boot] at91 spi bus speed

[Mike Frysinger]

On Wednesday, February 16, 2011 03:26:00 wouter moors wrote:

please dont top post

> But I was wondering most why the bus speed seems to be limited to ~12MHz.
> Is that a limitation of the at91sam9g20 or more likely a problem with the
> board design?

i was merely covering a question on common code.  ive never used u-boot on an 
arm part let alone the one you quote, so i dont have a clue in that regard.  
sorry.
-mike
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