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From: Peter Maydell <peter.maydell@linaro.org>
Date: Sun, 2 Jul 2017 22:00:40 +0100
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Subject: Re: [Qemu-devel] [Qemu devel v5 PATCH 0/5] Add support for
 Smartfusion2 SoC
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To: sundeep subbaraya <sundeep.lkml@gmail.com>
Cc: =?UTF-8?Q?Philippe_Mathieu=2DDaud=C3=A9?= <f4bug@amsat.org>, QEMU Developers <qemu-devel@nongnu.org>, qemu-arm <qemu-arm@nongnu.org>, Peter Crosthwaite <crosthwaite.peter@gmail.com>, Alistair Francis <alistair23@gmail.com>

On 2 July 2017 at 18:39, sundeep subbaraya <sundeep.lkml@gmail.com> wrote:
> I figured out that systick uses cpu clock as clock source and
> system_clock_scale
> need to be set in msf2-soc.c. There is a bug in u-boot where it uses cpu
> clock as
> systick input but configures systick in external clock mode. I have tested
> the modified
> u-boot on real hardware too and it works fine. I am calculating
> system_clock_scale
> as below:
> If CPU clock is X MHz then system_clock_scale = (1 / X) * 1000
>
> Tested with different frequencies and they are yielding same results.

If you calculate it like that you'll probably get rounding
errors. Better is
  system_clock_scale = NANOSECONDS_PER_SECOND / freq_in_hz;

(Our systick implementation hardwires the external clock
frequency at 1MHz, but this is not really correct, it
depends on the SoC.)

thanks
-- PMM