[meta-xilinx] Zynq TTC usage by Linux

[Edward Wingate]

On Sat, Oct 22, 2016 at 3:06 AM, Mike Looijmans <mike.looijmans at topic.nl> wrote:
> One of the TTCs used to be used for clock source. This should still be the
> case if you use dynamic clocks, because the ARM timer is fixed to the CPU
> speed and does not handle frequency changes (though I think it should be
> possible to fix this purely in software, no-one seems to care though).
> The TTC can use the prescaler to adjust the timing when the CPU speed changes.
> But if you use AMP, frequency scaling will affect both cores, so you
> probably cannot use it anyway.

Thanks for this information, Mike.  I'm probably not using dynamic
clocks since I'm using both the global arm timer and AMP.  In what
cases are dynamic clocks used?  Just for my information, how are they
enabled?

> For AMP, I assigned the TTC1 interrupts to the remoteproc. I also add GPIO
> "hogs" for all GPIO signals it uses. That way, the AMP firmware doesn't need
> to modify various race-condition prone registers.

Could you explain about how GPIO hogs eliminate dealing with
race-condition prone registers?  Which registers are prone to race
conditions in the first place?