RTEMS and clock frequency specification

Joel Sherrill joel.sherrill at OARcorp.com
Sun Nov 8 18:27:14 UTC 2009

Thomas Dörfler wrote:
> Hi,
> recently I once again hit the problem (with a powerpc board) that the
> "standard" resolution to specify the system bus (and decrementer) clock
> rate is in microseconds.
> The hardware I have here has a 133MHz bus clock and the DEC clock is
> divided by 16, which results in a decrement rate of 8.325MHz. Since the
> standard decrementer driver expects its input clock to be specified in
> "ticks_per_microsecond", we would get a timing error of 4%, which is way
> beyond the acceptable deviation.
> Wouldn't it be time to move to a higher resolution? I really would
> recommend to switch to "ticks_per_second" which would allow us to be
> more precise?
Seems reasonable but the question is 4.10 or the next release.
I hope we are close to 4.10.

At one point, this was in milliseconds (yes that was a LONG time
ago).  If everyone is using the macros to configure a system and
the clock drivers are using macros to get the value, it
should be a fairly painless to change.  But it impacts every BSP
which carries some risk.

> wkr,
> Thomas.

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