Changeset b06279d in rtems for c/ACKNOWLEDGEMENTS

May 7, 1999, 4:28:43 PM (23 years ago)
Joel Sherrill <joel.sherrill@…>
4.10, 4.11, 4.8, 4.9, 5, master

Bug fix from Gunter Magin <magin@…>:

in libcpu/powerpc/mpc860/clock/clock.c:InstallClock() the reload value for
the PIT is defined as:

pit_value = (BSP_Configuration.microseconds_per_tick *

Cpu_table.clicks_per_usec) - 1 ;

What exactly is a tick, and what is a click?

My confusion stems from the fact, that Jay defines clicks_per_usec to 1
which is correct for his configuration, where a 4MHz clock is predivided
by 4 and then fed to the PIT. So I assume a "click" is just the period of
the PIT input frequency.

However, our HW config seems to have 32.768 kHz crystal input for PIT.
Mandatory division by 4 means 8.196kHz (122usec) at the PIT.

I think, the above assignment should read:

pit_value = (BSP_Configuration.microseconds_per_tick /

Cpu_table.clicks_per_usec) - 1;

where I can define Cpu_table.clicks_per_usec in bspstart.c to 122
(clicks_per_usec). That would lead to a PIT reload value of
10000/122 - 1 = 81 to reach a 10ms "tick" period.

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