RTEMS and clock frequency specification

Thomas Dörfler Thomas.Doerfler at embedded-brains.de
Sun Nov 8 18:04:07 UTC 2009


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?



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