[ECOS] CYGACC_CALL_IF_DELAY_US(1000000) fails

Uwe Kindler ukindler@htwm.de
Tue Nov 25 14:09:00 GMT 2003


Hello,

if I call  CYGACC_CALL_IF_DELAY_US(1000000) in order to delay one second,
then this call returns a lot
faster then 1 second. When I debug the code, then I can see, that
HAL_DELAY_US provided by the HAL
is only used if no kernel package is included. HAL_DELAY_US(1000000) works
fine.

If the kernel package is included, the the following calculation takes
place:

// How many ticks total we should wait for.
        usec_ticks = usecs*CYGNUM_KERNEL_COUNTERS_RTC_PERIOD;

The RTC period for the EDOSK board is 20625. The board runs with 33 Mhz and
the 16 Bit timer is driven
with a prescaler of 16 - timer clock is 33Mhz/16 = 2062500. We would like to
interrupt 100 times per second
2062500 / 100 = 20625.

If I now delay 1 second, usec_ticks is calculated usec_tick = 1000000 *
20625 - this is larger than int32.

In the reference manual is written:
While most of the time this function is called with very small values,
occasionally
(particularly in some ethernet drivers) it is called with values of several
seconds.

So what can I do - if I use larger timer prescale values in order to lower
the timer period I will never get exactly 100 Hz for the timer clock.

Best Regards, Uwe


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