Kind of strange interrupt behavior

[Till Straumann]

Is the BSP you are using part of the official RTEMS tree
- i.e. what BSP are you using?

Other questions, about the timers (i.e. the 1Hz irq source
and the system clock timer):

- Are their clock signals synchronous,
   i.e. are they derived from some common source?
- How accurate
   are the timing intervals, i.e. are the timer periods determined
   by the hardware only or does the software have to restart them
   after expiration?
- What is the priority of your 1Hz timer IRQ compared to the
   system clock IRQ (higher, same or lower)? How are nested
   interrupts handled by your hardware (and your BSP)?

(My first, wild guess would be that the clocks beat against each other
with a periodicity of ~20min and that the 1Hz timer hits the
system clock [which is probably at a higher priority] while the
clock handler is working, resulting in a high latency.)

Some suggestions:

- you could run your test on a completely idle system
   (only the idle task should be running).
- try to run the test without a system clock driver.

Do you still observe the 20min periodicity?

-- Till.