Was wondering if anyone is familiar with this - I've got the RPi working as an LED controller, sending digital color data 60 times per second to some WS2801 LED controller chips. Everything's working fine - I'm using c++ and the bcm2835 library for GPIO, and the process just sends 3 quick bytes over 2 GPIO pins then sleeps the remainder of the 1/60 sec - except for a weird intermittent problem:
Every minute or two, the Pi will go into a weird pattern where it stalls for 1 second, then resumes for 1 second, stalls for 1 sec, resumes 1 sec, repeating this anywhere from 2 to 30 times before resuming normally. The 1-second on/off is very precise.
Not sure what this stall is exactly - I've got a rapid blink pattern (30 blinks/sec) running to help troubleshoot. Normally the blinks are smooth, except during the stall, where the light is stuck on or off for 1 second intervals - this is how it would behave if GPIO data stopped outputting during the interval, so I assume that's what's happening.
Any ideas? Weirdly when I run "top" to see if it's a background process, the stalls never happen. Only when "top" isn't running.