from extintr.c /* * Initialize the soft interrupt masks to block themselves. */ imask[IPL_SOFTCLOCK] = SINT_SERIAL; imask[IPL_SOFTNET] = SINT_NET; imask[IPL_SOFTSERIAL] = SINT_SERIAL; I suppose imask[IPL_SOFTCLOCK] should be initialized to SINT_CLOCK and not something else ? regards, Andreas