I've just confirmed that calling _task_stop_preemption() from my main task (priority 11) prevents my 100mS timer interrupt service routine from being called (priority 2). The MQX RTOS Reference Manual description of _task_stop_preemption() says that "Interrupts are still handled" (Rev. 3 01/2010, section 2.1.286, page 383). I'm using MQX 188.8.131.52. Am I misunderstanding this perhaps? Has anyone else seen this behavior? Maybe only external GPIO type interrupts continue to be serviced? My 100mS Timer interrupt updates leds on my project and I think it looks bad when a "Run" led stalls (even briefly). Any ideas? Thanks!