Hello, I have a following situation with Yagarto and AT91SAM7X: Interrupt routine counts interrupts; ... ++signals; ... In main loop, I need to do further processing based on received signals (I want to keep interrupts lightweight, so only minimal amount of work should be done there) ... somevalue = signals*somescaler; signals = 0; ... Now, this is very thread-unsafe. But how can I do this safely with thumb instruction set? No swp in thumb set, and load/store combination isn't very atomic, and the disabling interrupts apparently is troublesome too: I understood that disabling interrupts with AIC_IECR->IDCR causes spurious interrupts, but could that really cause extra interrupts (ISR called twice if it triggers at bad moment) or does that interrupt just get served late? ISR getting server late would be no problem, since I can do necessary processing fast enough to not miss interrupts, but how is the situation exactly? Now, another thing that isn't clear to me is thumb-interwork -mode. In which situations that is needed exactly? For practical example, if I have for example thumb module calling ARM (to access that precious swp for example), how should I do that? Non-interwork thumb-module calls interwork-thumb module that calls ARM module, or how? (that single swp or access to global interrupt flag gets really expensive really fast this way...)