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version 2011-09-20

CRIT : start CRITical section

This instruction temporarily disables interrupts during the next instructions. The length of this critical section is given by the immediate value in si4, the register fields are ignored. The maximum length is 16 instructions.

Software traps are not prevented, this is useful only to provide atomic operations (like complex semaphores) if they can't be managed through the Special Registers.

When another CRIT instruction is found during a critical section, the latter is aborted, IRQs are handled (this can cause context switches) then the new critical section is started.