Embedded Systems Design, 2nd Edition

44 Embedded systems design

To prevent an interrupt request generating multiple ac-

knowledgements, the internal interrupt mask is raised to the

interrupt level, effectively masking any further requests. Only if a

higher level interrupt occurs will the processor nest its interrupt

service routines. The interrupt service routine must clear the

interrupt source and thus remove the request before returning to

normal execution. If another interrupt is pending from a different

source, it will be recognised and cause another acknowledgement

to occur.

Error recovery and control signals

There are three signals associated with error control and

recovery. The bus ...