The format of an ASR is similar to that of an ISR
with the following exceptions:
ISRs are scheduled by the processor hardware. ASRs are
scheduled by RTEMS.
ISRs do not execute in the context of a task and may
invoke only a subset of directives. ASRs execute in the context
of a task and may execute any directive.
When an ISR is invoked, it is passed the vector number
as its argument. When an ASR is invoked, it is passed the
signal set as its argument.
An ASR has a task mode which can be different from that
of the task. An ISR does not execute as a task and, as a
result, does not have a task mode.
RTEMS Ada User's Guide