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Functional Description
Interrupt Handling
2-16
SYM53C810A Data Manual
I
If the instruction is a JUMP/CALL WHEN/IF
<phase>, the DSP will be updated to the
transfer address before halting.
I
All other instructions may halt before
completion.
Sample Interrupt
Service Routine
T he following is a sample of an interrupt service
routine for the SYM53C810A. It can be repeated
if polling is used, or should be called when the
IRQ/ pin is asserted if hardware interrupts are
used.
1. Read ISTAT.
2. If the INT F bit is set, it must be written to a
one to clear this status.
3. If only the SIP bit is set, read SIST 0 and
SIST 1 to clear the SCSI interrupt condition
and get the SCSI interrupt status. T he bits in
the SIST 0 and SIST 1 tell which SCSI
interrupt(s) occurred and determine what
action is required to service the interrupt(s).
4. If only the DIP bit is set, read the DSTAT to
clear the interrupt condition and get the DMA
interrupt status. T he bits in the DSTAT will
tell which DMA interrupt(s) occurred and
determine what action is required to service
the interrupt(s).
5. If both the SIP and DIP bits are set, read
SIST 0, SIST 1, and DSTAT to clear the SCSI
and DMA interrupt condition and get the
interrupt status. If using 8-bit reads of the
SIST 0, SIST 1, and DSTAT registers to clear
interrupts, insert a 12 CLK delay between the
consecutive reads to ensure that the interrupts
clear properly. Both the SCSI and DMA
interrupt conditions should be handled before
leaving the ISR. It is recommended that the
DMA interrupt be serviced before the SCSI
interrupt, because a serious DMA interrupt
condition could influence how the SCSI
interrupt is acted upon.
6. When using polled interrupts, go back to step
1 before leaving the interrupt service routine,
in case any stacked interrupts moved in when
the first interrupt was cleared. When using
hardware interrupts, the IRQ/ pin will be
asserted again if there are any stacked
interrupts. T his should cause the system to re-
enter the interrupt service routine.