Communication Processor Module
16-501 MPC823e REFERENCE MANUAL MOTOROLA
CPIC
COMMUNICATION
16
PROCESSOR MODULE
16.15.2.1 USB AND SCCx RELATIVE PRIORITY. The relative priority between the USB
and SCCs is programmable and can be dynamically changed. In Table 16-45 there is no
entry for the USB and SCCs, but rather there are entries for SCCa, SCCb, SCCc, and SCCd
because each one of them can be mapped to any of these locations. This is programmed in
the CICR and can be dynamically changed. You can use this on-the-fly capability to
implement a rotating priority.
In addition, there are two ways to group the locations of the SCCa, SCCb, SCCc, and SCCd
entries—group and spread. In the group scheme, the USB and SCCs are all grouped
together at the top of the priority table, ahead of most of the other CPM interrupt sources.
This scheme is ideal for applications in which the USB and SCCs function at a very high data
rate and interrupt latency is very important. In the spread scheme, USB and SCCs priorities
are spread over the table, so other sources can have lower interrupt latencies than the USB
and SCCs. This scheme is also programmed in the CICR, but it cannot be dynamically
modified.
16.15.2.2 HIGHEST PRIORITY INTERRUPT. In addition to the USB and SCCs relative
priority option, you can choose one interrupt source to be of the highest priority. This highest
priority interrupt is still within the same interrupt level as the rest of the CPIC interrupts, but
is serviced prior to any other interrupt in the table. If the highest priority feature is not used,
select PC15 to be the highest priority interrupt and no modifications to the standard interrupt
priority order will be made. This highest priority source is dynamically programmable in the
CICR and it allows you to change a normally low priority source into a high priority source
for a certain period of time.
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