TC1784
Peripheral Control Processor (PCP)
User´s Manual
10-39
V1.1, 2011-05
PCP, V2.09
To avoid such a deadlock, the PICU performs a special arbitration round as soon as the
PCP queue becomes full. In this arbitration round, only the service request nodes
assigned to the PCP queue are allowed to participate; all service requests from nodes
external to the PCP are excluded, regardless of whether their priorities are higher or
lower than those of the PCP queue. In this way, it is guaranteed that one entry in the PCP
queue gets serviced, freeing one slot in the queue.
The PCP programmer needs to carefully consider this special operation. It ensures that
deadlocks are avoided, but it implies that if too many PCP channel programs post
service requests to the PCP (self-interrupt), the PCP will have to service these rather
than outside interrupt sources. Depending on the priority given to these requests, this
could undermine an otherwise appropriate use of the interrupt priority scheme. It is
recommended that the system be designed such that in most cases, high-priority
numbers can be assigned to these self-interrupts, so that they can win normal arbitration
rounds, avoiding the situation where the PCP queue becomes full.
Note: If the CPU queue is full, the PCP can continue to operate until it needs to post
another service request to the CPU queue.
10.7
PRAM Protection
To allow the PCP to handle system critical tasks it is necessary to ensure that the PCP
can operate properly regardless of a failure in another part of the system or the PCP
itself. this means that it is necessary to protect all or part of the content of the PRAM from
such failures.
By default, after reset, the PRAM can be considered to be a single memory space
writeable both by FPI Masters and by instructions executed by the PCP itself. However
the PCP contains a programmable protection scheme allowing the definition of up to four
memory regions with different protection from FPI PRAM writes and internally generated
PRAM writes. This is illustrated in
below:-
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