TC1796
System Units (Vol. 1 of 2)
Peripheral Control Processor (PCP)
User’s Manual
11-35
V2.0, 2007-07
PCP, V2.0
11.5.4.1 Service Request on EXIT Instruction
An implicit PCP service request is issued when the INT field of the EXIT instruction is set
to 1 and the specified condition code, cc_B, of this instruction is true. Such a service
request can be issued to any of the available interrupt buses, depending on the
programmed value in the TOS field of register R6. The PCP examines the TOS field in
register R6 and issues a service request to the appropriate queue of the service request
nodes. Along with this request, it passes the service request priority number stored in the
SRPN field of register R6 to the queue. If the queue has a free entry left, the service
request flag, SRR, of the associated service request register, PCP_SRCx, will be set,
and the service request priority number will be written to the SRPN field of the SRC
register. Please see
for the case there is no free entry in the queue.
Because the desired service request is programmed through the TOS and SRPN fields
in register R6, each channel program can issue its individual service request. Note that
this register needs to be programmed properly if a service request is to be generated by
the EXIT instruction.
11.5.4.2 Service Request on Suspension of Interrupt
An implicit PCP service request is issued when the PCP suspends execution of the
ongoing channel program in favor of a service request with a higher priority. Such a
service request is always issued to the PCP’s own interrupt bus and is stored in one of
the three extended Service Request Nodes (PCP_SCR9, PCP_SRC10, PCPSRC11).
Along with this request, it passes the current channel operating priority (CPPN) as a
SRPN and also the channel number (the original SRPN). The service request flag, SRR,
and the Restart Request flag, RRQ, of the associated service request register,
PCP_SRCx, will be set, the Operating Priority will be written to the SRPN field, and the
channel number will be written to the SRNC field of the SRC register.
Use of the Operating Priority as the SRPN for resumption of the channel program
ensures that during subsequent arbitration rounds the PCP will resume execution of the
suspended channel program at the appropriate time.
The PCP treats an interrupt request with the RRQ bit set in a special fashion. In this case
the PCP clears the interrupt request bit in the appropriate internal Service Request Node
but does not issue an interrupt acknowledge to any external nodes. This prevents the
unwanted clearing of external service requests with an SRPN that matches the priority
of a suspended channel.
Note: The PCP will only suspend channel operation when there are two or more free
service Request Nodes with the appropriate TOS value for the PCP, and one of
the free Service Request Nodes is an Extended Service Request Node. This
allows for the posting of an interrupt request to the PCP on exit from the new
channel program.