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TC1728
Interrupt System
SRR can be set or cleared either by hardware or by software regardless of the state of
the enable bit SRE. However, the request is only forwarded for service if the enable bit
is set. If SRE = 1, a pending service request takes part in the interrupt arbitration of the
service provider selected by the device's TOS bit. If SRE = 0, a pending service request
is excluded from interrupt arbitrations.
SRR is automatically reset by hardware when the service request is acknowledged and
serviced. Software can poll SRR to check for a pending service request. SRR must be
reset by software in this case by writing a 1 to CLRR.
It is not advisable to clear a pending service request flag SRR (writing CLRR = 1) and
enable the corresponding service request node SRN (writing SRE = 1) simultaneously
at the same write access to the Service Request Control Register. If this should happen,
an unintended interrupt request may be generated. Instead of executing one write
access, it is recommended to split the two actions into two consecutive write accesses
to the corresponding Service Request Control Register, starting with the clearing of the
pending interrupt flag and followed by the enabling of the service request node.
13.2.1.5 Type-Of-Service Control (TOS)
There are two service providers for service requests in the TC1728, the CPU and the
PCP. The TOS bit is used to select whether a service request generates an interrupt to
the CPU (TOS = 0) or to the PCP (TOS = 1). Bit 11 of the Service Request Control
Register is read-only, returning 0 when read. Writing to this bit position has no effect.
However, to ensure compatibility with future extensions, bit 11 should always be written
with a 0.
Note that several Service Request Control Registers (e.g. in the PCP) have a hardwired
TOS bit (0 or 1) that cannot be written. These registers can only generate an interrupt to
one dedicated service provider (PCP or CPU).
Note: Before modifying the content of a TOS bit, the corresponding SRN must be
disabled (SRE = 0).
13.2.1.6 Service Request Priority Number (SRPN)
The 8-bit Service Request Priority Number (SRPN) indicates the priority of a service
request with respect to other sources requesting service from the same service provider,
and with respect to the priority of the service provider itself.
Each active source selecting the same service provider must have a unique SRPN value
to differentiate its priority. The special SRPN value of 00
excludes an SRN from taking
H
part in arbitration, regardless of the state of its SRE bit. The SRPN values for active
sources selecting different service providers (CPU vs. PCP) may overlap. If a source is
not active – meaning its SRE bit is 0 – no restrictions are applied to the service request
priority number.
User's Manual
13-6
V1.0, 2011-12
Interrupt, V1.4
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