TC1796
System Units (Vol. 1 of 2)
Interrupt System
User’s Manual
14-9
V2.0, 2007-07
Interrupt, V2.0
IE
8
rwh
Global Interrupt Enable Bit
The interrupt enable bit globally enables the CPU
service request system. Whether or not a service
request is delivered to the CPU depends on the
individual Service Request Enable Bits (SRE) in the
SRNs, and the current state of the CPU.
IE is automatically updated by hardware on entry and
exit of an Interrupt Service Routine (ISR).
IE is cleared to 0 when an interrupt is taken, and is
restored to the previous value when the ISR executes
an RFE instruction to terminate itself.
IE can also be updated through the execution of the
ENABLE, DISABLE, MTCR, and BISR instructions.
0
B
Interrupt system is globally disabled
1
B
Interrupt system is globally enabled
PIPN
[23:16] rh
Pending Interrupt Priority Number
PIPN is a read-only bit field that is updated by the ICU
at the end of each interrupt arbitration process. It
indicates the priority number of the pending service
request. PIPN is set to 0 when no request is pending,
and at the beginning of each new arbitration process.
00
H
No valid pending request
YY
H
A request with priority YY
H
is pending
CARBCYC
[25:24] rw
Number of Arbitration Cycles
CARBCYC controls the number of arbitration cycles
used to determine the request with the highest priority.
00
B
4 arbitration cycles (default)
01
B
3 arbitration cycles
10
B
2 arbitration cycles
11
B
1 arbitration cycle
CONECYC
26
rw
Number of Clocks per Arbitration Cycle Control
The CONECYC bit determines the number of system
clocks per arbitration cycle. This bit should be set to 1
only for system designs utilizing low system clock
frequencies.
0
B
2 clocks per arbitration cycle (default)
1
B
1 clock per arbitration cycle
0
[15:9],
[31:27]
r
Reserved
Read as 0; should be written with 0.
Field
Bits
Type Description