29 September 1997 – Subject To Change
Internal Processor Registers
5–19
Instruction Fetch/Decode Unit and Branch Unit (IDU) IPRs
5.1.19 Interrupt ID (INTID) Register (111)
INTID is a read-only register that is written by hardware with the target IPL of the
highest priority pending interrupt. The hardware recognizes an interrupt if the IPL
being read is greater than the IPL given by IPLR<04:00>.
Interrupt service routines may use the value of this register to determine the cause of
the interrupt. PALcode, for the interrupt service, must ensure that the IPL in INTID
is greater than the IPL specified by IPLR. This restriction is required because a level-
sensitive hardware interrupt may disappear before the interrupt service routine is
entered (passive release).
The contents of INTID are not correct on a HALT interrupt because this particular
interrupt does not have a target IPL at which it can be masked. When a HALT inter-
rupt occurs, INTID indicates the next highest priority pending interrupt. PALcode
for interrupt service must check the interrupt summary register (ISR) to determine if
a HALT interrupt has occurred. Figure 5–18 shows the INTID register format.
Figure 5–18 Interrupt ID (INTID) Register
00
04
05
31
INTID<4:0>
32
63
RAZ/IGN
LJ-03490.AI4
RAZ/IGN