MOTOROLA
Chapter 2. PowerPC Processor Core
2-15
Programming Model
15
NHR
Not hard reset (software-use only)Helps software distinguish a hard reset from a soft reset.
0 A hard reset occurred if software had previously set this bit.
1 A hard reset has not occurred. If software sets this bit after a hard reset, when a reset occurs
and this bit remains set, software can tell it was a soft reset.
16
ICE
Instruction cache enable
2
0The instruction cache is neither accessed nor updated. All pages are accessed as if they were
marked cache-inhibited (WIM = X1X). Potential cache accesses from the bus (snoop and cache
operations) are ignored. In the disabled state for the L1 caches, the cache tag state bits are
ignored, and all accesses are propagated to the bus as single-beat transactions.For these
transactions, however, the processor reects the original state of the I bit (from the MMU) to the
peripheral logic block, regardless of cache disabled status.
ICE is zero at power-up.
1 The instruction cache is enabled
17
DCE
Data cache enable
2
0 The data cache is neither accessed nor updated. All pages are accessed as if they were
marked cache-inhibited (WIM = X1X). Potential cache accesses from the bus (snoop and
cache operations) are ignored. In the disabled state for the L1 caches, the cache tag state bits
are ignored and all accesses are propagated to the bus as single-beat transactions.
For those transactions, however, the processor reects the original state of the I bit (from the
MMU) to the peripheral logic block, regardless of cache disabled status.
ICE is zero at power-up.
1 The data cache is enabled.
18
ILOCK
Instruction cache lock
0 Normal operation
1 Instruction cache is locked. A locked cache supplies data normally on a hit, but an access is
treated as a cache-inhibited transaction on a miss. On a miss, the transaction to the bus is
single-beat.To prevent locking during a cache access, an isync must precede the setting of
ILOCK.
19
DLOCK
Data cache lock
0 Normal operation
1 Data cache is locked. A locked cache supplies data normally on a hit but an access is treated
as a cache-inhibited transaction on a miss. On a miss, the transaction to the bus is single-
beat.
A snoop hit to a locked L1 data cache performs as if the cache were not locked. A cache block
invalidated by a snoop remains invalid until the cache is unlocked.
To prevent locking during a cache access, a sync must precede the setting of DLOCK.
20
ICFI
Instruction cache ash invalidate
2
0 The instruction cache is not invalidated. The bit is cleared when the invalidation operation
begins (usually the next cycle after the write operation to the register). The instruction cache
must be enabled for the invalidation to occur.
1 An invalidate operation is issued that marks the state of each instruction cache block as invalid
without writing back modiTed cache blocks to memory. Cache access is blocked during this
time. Accesses to the cache from the peripheral logic bus are signaled as a miss during
invalidate-all operations. Setting ICFI clears all the valid bits of the blocks and the PLRU bits to
point to way L0 of each set. Once this ash invalidate bit is set through an mtspr instruction,
hardware automatically resets this bit in the next cycle (provided that the corresponding cache
enable bit is set in HID0).
Table 2-1. HID0 Field Descriptions (Continued)
Bits
Name
Description