6.8.1.2 Data Cache Cachability Register (DCCR)
The DCCR controls the I storage attribute for data accesses and cache management instructions.
Note that the
polarity of the bits in this register is opposite to that of the I attribute
in
the TLB;
DCCR[Sn] = 1 enables caching, while TLB_entry[l] = 1 inhibits caching.
After any reset,
all DCCR bits are set to
O.
No memory regions are cachable. Before memory regions
can be designated as
cachable
in
the DCCR, it is necessary to execute the
dccci
instruction once for
each congruence
class
in
the DCU cache array. This procedure invalidates all congruence classes.
The DCCR can then be reconfigured, and the DCU can begin normal operation.
The PowerPC Architecture does not support memory
models
in
which write-through is enabled and
caching is inhibited.
6.8.1.3 Instruction Cache Cachability Register (ICCR)
The ICCR controls the I storage attribute for instruction fetches. Note that the polarity of the bits
in
this
register is opposite of that of the
I attribute (ICCR[Sn] = 1 enables caching, while TLB_entry[l] = 1
inhibits caching).
After any reset,
all ICCR bits are set to
O.
No memory regions are cachable. Before memory regions
can be designated as
cachable
in
the ICCR, it is necessary to execute the
iccci
instruction. This
invalidates all congruence classes. The ICCR can then be reconfigured, and the ICU can begin
normal operation.
6.8.1.4 Storage Guarded Register (SGR)
The SGR controls the G storage attribute for instruction and data accesses.
This attribute does not affect data accesses; the
PPC405GP does not perform speculative loads
or
stores.
After any reset,
all SGR bits are set to
1,
marking all storage as guarded. For best performance,
system software
should clear the guarded attribute
of
appropriate regions as soon as possible. If
MSR[IR]
=
1,
the G attribute comes from the TLB entry. Attempting to execute from a guarded region
in
translate mode causes an instruction storage interrupt. See "Instruction Storage Interrupt" on
page
10-38 for more information.
6.8.1.5 Storage User-defined 0 Register
(SUOR)
The Storage User-defined 0 Register (SUOR) controls the user-defined
(UO)
storage attribute for
instruction and data accesses.
After any reset,
all
SUOR
bits are set to
O.
6.8.1.6 Storage LiUle-Endian Register (SLER)
The SLER controls the E storage attribute for instruction and data accesses.
This attribute determines the byte ordering of storage.
"Byte Ordering" on page 3-28 provides a
detailed description of byte ordering
in
the IBM PowerPC Embedded Environment.
After any reset,
all SLER bits are set to 0 (big endian).
Preliminary
Memory Management
6-19
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