
4-20
PowerPC Microprocessor Family: The Bus Interface for 32-Bit Microprocessors
Table 4-7. Differences in Implementation of Bus Operations
Bus Operation
Differences
Clean block
The 603 does not broadcast or snoop clean block operations.
Flush block
The 603 does not broadcast or snoop flush block or implement SHD.
Write with flush,
Write with flush atomic
In the 601, HID0[31] controls whether HP_SNP_REQ specifies high-priority operations.
Kill block
The 603 does not broadcast or snoop kill.
Write with kill
—
Read, read atomic
The 603 does not implement SHD and S state.
Read with Intent to
modify (RWITM)
—
TLB invalidate
A snooping 604 also asserts ARTRY when it has a pending TLB invalidate operation and a
second TLB invalidate operation is detected. The 601 uses the
sync
instruction to
synchronize TLBIE operations; the 603 and 604 use
tlbsync
.
SYNC
The PowerPC architecture permits data accesses from more than one instruction to be
combined for cache-inhibited operations, except when the accesses are separated by a
sync
instruction, or by an
eieio
instruction when the page or block is also designated as guarded.
This combined access capability is not implemented on the 603e.
The 603 does not broadcast or snoop SYNC.
A SYNC operation is also generated by the
eieio
instruction on the 601.
TLBSYNC
A 604 seeing
tlbsync
, asserts ARTRY if any pending operations are based on an invalidated
TLB. The 603 does not broadcast or snoop
tlbsync
. The 601 does not implement the
tlbsync
instruction and does not generate this bus operation.
EIEIO
The 603 does not broadcast or snoop EIEIO.
The
eieio
is treated as a no-op by the 603e.
ICBI
The 603 does not broadcast or snoop ICBI. The
icbi
causes the 601 to broadcast a kill
operation to the bus.
Read with no intent to
cache (RWNITC)
Read with no intent to cache (RWNITC) operations are issued by a bus-attached device as
TT[0–4] = 0b01011. The 603 and 604 snoop this and, if they get a cache hit on a block
marked M, push the block and mark it E (the ordinary response would be to push and mark it
S in 604 and push and invalidate for 603). For a graphics adapter that reads display data from
memory, this data may be in the processor’s cache and the subject of frequent updates.
Because it has no S state, the 603 handles some operations differently.
XFERDATA
—
I/O reply
The I/O reply operation serves as the final bus operation in the series of bus operations that
service direct-store interface operation. The 603e processors do not perform these
operations because they do not implement the direct-store facility.