
3-20
MPC603e & EC603e RISC Microprocessors User's Manual
MOTOROLA
Table 3-6. Response to Bus Transactions
Snooped Transaction
603e Response
Clean block
No action is taken.
Flush block
No action is taken.
Write-with-flush
Write-with-flush-atomic
Write-with-flush and write-with-flush-atomic operations occur after the processor issues
a store or
stwcx.
instruction, respectively.
If the addressed block is in the exclusive state, the address snoop forces the state of
the addressed block to invalid.
If the addressed block is in the modified state, the address snoop causes ARTRY to
be asserted and initiates a push of the modified block out of the cache and changes
the state of the block to invalid.
The execution of an
stwcx.
instruction cancels the reservation associated with any
address.
Kill block
The kill block operation is an address-only bus transaction initiated when a
dcbz
instruction is executed; when snooped by the 603e, the addressed cache block is
invalidated if in the E state, or flushed to memory and invalidated if in the M state, and
any associated reservation is canceled.
Write-with-kill
In a write-with-kill operation, the processor snoops the cache for a copy of the
addressed block. If one is found, an additional snoop action is initiated internally and the
cache block is forced to the I state, killing modified data that may have been in the block.
Any reservation associated with the block is also canceled.
Read
Read-atomic
The read operation is used by most single-beat and burst read operations on the bus. All
burst reads observed on the bus are snooped as if they were writes, causing the
addressed cache block to be flushed. A read on the bus with the GBL signal asserted
causes the following responses:
If the addressed block in the cache is invalid, the 603e takes no action.
If the addressed block in the cache is in the exclusive state, the block is invalidated.
If the addressed block in the cache is in the modified state, the block is flushed to
memory and the block is invalidated.
If the snooped transaction is a caching-inhibited read, and the block in the cache is in
the exclusive state, the snoop causes no bus activity and the block remains in the
exclusive state. If the block is in the cache in the modified state, the 603e initiates a
push of the modified block out to memory and marks the cache block as exclusive.
Read atomic operations appear on the bus in response to
lwarx
instructions and
generate the same snooping responses as read operations.
Read-with-intent-to-
modify (RWITM)
RWITM-atomic
A RWITM operation is issued to acquire exclusive use of a memory location for the
purpose of modifying it.
If the addressed block is invalid, the 603e takes no action.
If the addressed block in the cache is in the exclusive state, the 603e initiates an
additional snoop action to change the state of the cache block to invalid.
If the addressed block in the cache is in the modified state, the block is flushed to
memory and the block is invalidated.
The RWITM atomic operations appear on the bus in response to
stwcx.
instructions
and are snooped like RWITM instructions.
sync
No action is taken.
TLB invalidate
No action is taken.