
2-14
PowerPC Microprocessor Family: The Bus Interface for 32-Bit Microprocessors
Write
with kill
0
010
Yes
Yes
Don’t care S or I
Snoop push
6
from write-back buffer (read or read-
atomic)—The data cache has a shared copy if the
buffer held a block clean (
dcbst
) transaction. If it
held a block flush (
dcbf
) or cache write-back
transaction, the cache has no valid copy after the
transaction. To know if the processor kept a shared
copy or invalidated this block, this transaction must
be ARTRYd. If it originated from the write-back
buffers and no new snoops occur, the transaction
returns as the next TS and indicates a DCBF,
DCBST, or write-back WT/TC code. If it returns as a
snoop push read, it came from the data cache.
100
Yes
No
Don’t care I
Snoop push
6
directly from data cache (RWITM,
RWITM-atomic, flush, write w/flush, write w/flush-
atomic, or kill)
100
Yes
Yes
Don’t care I
Snoop push
6
from write-back buffers (RWITM,
RWITM-atomic, flush, write w/flush-atomic, write
w/flush, write w/kill, or kill)
000
Yes
No
Don’t care M, E, I
Snoop push
6
from data cache (clean or RWNITC)—
The clean or RWNITC snoop changes the data
cache state to E when the modified block is put in
the snoop-push buffer. Before the buffer completes
its address tenure, the cache state can be changed
to M by a store or to I by either a
dcbi
instruction or
cache miss.
000
Yes
Yes
Don’t care M, E, I
(
dcbst
in buffer)
I (cache
write-
back or
dcbf
in
buffer)
Snoop push
6
from write-back buffers (clean or
RWNITC)—If this snoop hit on a block-flush (
dcbf
)
or a cache write-back in the write-back buffers, the
cache does not have a valid copy of this address
after this transaction. If this snoop hits a block-store
(
dcbst
) in the write-back buffers, the processor can
keep an exclusive copy of the cache block.
Kill block x
100
Never
No
Don’t care I
Kill block deallocate (
dcbi
)
1
000
M
Kill block and allocate no castout required (
dcbz
)
1
001
Kill block and allocate castout required (
dcbz
)
1
000
Kill block; write to block marked S
Table 2-5. Transfer Code Signal Encoding for PowerPC 604 Processor (Continued)
Transfer
Type
WT
1
TC
[0–2]
BR
Asserted
From
Write-
Back
Buffer
TS after
ARTRYd
Snoop
4
Final
Cache
State
5
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