4-30
BUS PROTOCOL
4.5.2.4.
IMPLICIT WRITEBACK WITH A WRITE TRANSACTION
Figure 4-17 shows a write transaction combined with a hit to a modified line that requires an im-
plicit writeback. This operation has two data transfers and requires two assertions of TRDY#.
The first TRDY# is asserted by the receiver of the write data whenever it is ready to receive the
write data. Once active TRDY# and inactive DBSY# is observed, the first TRDY# is deasserted
to allow the second TRDY#. The second TRDY# is asserted by the receiver whenever it is ready
to receive the writeback data. The second TRDY# may be deasserted when active TRDY# and
inactive DBSY# is sampled or when the response is driven on RS[2:0]#. One clock after obser-
vation of active TRDY# (and inactive DBSY#) for the implicit writeback, the implicit writeback
response is driven on RS[2:0]# at the same time data is driven for the implicit writeback.
In T1, a write transaction is issued as indicated by active ADS# and REQa0#. At this point, the
transaction appears to be a normal write transaction, so TRDY# is asserted 3 clocks later in T4.
TRDY# is deasserted in T5. Since DBSY# was observed inactive in T4, TRDY# can be deas-
serted in one clock as a special optimization to allow a faster implicit writeback TRDY#.
In T5, the snoop results are driven, and in T6, they are observed. In T7, TRDY# is asserted again
for the implicit writeback. TRDY# can be asserted immediately because the TRDY# for the re-
quest initiated data transfer was already deasserted.
In T9, one clock after observation of active TRDY# with inactive DBSY# for the implicit write-
back, TRDY# must be deasserted and the implicit writeback response is driven on RS[2:0]#.
Since DBSY# was observed active in T7, but inactive in T8, TRDY# is deasserted in T9.
Figure 4-17. RS[2:0]# Activation After Two TRDY# Assertions
CLK
DBSY#
TRDY#
HITM#
RS[2:0]#
1
2
3
4
5
6
7
8
9
ADS#
REQa0#
{rcnt}
0
1
1
1
1
1
1
1
1
0
10
11
12
0
0
13
14
0
0
Summary of Contents for Pentium Pro Family
Page 17: ...1 Component Introduction ...
Page 26: ...2 Pentium Pro Processor Architecture Overview ...
Page 27: ......
Page 36: ...3 Bus Overview ...
Page 62: ...4 Bus Protocol ...
Page 105: ...5 Bus Transactions and Operations ...
Page 126: ...6 Range Registers ...
Page 131: ...7 Cache Protocol ...
Page 135: ...8 Data Integrity ...
Page 148: ...9 Configuration ...
Page 161: ...10 Pentium Pro Processor Test Access Port TAP ...
Page 172: ...11 Electrical Specifications ...
Page 201: ...12 GTL Interface Specification ...
Page 229: ...13 3 3V Tolerant Signal Quality Specifications ...
Page 233: ...14 Thermal Specifications ...
Page 239: ...15 Mechanical Specifications ...
Page 241: ...15 2 MECHANICAL SPECIFICATIONS s Figure 15 1 Package Dimensions Bottom View ...
Page 252: ...16 Tools ...
Page 260: ...16 8 TOOLS Figure 16 4 Generic MP System Layout for Debug Port Connection ...
Page 264: ...17 OverDrive Processor Socket Specification ...
Page 290: ...A Signals Reference ...
Page 320: ...Index ...
Page 328: ......