4-29
BUS PROTOCOL
4.5.2.3.
IMPLICIT WRITEBACK ON A READ TRANSACTION
Figure 4-16 shows a read transaction with an implicit writeback. TRDY# is asserted in this op-
eration because there is writeback data to transfer. Note that the implicit writeback response
must be asserted exactly one clock after valid TRDY# assertion is sampled. That is, TRDY# is
sampled active and DBSY# is sampled inactive.
A transaction is issued in T1. The REQa0# pin indicates a read transaction, so TRDY# is as-
sumed not needed for this transaction.
But snoop results observed in T6 indicate that an implicit writeback will occur (HITM# is as-
serted), therefore a TRDY# assertion is needed. Since the response for the previous transaction
is complete, and no request initiated TRDY# assertion is needed, TRDY# for the implicit write-
back is asserted in T7. (TRDY# assertion due to an implicit writeback is called a snoop initiated
TRDY#.) Since DBSY# is observed inactive in T7, TRDY# can be deasserted in one clock in
T8, but need not be deasserted until the response is driven on RS[2:0]#.
In T9, one clock after the observation of active TRDY# with inactive DBSY# for the implicit
writeback, the Implicit Writeback Response must be driven on RS[2:0]# and the data is driven
on the data bus. This makes the data transfer and response behave like both a read (for the re-
questing agent) and a write (for the addressed agent).
Figure 4-16. RS[2:0]# Activation with Snoop Initiated TRDY#
CLK
DBSY#
TRDY#
HITM#
RS[2:0]#
{scnt}
1
2
3
4
5
6
7
8
9
10
11
12
ADS#
{rcnt}
REQ0#
0
0
1
1
1
1
0
0
0
0
0
0
0
0
1
1
1
1
1
1
1
1
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: ......