4-13
BUS PROTOCOL
4.1.4.7.
SYMMETRIC AND PRIORITY BUS EXCHANGE DURING LOCK#
Figure 4-8 illustrates an ownership request made by both a symmetric and a priority agent during
an ongoing indivisible sequence by a symmetric owner. When this is the case, LOCK# takes pri-
ority over BPRI#. That is, the symmetric bus owner does not give up the bus to the priority agent
while it is driving an indivisible locked operation. Note that bus agent 1 can hold bus ownership
even though BPRI# is asserted. Like the BREQ[3:0]# signals, if the priority agent is going to
issue a transaction, BPRI# must not be driven inactive until the clock in which ADS# is driven
asserted.
Before T1, agent 0 owns the bus. In T1, agent 0 initiates the first transaction in a bus locked op-
eration by asserting LOCK# along with request 0a. Also in T1, the priority agent and agent 1
assert BPRI# and BREQ1# respectively to arbitrate for the bus. Agent 0 does not deassert
BREQ0# or LOCK# since it is in the middle of a bus locked operation.
In T7, agent 0 initiates the last transaction in the bus locked operation. At the request’s success-
ful completion the indivisible sequence is complete and agent 0 deasserts LOCK# in T11. Since
BREQ1# is observed active in T10, agent 0 also deasserts BREQ0# in T11 to release symmetric
ownership.
The deassertion of LOCK# is observed by the priority agent in T12 and it begins new-request
generation from T13. The deassertion of BREQ0# is observed by all symmetric agents and they
assign the symmetric ownership to agent 1, the agent with active bus request. In T13, all sym-
metric agents update the Rotating ID to one, the Agent ID of the new symmetric owner.
Figure 4-8. Symmetric and Priority Bus Exchange During LOCK#
CLK
BREQ0#
BREQ1#
BPRI#
LOCK#
ADS#
BREQ2#
BREQ3#
{REQUEST}
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{rotating id}
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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: ......