
4-4
BUS PROTOCOL
symmetric agent currently owns the bus (“idle” state). The Pentium Pro processor will enter the
idle state after AERR#, BINIT# and RESET#. The notion of idle state enables a shorter, two-
clock arbitration latency from bus request to its ownership. The notion of busy state enables bus
parking but increases arbitration latency to a minimum of four clocks due to a handshake with
the current symmetric owner. Bus parking means that the current bus owner maintains bus own-
ership even if it currently does not have a pending transaction. If a transaction becomes pending
before that bus owner relinquishes bus ownership, it can drive the transaction without having to
arbitrate for the bus. The Pentium Pro processor implements bus parking.
4.1.3.1.1.
Agent ID
An agent’s Agent ID is determined at reset and cannot change without the assertion of RESET#.
The Agent ID is unique for every symmetric agent.
4.1.3.1.2.
Rotating ID
The Rotating ID points to the agent that will be the lowest priority agent in the next arbitration
event with active requests, (this is the Agent ID of the current symmetric bus owner). All sym-
metric agents maintain the same Rotating ID. The Rotating ID is initialized to 3 at reset. It is
assigned the Agent ID of the new symmetric owner after an arbitration event so that the new
owner becomes the lowest priority agent on the next arbitration event.
4.1.3.1.3.
Symmetric Ownership State
The symmetric ownership state is reset to idle on an arbitration reset. The state becomes busy
when any symmetric agent completes the Arbitration Phase and becomes symmetric owner. The
state remains busy while the current symmetric owner retains bus ownership or transfers it to a
different symmetric agent on the next arbitration event. When the state is busy, the Rotating ID
is the same as the symmetric owner Agent ID. When the state is idle, the Rotating ID is the same
as the last symmetric owner Agent ID. Note that the symmetric ownership state refers only to
the symmetric bus owner. The priority agent can have actual physical ownership of the request
bus, even while the state is busy and there is also a symmetric bus owner.
4.1.3.2.
REQUEST STALL PROTOCOL
Any bus agent can stop all agents from issuing transactions via the BNR# (block next request)
pin. This is typically done when the agent has one free request buffer remaining and cannot rely
on the In-order Queue depth limit to sufficiently limit the number of transactions initiated on the
bus. BNR# can be used to stall transactions for a user-defined amount of time, or it can be used
to throttle the frequency of the transactions issued to the bus. BNR# can also be used to prevent
any transactions from being issued after RESET# or BINIT# to block transactions while bus
agents initialize themselves. For debugging, performance monitoring, or test purposes, an agent
can assert BNR# to issue one transaction to the bus at a time (no pipelining). When stalling the
bus, the stalling condition must be able to clear without requiring access to the bus.
Содержание Pentium Pro Family
Страница 17: ...1 Component Introduction ...
Страница 26: ...2 Pentium Pro Processor Architecture Overview ...
Страница 27: ......
Страница 36: ...3 Bus Overview ...
Страница 62: ...4 Bus Protocol ...
Страница 105: ...5 Bus Transactions and Operations ...
Страница 126: ...6 Range Registers ...
Страница 131: ...7 Cache Protocol ...
Страница 135: ...8 Data Integrity ...
Страница 148: ...9 Configuration ...
Страница 161: ...10 Pentium Pro Processor Test Access Port TAP ...
Страница 172: ...11 Electrical Specifications ...
Страница 201: ...12 GTL Interface Specification ...
Страница 229: ...13 3 3V Tolerant Signal Quality Specifications ...
Страница 233: ...14 Thermal Specifications ...
Страница 239: ...15 Mechanical Specifications ...
Страница 241: ...15 2 MECHANICAL SPECIFICATIONS s Figure 15 1 Package Dimensions Bottom View ...
Страница 252: ...16 Tools ...
Страница 260: ...16 8 TOOLS Figure 16 4 Generic MP System Layout for Debug Port Connection ...
Страница 264: ...17 OverDrive Processor Socket Specification ...
Страница 290: ...A Signals Reference ...
Страница 320: ...Index ...
Страница 328: ......