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Register Description
R
72 Intel
®
82845 MCH for SDR Datasheet
3.5.32 LPTT—AGP Low Priority Transaction Timer Register
(Device 0)
Address Offset: BDh
Default Value: 00h
Access: R/W
Size: 8 bits
LPTT is an 8-bit register similar in function to AMTT. This register is used to control the
minimum tenure on the AGP for low-priority data transactions (both reads and writes) issued using
PIPE# or SB mechanisms.
The number of clocks programmed in the LPTT represents the guaranteed time slice (measured in
66 MHz clocks) allotted to the current low priority AGP transaction data transfer state. This does
not necessarily apply to a single transaction but it can span over multiple low-priority transactions
of the same type. After this time expires, the AGP arbiter may grant the bus to another agent if
there is a pending request. The LPTT does not apply in the case of high-priority request where
ownership is transferred directly to high-priority requesting queue. The default value of LPTT is
00h and disables this function. The LPTT value can be programmed with 8-clock granularity. For
example, if the LPTT is programmed to 10h, the selected value corresponds to the time period of
16 AGP (66 MHz) clocks.
Bit Description
7:3 Low Priority Transaction Timer Count Value (LPTTC). The number of clocks programmed in
these bits represents the guaranteed time slice (measured in eight 66 MHz clock granularity)
allotted to the current low priority AGP transaction data transfer state.
2:0 Reserved.