82815 GMCH
R
80
Datasheet
3.4.35.
LPTT—AGP Low Priority Transaction Timer Register
(Device 0: AGP Mode Only)
Address Offset:
BDh
Default Value:
00h
Access:
Read/Write
Size:
8 bits
LPTT is similar in function to AMTT. This register is used to control the minimum tenure on the AGP
for low priority data transaction (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.
7
3
2
0
Low Priority Transaction Timer Count Value
Reserved
Bit
Description
7:3
Low Priority Transaction Timer Count Value.
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.