82830MP Datasheet, PDF (80/159 Pages) Intel Corporation – Intel 830MP Chipset: 82830MP Graphics and Memory Controller Hub (GMCH-M)

Intel® 830MP Chipset
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used to optimize the performance of the AGP master (using PCI semantics) that performs multiple back-
to-back transactions to fragmented memory ranges (and as a consequence cannot use long burst
transfers). The AMTT mechanism applies to the CPU-AGP/PCI transactions as well and it guarantees to
the CPU a fair share of the AGP/PCI interface bandwidth.
The number of clocks programmed in the AMTT represents the guaranteed time slice (measured in 66-
MHz clocks) allotted to the current agent (either AGP PCI master or Host bridge) after which the AGP
arbiter may grant the bus to another agent. The default value of AMTT is 00h and disables this function.
The AMTT value can be programmed with 8-clock granularity. For example, if the AMTT is
programmed to 18h, then the selected value corresponds to the time period of 24 AGP (66-MHz) clocks.
Bit
Description
7:3 Multi-Transaction Timer Count Value. The number programmed in these bits represents the guaranteed
time slice (measured in eight 66-MHz clock granularity) allotted to the current agent (either AGP PCI master
or Host bridge) after which the AGP arbiter may grant the bus to another agent.
2:0 Reserved
4.5.1.36
LPTTLow Priority Transaction Timer Register - Device #0
Address Offset:
Default Value:
Access:
Size:
BDh
00h
Read/Write
8 bits
LPTT is an 8-bit register similar in a 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
Sideband 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 the 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, then the selected value corresponds to the time period of 16 AGP (66-MHz) clocks.
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
80
Datasheet
298338-001