845GL datasheet(103/193 Pages) INTEL

103 / 193 page

Intel® 82845G/82845GL/82845GV GMCH Datasheet

103

3.5.4.2

DRTC—DRAM Read Throttling Control Register (Device 6)

Address Offset

D8h

Default Value

0000000000000000h

Access

R/W, L

Size:

64 bits

Bits

Description

63:41

Intel Reserved.

40:28

Global Read Hexword Threshold (GRHT).

The thirteen-bit value held in this field is multiplied by

2 15 to arrive at the number of hexwords that must be read within the Global DRAM Read Sampling

Window in order to cause the throttling mechanism to be invoked.

27:22

Read Throttle Time (RTT).

This value provides a multiplier between 0 and 63 which specifies how

long Counter based read throttling remains in effect as a number of Global DRAM Read Sampling

Windows. For example, if GDRSW is programmed to 1000_0000b and RTT is set to 01_0000b, then

read throttling will be performed for 8192*105 host clocks (at 100 MHz) seconds once invoked

(128 * 4*105 host clocks * 16).

21:15

Read Throttle Monitoring Window (RTMW).

The value in this register is padded with 4 zeros to

specify a window of 0–2047 host clocks with 16 clock granularity. While the throttling mechanism is

invoked, DRAM reads are monitored during this window. If the number of hexwords read during the

window reaches the Read Throttle Hexword Maximum, read requests are blocked for the remainder

of the window.

14:3

Read Throttle Hexword Maximum (RTHM).

The Read Throttle Hexword Maximum defines the

maximum number of hexwords between 0–4095 which are permitted to be read from DRAM within

one Read Throttle Monitoring Window.

2:1

Read Throttle Mode (RTMode).

00 = Throttling via Counters and Hardware throttle_on signal mechanisms Disabled.

01 = Reserved

10 = Counter mechanism controlled through GDRSW and GRHT is enabled. When the threshold set

in GDRSW and GRHT is reached, throttling start/stop cycles occur based on the settings in

RTT, RTMW, and RTHM.

11 = Reserved

START Read Throttle (SRT).

Software writes to this bit to start and stop read throttling.

0 = Read throttling stops and the counters associated with RTMW and RTHM are reset.

1 = Read throttling begins based on the settings in RTMW and RTHM, and remains in effect until

this bit is reset to 0.

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