82845PE Datasheet, PDF (98/176 Pages) Intel Corporation – 82845GE Graphics and Memory Controller Hub (GMCH) and 82845PE Memory Controller Hub (MCH)

Register Description
3.5.4
3.5.4.1
Device 6 Registers
Device 6 registers are Intel Reserved, except for the following two registers.
DWTC—DRAM Write Throttling Control Register (Device 6)
Address Offset
Default Value
Access
Size:
D0–D7h
0000000000000000h
R/W, L
64 bits
Bits
63:41
40:28
27:22
21:15
14:3
2:1
0
Description
Intel Reserved.
Global Write Hexword Threshold (GWHT). The thirteen-bit value held in this field is multiplied by
2¹⁵ to arrive at the number of hexwords that must be written within the Global DRAM Write Sampling
Window to cause the throttling mechanism to be invoked.
Write Throttle Time (WTT). This value provides a multiplier between 0 and 63 which specifies how
long throttling remains in effect as a number of Global DRAM Write Sampling Windows. For
example, if GDWSW is programmed to 1000_0000b and WTT is set to 01_0000b, then throttling will
be performed for 8192*10⁵ host clocks (at 100 MHz) seconds once invoked
(128 * 4*10⁵ host clocks * 16).
Write Throttle Monitoring Window (WTMW). 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 writes are monitored during this window. If the number of hexwords written during
the window reaches the Write Throttle Hexword Maximum, then write requests are blocked for the
remainder of the window.
Write Throttle Hexword Maximum (WTHM). The Write Throttle Hexword Maximum defines the
maximum number of hexwords between 0-4095 which are permitted to be written to DRAM within
one Write Throttle Monitoring Window.
Write Throttle Mode ((WTMode).
00 = Throttling via Counters and Hardware throttle_on signal mechanisms disabled.
01 = Reserved
10 = Counter mechanism controlled through GDWSW and GWHT is enabled. When the threshold
set in GDWSW and GWHT is reached, throttling start/stop cycles occur based on the settings
in WTT, WTMWand WTHM.
11 = Reserved
START Write Throttle (SWT). Software writes to this bit to start and stop write throttling.
0 = Write throttling stops and the counters associated with WTMW and WTHM are reset.
1 = Write throttling begins based on the settings in WTMW and WTHM, and remains in effect until
this bit is reset to 0.
98
Intel^® 82845GE/82845PE Datasheet