82845PE Datasheet, PDF (99/176 Pages) Intel Corporation – 82845GE Graphics and Memory Controller Hub (GMCH) and 82845PE Memory Controller Hub (MCH)

Register Description
3.5.4.2
DRTC—DRAM Read Throttling Control Register (Device 6)
Address Offset
Default Value
Access
Size:
D8h
0000000000000000h
R/W, L
64 bits
Bits
Description
63:41
40:28
27:22
21:15
14:3
2:1
0
Intel Reserved.
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.
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).
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.
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.
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.
Intel^® 82845GE/82845PE Datasheet
99