Hardware Initialization; Memory Scrubbing; Scrubbing Time - Intel 460GX Software Developer’s Manual

5.5.3

Hardware Initialization

In order to decrease boot time of systems with large amounts of DRAM installed, hardware
initialization of memory will be supported. Since multiple rows will be initialized simultaneously,
the memory system will be able to initialize to 0 about 8 times faster than having the processor
looping through memory with writes. The MDC will force all zeroes on the data lines, with good
ECC, and the MAC will cycle through the memory addresses generating writes. The main limiter
to the number of rows being simultaneously initialized is current draw on the DRAM. One row
from each of the 4 stacks across the 2 cards will be initialized concurrently.
5.5.4

Memory Scrubbing

Scrubbing is the operation of walking through all installed DRAM and looking for errors. Each line
is read and then written back, whether there is an error or not. Within the SAC there is an engine to
generate addresses to be placed in the memory queue. These addresses are placed directly into the
SAC memory queue and are not snooped on the system bus, nor are they checked for address
conflicts, since the read-modify-write is treated as an atomic operation.
A scrub address is generated every 65K (65536) clocks. For a system with 32 GB of memory, this
would walk through all memory every 3.2 days. The following table shows the approximate time to
scrub memory based on memory size. Scrubbing may be disabled through a configuration bit.
Table 5-4. Scrubbing Time
Memory Size
64 MB
128 MB
256 MB
512 MB
1 GB
2 GB
4 GB
8 GB
16 GB
32 GB
64 GB
Intel® 460GX Chipset Software Developer's Manual
Time to Scrub
10 minutes
20 minutes
40 minutes
1.2 hours
3 hours
5 hours
10 hours
20 hours
1.6 days
3.2 days
6.4 days
Memory Subsystem
5-7