170 AMD Geode™ LX Processors Data Book
CPU Core Register Descriptions
33234H
Region Properties
The region properties consist of an 8-bit field as shown in Table 5-15. Table 5-16 and Table 5-17 describe the various region
properties effects on read and write operations. Note that the cache is always interrogated even in regions that are not
cacheable, and read hits are serviced from the cache while write hits update the cache and are sent to the bus using the
region’s write semantics.
Table 5-15. Region Properties Register Map
76543210
(RSVD)
Reserved
WS
(Write-serialize)
WC
(Write-combine)
WT
(Write-through)
WP
(Write-protect)
WA
(Write-allocate)
CD
(Cache Disable)
Table 5-16. Read Operations vs. Region Properties
WS WC WT WP WA CD Description
0xxxx0Cacheable. Read misses cause a cache line to be allocated.
1xxxx0Undefined State. Unpredictable behavior occurs.
xxxxx1Uncacheable. Reads are sent unmodified to the bus. Cache is still interro-
gated and provides data for read hits. Used for accessing memory-mapped
devices.
Note: “x” indicates setting or clearing this bit has no effect.
Table 5-17. Write Operations vs. Region Properties
WS WC WT WP WA CD Description
xxx1xxWrite-protected. Writes to the region are discarded.
1xxxx0Undefined State. Unpredictable behavior occurs.
x1xxx0Undefined State. Unpredictable behavior occurs.
xxxx11Undefined State. Unpredictable behavior occurs.
000000Write-back Cacheable. Write misses are sent to the bus, a cache line is not
allocated on a write miss.
000010Write-back Cacheable/Write-allocate. Write misses allocate a line in the
cache.
0010x0Write-through cacheable. Write misses do not allocate a line in the cache.
Write hits update the cache but do not mark the line as dirty. All writes are sent
to the bus.
000001Uncacheable. All writes are sent to the bus in strict program order without any
combining. Write hits still update the cache. Traditionally used for accessing
memory-mapped devices (but see write-burstable below).
100001Uncacheable. All writes are sent to the bus in strict program order without any
combining. Write hits still update the cache. Traditionally used for accessing
memory-mapped devices (but see write-burstable below).
Write-serialize. Limit the number of outstanding writes to the value of the
WSREQ field in DM_CONFIG0_MSR (MSR 00001800h[46:44]).
010001Write-combined (uncacheable). Writes to the same cache line may be com-
bined. Multiple writes to the same byte results in a single write with the last
value specified. Write order is not preserved; ideal for use with frame buffers.