Intel 64 and IA-32 Architectures Software Developers Manual Volume 3A, System Programming Guide, Part 1

Vol. 3A 10-41
MEMORY CACHE CONTROL
Example 10-6. MemTypeSet Pseudocode
IF CPU_FEATURES.MTRR (* processor supports MTRRs *)
THEN
IF BASE and SIZE are not 4-KByte aligned or size is 0
THEN return INVALID;
FI;
IF (BASE + SIZE) wrap 4-GByte address space
THEN return INVALID;
FI;
IF TYPE is invalid for Pentium 4, Intel Xeon, and P6 family
processors
THEN return UNSUPPORTED;
FI;
IF TYPE is WC and not supported
THEN return UNSUPPORTED;
FI;
IF IA32_MTRRCAP.FIX is set AND range can be mapped using a
fixed-range MTRR
THEN
pre_mtrr_change();
update affected MTRR;
post_mtrr_change();
FI;
ELSE (* try to map using a variable MTRR pair *)
IF IA32_MTRRCAP.VCNT = 0
THEN return UNSUPPORTED;
FI;
IF conflicts with current variable ranges
THEN return RANGE_OVERLAP;
FI;
IF no MTRRs available
THEN return VAR_NOT_AVAILABLE;
FI;
IF BASE and SIZE do not meet the power of 2 requirements for
variable MTRRs
THEN return INVALID_VAR_REQUEST;
FI;
pre_mtrr_change();
Update affected MTRRs;
post_mtrr_change();
FI;