Intel ARCHITECTURE IA-32 User Manual download pdf (Page 477)

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Vol. 3A 10-37

MEMORY CACHE CONTROL

The pseudocode for the Get4KMemType() function in Example 10-17 obtains the memory type

for a single 4-KByte range at a given physical address. The sample code determines whether an

PHY_ADDRESS falls within a fixed range by comparing the address with the known fixed

ranges: 0 to 7FFFFH (64-KByte regions), 80000H to BFFFFH (16-KByte regions), and C0000H

to FFFFFH (4-KByte regions). If an address falls within one of these ranges, the appropriate bits

within one of its MTRRs determine the memory type.

Example 10-17. Get4KMemType() Pseudocode

IF IA32_MTRRCAP.FIX AND MTRRdefType.FE /* fixed registers enabled */

THEN IF PHY_ADDRESS is within a fixed range

return IA32_MTRR_FIX.Type;

FI;

FOR each variable-range MTRR in IA32_MTRRCAP.VCNT

IF IA32_MTRR_PHYSMASK.V = 0

THEN continue;

FI;

IF (PHY_ADDRESS AND IA32_MTRR_PHYSMASK.Mask) =

(IA32_MTRR_PHYSBASE.Base

AND IA32_MTRR_PHYSMASK.Mask)

THEN

return IA32_MTRR_PHYSBASE.Type;

FI;

ROF;

return MTRRdefType.Type;

10.11.7.2 MemTypeSet() Function

The MemTypeSet() function in Example 10-18 sets a MTRR for the physical memory range

specified by the parameters base and size to the type specified by type. The base address and

size are multiples of 4 KBytes and the size is not 0.

Example 10-18. 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;

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