ARM Architecture Reference Manual ARMv7-A and ARMv7-R edition

Virtual Memory System Architecture (VMSA)
Four bits in the PRRR permit mapping of the Shareable attribute by defining, for the translation table
S bit:
— the meaning of S == 0 if the region is identified as Device memory
— the meaning of S == 1 if the region is identified as Device memory
— the meaning of S == 0 if the region is identified as Normal memory
— the meaning of S == 1 if the region is identified as Normal memory.
In each case, the meaning of the Shareable bit value is that the memory region is one of:
— Shareable
— Non-shareable.
For each of the possible encodings of the TEX[0], C and B bits in a translation table entry, Table B3-9 shows
which fields of the PRRR and NMRR registers describe the memory region attributes.
To find the meaning of the value of the S bit in a translation table entry you must:
use Table B3-9 to find the memory type of the region described by the entry
if the memory type is Strongly-ordered then the region is Shareable
Table B3-9 TEX, C, and B encodings when TRE == 1
Encoding
Memory typea Cache attributesa, b :
TEX[0] C B Inner cache Outer cache
Outer Shareable
attribute b
0 0 0 PRRR[1:0] NMRR[1:0] NMRR[17:16] NOT(PRRR[24])
0 0 1 PRRR[3:2] NMRR[3:2] NMRR[19:18] NOT(PRRR[25])
0 1 0 PRRR[5:4] NMRR[5:4] NMRR[21:20] NOT(PRRR[26])
0 1 1 PRRR[7:6] NMRR[7:6] NMRR[23:22] NOT(PRRR[27])
1 0 0 PRRR[9:8] NMRR[9:8] NMRR[25:24] NOT(PRRR[28])
1 0 1 PRRR[11:10] NMRR[11:10] NMRR[27:26] NOT(PRRR[29])
1 1 0 IMPLEMENTATION
DEFINED
IMPLEMENTATION
DEFINED
IMPLEMENTATION
DEFINED
IMPLEMENTATION
DEFINED
1 1 1 PRRR[15:14] NMRR[15:14] NMRR[31:30] NOT(PRRR[31])
a. For details of the memory type field encodings see c10, Primary Region Remap Register (PRRR) on page B3-143. For
details of the cache attribute encodings see Table B3-8 on page B3-34.
b. Only applies if the memory type for the region is mapped as Normal memory and the location is Shareable.
if the memory type is not Strongly-ordered then look up the memory type and value of the S bit in
Table B3-10 on page B3-36 to find which bit of the PRRR defines the Shareable attribute of the
region.
ARM DDI 0406B Copyright © 1996-1998, 2000, 2004-2008 ARM Limited. All rights reserved. B3-35