System Control
ARM DDI 0500D
Copyright © 2013-2014 ARM. All rights reserved.
4-229
ID021414
Non-Confidential
Write access to the Secure copy of TTBCR is disabled if the
CP15SDISABLE
signal is asserted HIGH.
Attributes
TTBCR is a 32-bit register.
There are two formats for this register. TTBCR.EAE determines which format of the register is
used. This section describes:
•
TTBCR format when using the Short-descriptor translation table format
.
•
TTBCR format when using the Long-descriptor translation table format
.
TTBCR format when using the Short-descriptor translation table format
Figure 4-115
shows the TTBCR bit assignments when TTBCR.EAE is 0.
Figure 4-115 TTBCR bit assignments, TTBCR.EAE is 0
Table 4-210
shows the TTBCR bit assignments when TTBCR.EAE is 0.
TTBCR format when using the Long-descriptor translation table format
Figure 4-116 on page 4-230
shows the TTBCR bit assignments when TTBCR.EAE is 1.
31 30
6 5 4 3 2
0
N
RES
0
PD1
EAE
PD0
RES
0
Table 4-210 TTBCR bit assignments, TTBCR.EAE is 0
Bits
Name
Function
[31]
EAE
Extended Address Enable.
0
Use the 32-bit translation system, with the Short-descriptor translation table format.
[30:6]
-
Reserved,
RES
0.
[5]
PD1
Translation table walk disable for translations using TTBR1. This bit controls whether a translation table walk is
performed on a TLB miss, for an address that is translated using TTBR1. The possible values are:
0
Perform translation table walks using TTBR1.
1
A TLB miss on an address that is translated using TTBR1 generates a Translation fault. No
translation table walk is performed.
[4]
PD0
Translation table walk disable for translations using TTBR0. This bit controls whether a translation table walk is
performed on a TLB miss for an address that is translated using TTBR0. The possible values are:
0
Perform translation table walks using TTBR0.
1
A TLB miss on an address that is translated using TTBR0 generates a Translation fault. No
translation table walk is performed.
[3]
-
Reserved,
RES
0.
[2:0]
N
Indicate the width of the base address held in TTBR0. In TTBR0, the base address field is bits[31:14-N]. The value
of N also determines:
•
Whether TTBR0 or TTBR1 is used as the base address for translation table walks.
•
The size of the translation table pointed to by TTBR0.
N can take any value from 0 to 7, that is, from 0b000 to 0b111.
When N has its reset value of 0, the translation table base is compatible with ARMv5 and ARMv6.
Resets to 0.