
10-6
ColdFire CF4E Core User’s Manual
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Virtual Memory Management Architecture
Data write
See Section 10.4.3, “Access Error Stack Frame Additions,” for more information.
10.2.3.8 Expanded Control Register Space
MMUBAR is added for ColdFire virtual mode. Like other control registers, it can be
accessed from the debug module or written using the privileged MOVEC instruction. See
Chapter 2, “Registers.”
10.2.3.9 Changes to ACRs and CACR
New ACR and CACR bits, Table 10-1, improve address granularity and supervisor mode
protection. These improvements are not necessary to implement the ColdFire MMU but
they improve K-Bus memory functionality for physical and virtual address environments.
10.2.3.10 ACR Address Improvements
ACRs provide a 16-Mbyte address window. For a given request address, if the ACR is valid
and the request mode matches the mode specified in the supervisor mode field, ACR
n
[S],
hit determination is specified as follows:
ACRx_Hit = 0;
if ((address[31:24] & ~ACR
n
[23:16]) == (ACR
n
[31:24] & ~ACR
n
[23:16]))
ACRx_Hit = 1;
With this hit function, ACRs can assign address attributes for user or supervisor requests to
memory spaces of at least 16 MBytes (through the address mask). With the MMU
definition, the ACR hit function is improved by the address mask mode bit (ACR
n
[AMM]),
which supports finer address granularity. See Table 10-1.
Table 10-1. New ACR and CACR Bits
Bits
Name
Description
ACR
n
[10]
AMM
Address mask mode. Determines access to the associated address space.
0 The ACR hit function is the same as previous versions, allowing control of a 16-Mbyte or
greater memory region.
1 The upper 8 bits of the address and ACR are compared without a mask function; bits 23–20
of the address and ACR are compared masked by ACR[19–16], allowing control of a 1- to
16-Mbyte region.
Reset value is 0.
ACR
n
[3]
SP
Supervisor protect. Determines access to the associated address space.
0 Supervisor and user access allowed.
1 Only supervisor access allowed. Attempted user access causes an access error exception.
Reset value is 0.
CACR[23]
DDSP
Default data supervisor protect. Determines access to the associated data space.
0 Supervisor and user access allowed.
1 Only supervisor access allowed. Attempted user access causes an access error exception.
Reset value is 0.
CACR[7]
DISP
Default instruction supervisor protect. Determines access to the associated instruction space.
0 Supervisor and user access allowed.
1 Only supervisor access allowed. Attempted user access causes access error exception
Reset value is 0.
F
Freescale Semiconductor, Inc.
n
.