Chapter 10. Memory Management Unit (MMU)
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10-7
Debugging in a Virtual Environment
The revised hit determination becomes the following:
ACRx_Hit = 0;
if (ACR
n
[10] == 1)
if ((address[31–24] == ACR
n
[31–24])) &&
((address[23–20] & ~ACR
n
[19–16]) == (ACR
n
[23–20] & ~ACR
n
[19–16])))
ACRx_Hit = 1;
elseif (address[31–24] & ~ACR
n
[23–16]) == (ACR
n
[31–24] & ~ACR
n
[23–16]))
ACRx_Hit = 1;
10.2.3.11 Supervisor Protection
Each K-Bus instruction or data reference is either a supervisor or user access. The CPU’s
status register supervisor bit (SR[S]) determines the operating mode. New ACR and CACR
bits protect supervisor space. See Table 10-1.
10.3 Debugging in a Virtual Environment
To support debugging in a virtual environment, numerous enhancements are implemented
in the ColdFire debug architecture. These enhancements are collectively called Debug
revision D and primarily relate to the addition of an 8-bit address space identifier (ASID)
to yield a 40-bit virtual address. This expansion affects two major debug functions:
The ASID is optionally included in the hardware breakpoint registers specification.
For example, the four PC breakpoint registers are expanded by 8 bits each, so that a
specific ASID value can be part of the breakpoint instruction address. Likewise, data
address/data breakpoint registers are expanded to include an ASID value. The new
control registers define whether and how the ASID is included in the breakpoint
comparison trigger logic.
The debug module implements the concept of ownership trace in which an ASID
value can be optionally displayed as part of real-time trace. When enabled, real-time
trace displays instruction addresses on any change-of-flow instruction that is not
absolute or PC-relative. For Debug revision D architecture, the address display is
expanded to optionally include ASID contents, thus providing the complete
instruction virtual address on these instructions. Additionally, when a Sync_PC
serial BDM command is loaded from the external development system, the
processor displays the complete virtual instruction address, including the 8-bit ASID
value.
The MMU control registers are accessible through serial BDM commands. See Chapter 11,
“Debug Support.”
10.4 Virtual Memory Architecture Processor Support
To support the MMU, enhancements have been made to the exception model, the stack
pointers, and the access error stack frame.
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n
.