
Chapter 11. Debug Support
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11-47
Background Debug Mode (BDM)
11.5.3.3.9 Synchronize PC to the PSTDDATA Lines (
SYNC
_
PC
)
The
SYNC
_
PC
command captures the current PC and displays it on the PSTDDATA
outputs. After the debug module receives the command, it sends a signal to the ColdFire
processor that the current PC must be displayed. The processor then forces an instruction
fetch at the next PC with the address being captured in the DDATA logic under control of
CSR[BTB]. The specific sequence of PSTDDATA values is as follows:
1. Debug signals a
SYNC
_
PC
command is pending.
2. CPU completes the current instruction.
3. CPU forces an instruction fetch to the next PC, generates a PST = 0x5 value
indicating a taken branch and signals the capture of DDATA.
4. The instruction address corresponding to the PC is captured.
5. The PST marker (0x9–0xB) is generated and displayed as defined by CSR[BTB]
followed by the captured PC address.
If the option to display ASID is enabled (CSR[3] = 1), the 8-bit ASID follows the address.
That is, the PSTDDATA sequence is {0x5, Marker, Instruction Address, 0x8, ASID},
where the 0x8 is the marker for the ASID.
The
SYNC
_
PC
command can be used to dynamically access the PC for performance
monitoring. The execution of this command is considerably less obtrusive to the real-time
operation of an application than a
HALT
-
CPU
/
READ
-
PC
/
RESUME
command sequence.
Command Formats:
Command Sequence:
Figure 11-39.
SYNC
_
PC
Command Sequence
Operand Data:
Result Data:
None
Command complete status (0xFFFF) is returned when the register
write is complete.
11.5.3.3.10 Force Transfer Acknowledge (
FORCE
_
TA
)
DEBUG_D logic implements the new
FORCE
_
TA
serial BDM command to resolve a hung
bus condition. In some system designs, references to certain unmapped memory addresses
may cause the external bus to hang with no transfer acknowledge generated by any bus
responders. The
FORCE
_
TA
forces generation of a transfer acknowledge signal, which can
15
12
11
8
7
4
3
0
0x0
0x0
0x0
0x1
Figure 11-38.
SYNC
_
PC
Command Format
NEXT CMD
"CMD COMPLETE"
SYNC_PC
F
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n
.