
Chapter 11. Debug Support
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Real-Time Debug Support
11.6 Real-Time Debug Support
The ColdFire Family provides support debugging real-time applications. For these types
of embedded systems, the processor must continue to operate during debug. The
foundation of this area of debug support is that while the processor cannot be halted to
allow debugging, the system can generally tolerate the small intrusions of the BDM
inserting instructions into the pipeline with minimal effect on real-time operation.
The debug module provides three types of breakpoints: PC with mask, operand address
range, and data with mask. These breakpoints can be configured into one- or two-level
triggers with the exact trigger response also programmable. The debug module
programming model can be written from either the external development system using the
debug serial interface or from the processor’s supervisor programming model using the
WDEBUG instruction. Only CSR is readable using the external development system.
11.6.1 Theory of Operation
Breakpoint hardware can be configured through TDR[TCR] to respond to triggers by
displaying PSTDDATA, initiating a processor halt, or generating a debug interrupt. As
shown in Table 11-27, when a breakpoint is triggered, an indication (CSR[BSTAT]) is
provided on the PSTDDATA output port of the DDATA information when it is not
displaying captured processor status, operands, or branch addresses. See Section 11.3.2,
“Processor Stopped or Breakpoint State Change (PST = 0xE).”
The breakpoint status is also posted in CSR. Note that CSR[BSTAT] is cleared by a CSR
read when either a level-2 breakpoint is triggered or a level-1 breakpoint is triggered and a
level-2 breakpoint is not enabled. Status is also cleared by writing to either TDR or XTDR
to disable trigger options.
BDM instructions use the appropriate registers to load and configure breakpoints. As the
system operates, a breakpoint trigger generates the response defined in TDR.
PC breakpoints are treated in a precise manner: exception recognition and processing are
initiated before the excepting instruction is executed. All other breakpoint events are
recognized on the processor’s local bus, but are made pending to the processor and
Table 11-27. PSTDDATA Nibble/CSR[BSTAT] Breakpoint Response
PSTDDATA Nibble/CSR[BSTAT]
1
1
Encodings not shown are reserved for future use.
Breakpoint Status
0000/0000
No breakpoints enabled
0010/0001
Waiting for level-1 breakpoint
0100/0010
Level-1 breakpoint triggered
1010/0101
Waiting for level-2 breakpoint
1100/0110
Level-2 breakpoint triggered
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