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Debug Module
34-51
Freescale Semiconductor
Refer to the
ColdFire Programmer’s Reference Manual
. for more information.
In the case of a two-level trigger, the last breakpoint event determines the exception vector; however, if
the second-level trigger is PC || Address {&& Data} (as shown in the last condition in the code example
in
Section 34.3.11.1, “Resulting Set of Possible Trigger Combinations
”), the vector taken is determined by
the first condition that occurs after the first-level trigger: vector 13 if PC occurs first or vector 12 if Address
{&& Data} occurs first. If both occur simultaneously, the non-PC-breakpoint debug interrupt is taken
(vector number 12).
Execution continues at the instruction address in the vector corresponding to the debug interrupt. The
debug interrupt handler can use supervisor instructions to save the necessary context, such as the state of
all program-visible registers into a reserved memory area.
During a debug interrupt service routine, all normal interrupt requests are evaluated and sampled once per
instruction. If any exception occurs, the processor responds as follows:
1. It saves a copy of the current value of the emulator mode state bit and then exits emulator mode by
clearing the actual state.
2. The fault status field (FS) in the next exception stack frame is set to 0010 to indicate the processor
was in emulator mode when the interrupt occurred. See
Section 3.3.3.1, “Exception Stack Frame
3. It passes control to the appropriate exception handler.
4. It executes an RTE instruction when the exception handler finishes. During the processing of the
RTE, FS is reloaded from the system stack. If this bit field is set to 0010, the processor sets the
emulator mode state and resumes execution of the original debug interrupt service routine. This is
signaled externally by the generation of the PST value that originally identified the debug interrupt
exception, that is, PST = 0xD.
Fault status encodings are listed in
. The implementation of this debug interrupt handling fully
supports the servicing of a number of normal interrupt requests during a debug interrupt service routine.
The emulator mode state bit is essentially changed to be a program-visible value, stored into memory
during exception stack frame creation, and loaded from memory by the RTE instruction.
When debug interrupt operations complete, the RTE instruction executes and the processor exits emulator
mode. After the debug interrupt handler completes execution, the external development system can use
BDM commands to read the reserved memory locations.
In revisions B/B+ and C, the hardware inhibits generation of another debug interrupt during the first
instruction after the RTE exits emulator mode. This behavior is consistent with the logic involving trace
mode where the first instruction executes before another trace exception is generated. Thus, all hardware
breakpoints are disabled until the first instruction after the RTE completes execution, regardless of the
programmed trigger response.
34.4.2.2
Emulator Mode
Emulator mode facilitates non-intrusive emulator functionality. This mode can be entered in three different
ways:
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