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ColdFire CF4e Core User’s Manual
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Motorola-Recommended BDM Pinout
As part of the Rev. C functionality, the operation of the debug interrupt is modified in the
following manner:
1. The occurrence of the breakpoint trigger, configured to generate a debug interrupt,
is treated exactly as before. The debug interrupt is treated as a higher priority
exception relative to the normal interrupt requests encoded on the interrupt priority
input signals.
2. At the appropriate sample point, the ColdFire processor initiates debug interrupt
exception processing. This event is signaled externally by the generation of a
unique PST value (PST = 0xD) asserted for multiple cycles. The processor sets the
emulator mode state bit as part of this exception processing.
3. While the processor in the debug interrupt service routine, all normal interrupt
requests are evaluated and sampled once per instruction. While in this routine, if
any type of exception occurs, the processor responds in the following manner:
a) In response to the new exception, the processor saves a copy of the current value
of the emulator mode state bit and then exits emulator mode by clearing the
actual state.
b) The new exception stack frame sets bit 1 of the fault status field, using the saved
emulator mode bit, indicating execution while in emulator mode has been
interrupted. This corresponds to bit 17 of the longword at the top of the system
stack.
c) Control is passed to the appropriate exception handler.
d) When the exception handler is complete, a Return From Exception (RTE)
instruction is executed. During the processing of the RTE, FS[1] is reloaded
from the system stack. If this bit is asserted, 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 occurrence of a debug interrupt exception, that is, PST
= 0xD.
Implementation of this revised debug interrupt handling fully supports the servicing of any
number of normal interrupt requests while in 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.
11.9 Motorola-Recommended BDM Pinout
The ColdFire BDM connector, Figure 11-1, is a 26-pin Berg connector arranged 2 x 13.
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