
RCPU
REFERENCE MANUAL
DEVELOPMENT SUPPORT
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MOTOROLA
8-21
8.2.2.3 Ignore First Match
In order to facilitate the debugger utilities of “continue” and “go from x”, the option
to ignore the first match is supported for the I-bus breakpoints. When an I-bus
breakpoint is first enabled (as a result of the first write to the I-bus support control
register or as a result of the assertion of the MSR[RI] bit in masked mode), the first
instruction will not cause an I-bus breakpoint if the IFM (ignore first match) bit in the
I-bus support control register (ICTRL) is set (used for “continue”). This allows the
processor to be stopped at a breakpoint and then later to “continue” from that point
without the breakpoint immediately stopping the processor again before executing
the first instruction.
When the IFM bit is cleared, every matched instruction can cause an I-bus break-
point (used for “go from x,” where x is an address that would not cause a break-
point).
The IFM bit is set by the software and cleared by the hardware after the first I-bus
breakpoint match is ignored.
Since L-bus breakpoints are treated after the instruction is executed, L-bus break-
points and counter-generated I-bus breakpoints are not affected by this mode.
8.2.3 External Breakpoints
Breakpoints external to the processor can come from either an on-chip peripheral
or from the development port. For additional information on breakpoints from on-
chip peripherals, consult the user’s manual for the microcontroller of interest or the
reference manual for the peripheral of interest.
The development port serial interface can be used to assert either a maskable or
non-maskable breakpoint. Refer to
8.3.5 Trap-Enable Input Transmissions
for
more information about generating breakpoints from the development port. The de-
velopment port breakpoint bits remain asserted until they are cleared; however,
they cause a breakpoint only when they change from cleared to set. If they remain
set, they do not cause an additional breakpoint until they are cleared and set again.
External breakpoints are not referenced to any particular instruction; they are ref-
erenced to the current or following L-bus cycle. The breakpoint is taken as soon as
the processor completes an instruction that uses the L-bus.
8.2.4 Breakpoint Masking
The processor responds to two different types of breakpoints. The maskable
breakpoint is taken only if the processor is in a recoverable state. This means that
taking the breakpoint will not destroy any of the internal machine context. The pro-
cessor is defined to be in a recoverable state when the MSR[RI] (recoverable ex-
ception) bit is set. Maskable breakpoints are generated by the internal breakpoint
logic, modules on the IMB2, and the development port.
Non-maskable breakpoints cause the processor to stop without regard to the state
of the MSR[RI] bit. If the processor is in a non-recoverable state when the break-
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