NXP Semiconductors MC9S08LG16, Справочное руководство

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Chapter 19 Debug Module (DBG) (64K)
MC9S08LG32 MCU Series, Rev. 5
Freescale Semiconductor 367
correspond to separate instructions that could be propagating through the instruction queue at the same
time.
In end-type trace runs (BEGIN=0), when the comparator registers match, including the optional R/W
match, this signal goes to the CPU break logic where BRKEN determines whether a CPU break is
requested and the TAG control bit determines whether the CPU break will be a tag-type or force-type
breakpoint. When TRGSEL is set, the R/W qualified comparator match signal also passes through the
opcode tracking logic. If/when it propagates through this logic, it will cause a trigger to the ICE logic to
begin or end capturing information into the FIFO. In the case of an end-type (BEGIN=0) trace run, the
qualified comparator signal stops the FIFO from capturing any more information.
If a CPU breakpoint is also enabled, you would want TAG and TRGSEL to agree so that the CPU break
occurs at the same place in the application program as the FIFO stopped capturing information. If
TRGSEL was 0 and TAG was 1 in an end-type trace run, the FIFO would stop capturing as soon as the
comparator address matched, but the CPU would continue running until a TAG signal could propagate
through the CPUs instruction queue which could take a long time in the case where changes of flow caused
the instruction queue to be flushed. If TRGSEL was one and TAG was zero in an end-type trace run, the
CPU would break before the comparator match signal could propagate through the opcode tracking logic
to end the trace run.
In begin-type trace runs (BEGIN=1), the start of FIFO capturing is triggered by the qualified comparator
signals, and the CPU breakpoint (if enabled by BRKEN=1) is triggered when the FIFO becomes full. Since
this FIFO full condition does not correspond to the execution of a tagged instruction, it would not make
sense to use TAG=1 for a begin-type trace run.
19.4.4.1 Begin- and End-Trigger
The definition of begin- and end-trigger as used in the DBG module are as follows:
• Begin-trigger: Storage in FIFO occurs after the trigger and continues until 8 locations are filled.
• End-trigger: Storage in FIFO occurs until the trigger with the least recent data falling out of the
FIFO if more than 8 words are collected.
19.4.4.2 Arming the DBG Module
Arming occurs by enabling the DBG module by setting the DBGEN bit and by setting the ARM bit in the
DBGC register. The ARM bit in the DBGC register and the ARMF bit in the DBGS register are cleared
when the trigger condition is met in end-trigger mode or when the FIFO is filled in begin-trigger mode. In
the case of an end-trace where DBGEN=1 and BEGIN=0, ARM and ARMF are cleared by any reset to
end the trace run that was in progress. The ARMF bit is also cleared if ARM is written to zero or when the
DBGEN bit is low. The TBC logic determines whether a trigger condition has been met based on the
trigger mode and the trigger selection.
19.4.4.3 Trigger Modes
The on-chip ICE system supports nine trigger modes. The trigger modes are encoded as shown in
Table 19-16 . The trigger mode is used as a qualifier for either starting or ending the storing of data in the
FIFO. When the match condition is met, the appropriate flag AF or BF is set in DBGS register. Arming