PC912XDP512F0MPVR datasheet(719/1348 Pages) FREESCALE

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Chapter 19 S12X Debug (S12XDBGV2) Module

MC9S12XDP512 Data Sheet, Rev. 2.21

Freescale Semiconductor

721

19.4.4.1

Final State

On entering ﬁnal state a trigger may be issued to the trace buffer according to the trace position control as

deﬁned by the TALIGN ﬁeld (see Section 19.3.1.3, “Debug Trace Control Register (DBGTCR)”). If the

TSOURCE bits in the trace control register DBGTCR are cleared then the trace buffer is disabled and the

transition to ﬁnal state can only generate a breakpoint request. In this case or upon completion of a tracing

session when tracing is enabled, the ARM bit in the DBGC1 register is cleared, returning the module to

the disarmed state0. If tracing is enabled a breakpoint request can occur at the end of the tracing session.

19.4.5

Trace Buffer Operation

The trace buffer is a 64 lines deep by 64-bits wide RAM array. The DBG module stores trace information

in the RAM array in a circular buffer format. The CPU accesses the RAM array through a register window

(DBGTBH:DBGTBL) using 16-bit wide word accesses. After each complete 64-bit trace buffer line is

read via the CPU, an internal pointer into the RAM is incremented so that the next read will receive fresh

information. Data is stored in the format shown in Table 19-39. After each store the counter register bits

DBGCNT[6:0] are incremented. Tracing of CPU activity is disabled when the BDM is active but tracing

of XGATE activity is still possible. Reading the trace buffer while the BDM is active returns invalid data

and the trace buffer pointer is not incremented.

19.4.5.1

Trace Trigger Alignment

Using the TALIGN bits (see Section 19.3.1.3, “Debug Trace Control Register (DBGTCR)”) it is possible

to align the trigger with the end, the middle or the beginning of a tracing session.

If end or mid tracing is selected, tracing begins when the ARM bit in DBGC1 is set and State1 is entered.

The transition to ﬁnal state if end is selected signals the end of the tracing session. The transition to ﬁnal

state if mid is selected signals that another 32 lines will be traced before ending the tracing session. Tracing

with begin-trigger starts at the opcode of the trigger.

19.4.5.1.1

Storing with Begin-Trigger

Storing with begin-trigger, data is not stored in the trace buffer until the ﬁnal state is entered. Once the

trigger condition is met the DBG module will remain armed until 64 lines are stored in the trace buffer. If

the trigger is at the address of the change-of-ﬂow instruction the change of ﬂow associated with the trigger

will be stored in the trace buffer. Using begin-trigger together with tagging, if the tagged instruction is

about to be executed then the trace is started. Upon completion of the tracing session the breakpoint is

generated, thus the breakpoint does not occur at the tagged instruction boundary.

19.4.5.1.2

Storing with Mid-Trigger

Storing with mid-trigger, data is stored in the trace buffer as soon as the DBG module is armed. When the

trigger condition is met, another 32 lines will be traced before ending the tracing session, irrespective of

the number of lines stored before the trigger occurred, then the DBG module is disarmed and no more data

is stored. If the trigger is at the address of a change of ﬂow instruction the trigger event is not stored in the

trace buffer. Using mid-trigger with tagging, if the tagged instruction is about to be executed then the trace

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