PC912XDP512F0MPVR datasheet(773/1348 Pages) FREESCALE

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Chapter 20 S12X Debug (S12XDBGV3) Module

MC9S12XDP512 Data Sheet, Rev. 2.21

Freescale Semiconductor

775

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. If neither tracing nor breakpoints are enabled

then when the ﬁnal state is reached it returns automatically to state0 and the debug module is disarmed.

20.4.5

Trace Buffer Operation

The trace buffer is a 64 lines deep by 64-bits wide RAM array. The S12XDBG module stores trace

information in the RAM array in a circular buffer format. The S12XCPU 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 S12XCPU, 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 20-39. After each store the

counter register bits DBGCNT[6:0] are incremented. Tracing of S12XCPU activity is disabled when the

BDM is active but tracing of XGATE activity is still possible. Reading the trace buffer whilst the BDM is

active returns invalid data and the trace buffer pointer is not incremented.

20.4.5.1

Trace Trigger Alignment

Using the TALIGN bits (see Section 20.3.2.3”) 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. Using End or Mid-Trigger or when the

tracing is initiated by writing to the TRIG bit whilst conﬁgured for Begin-Trigger, tracing starts at the

second opcode after writing to DBGC1 if written in the CPU thread, .

20.4.5.1.1

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 S12XDBG 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.

20.4.5.1.2

Storing with Mid-Trigger

Storing with Mid-Trigger, data is stored in the Trace Buffer as soon as the S12XDBG 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 S12XDBG 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 is continued for another 32 lines. Upon tracing completion the

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

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