Freescale Semiconductor StarCore SC140 - Manual (Page 176)

4-66 SC140 DSP Core Reference Manual
Trace Unit Registers
In addition, the counter values could be added to the trace package of each trace event, thereby allowing to
monitor the elapsed cycles between trace events. The possible counter tracing modes are:
• TCOUNT upon a trace event, trace the counter value (ECNT_VAL)
• TCNTEXT upon a trace event, trace the extension counter value (ECNT_EXT).
This mode is usefull only with the TCOUNT mode.
Activating the TCOUNT mode adds a 32-bit entry to the traced package upon each trace event. Activating
the TCNTEXT mode in addition to the TCOUNT mode adds two 32-bit entries to the trace package upon
each trace event.
Both the counter modes cannot be activated with the TEXEC and TMARK mode, in order not to create
situations of tracing overflow.
The tracing mode combinations that are allowed are summarized in Table 4-22.
When the TB_CTRL register is configured for multiple trace data writes, there is a potential for data loss.
This is because each write to the trace buffer requires one core clock cycle. Requesting multiple trace
buffer actions such as setting TLOOP, TCOUNT and TCNEXT in TB_CTRL will require a core clock
cycle for each write - in this case, four clocks. If a long loop with only three execution sets is encountered
with the above TB_CTRL configuration, there are not enough cycles to write all the data. The value of the
extension counter register will be lost.
In TB_CTRL configurations where there are not enough core clock cycles to write all requested trace data,
the priority for writing data is as follows:
1. Destination and source address
2. Counter value
3. Extension counter value
When using the supported modes, source or destination addresses could not be lost.
When tracing in all modes except TMARK and TEXEC, the LSB of the PC of the source execution set is
always 1, while the LSB of all other words in a package is 0. This allows decoding the trace buffer contents
when the trace buffer is set to trace different cases, when all programmed information could not be written
to the trace buffer at the same time.
Table 4-22. Allowed tracing mode combinations
TCHOF TLOOP TINT TEXEC TMARK
TCOUNT or
TCOUNT & TCNTEXT
TCHOF + + - - +
TLOOP + + - - +
TINT + + - - +
TEXEC - - - - -
TMARK - - - - -
Allowed with
Trace mode