Chapter 4. API Guides
Fig. 1: Tracing Components when Working Over JTAG
4.1.3 Configuration Options and Dependencies
Using of this feature depends on two components:
1. Host side: Application tracing is done over JTAG, so it needs OpenOCD to be set up and running on host
machine. For instructions on how to set it up, please see JTAG Debugging for details.
2. Target side: Application tracing functionality can be enabled in menuconfig. Component config > Application
Level Tracing menu allows selecting destination for the trace data (HW interface for transport). Choosing any
of the destinations automatically enables CONFIG_APPTRACE_ENABLE option.
Note: In order to achieve higher data rates and minimize number of dropped packets it is recommended to optimize
setting of JTAG clock frequency, so it is at maximum and still provides stable operation of JTAG, see Optimize JTAG
speed.
There are two additional menuconfig options not mentioned above:
1. Threshold for flushing last trace data to host on panic (CONFIG_APPTRACE_POSTMORTEM_FLUSH_THRESH).
This option is necessary due to the nature of working over JTAG. In that mode trace data are exposed to the
host in 16 KB blocks. In post-mortem mode when one block is filled it is exposed to the host and the previous
one becomes unavailable. In other words trace data are overwritten in 16 KB granularity. On panic the latest
data from the current input block are exposed to host and host can read them for post-analysis. System panic
may occur when very small amount of data are not exposed to the host yet. In this case the previous 16 KB of
collected data will be lost and host will see the latest, but very small piece of the trace. It can be insufficient
to diagnose the problem. This menuconfig option allows avoiding such situations. It controls the threshold
for flushing data in case of panic. For example user can decide that it needs not less then 512 bytes of the
recent trace data, so if there is less then 512 bytes of pending data at the moment of panic they will not be
flushed and will not overwrite previous 16 KB. The option is only meaningful in post-mortem mode and when
working over JTAG.
2. Timeout for flushing last trace data to host on panic (CONFIG_APPTRACE_ONPANIC_HOST_FLUSH_TMO).
The option is only meaningful in streaming mode and controls the maximum time tracing module will wait for
the host to read the last data in case of panic.
Espressif Systems 1254
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