Traces

A FW developer may log important events by adding trace_event(...) entries to the source code. The data is collected in the internal buffer and transmitted periodically to the host through the DMA.

Building & Processing Traces

During the compilation and linking, string literals and log entry metadata is linked to the special debug sections that are extracted later to a special dictionary file. This part is not loaded to the DSP and does not occupy the DSP memory keeping both the memory footprint and the trace DMA payload small.

digraph build_proc_traces { node [shape = record]; rankdir = LR; src [label = "source files\n \{ trace_event(...) \}"]; elf [label = "ELF|<text>.text|<data>.data|<others>...\n\n |<sle>.static_log_entries"]; /* compilation & linking */ src -> elf; src -> elf:sle [style = dotted, label = "trace\nevent\ndata"] /* make bin -> rimage */ ri [label = "sof- .ri"]; elf:text -> ri; elf:data -> ri; elf:others -> ri; elf:sle -> lcd_file [style = dotted]; }

Figure 57 Traces - build process

Once the binary trace data is received by the host driver, it is accessible to the trace decoder (logger) through the files located in the _/sys/kernel/debug/sof/…_. The logger requires the dictionary file to decode the trace data and “printf” them using format specified in the source files.

digraph build_proc_traces { node [shape = record]; rankdir = LR; ri [label = "sof- .ri"]; lcd_file; dsp [label = "FW\n@ DSP ", style = filled, color = "#92d050"]; ri -> dsp drv [label = "Driver\n@ host", style = filled, color = "#92d050"] dsp -> drv [style = dashed, label = "<<dma>>\ntraces..."]; log [label = "/sys/..."]; drv -> log [style = dashed]; log -> logger [style = dashed]; lcd_file -> logger [style = dotted]; logger -> tty [label = "pretty\nprinted\ntraces"]; { rank = same; ri; lcd_file } }

Figure 58 Traces - running & processing

Enabling Traces

When the traces are enabled by the driver, it stores the FW version information received along with the FW Ready IPC message at the beginning of the local trace files. It enables simple compatibility check between the trace data and the dictionary file performed by the logger.

Note that the trace data may be collected on some machine and sent along with the dictionary file to another person for investigation. It is important to be able to verify the consistency of both by having the build version attached to them.

participant "Driver" as drv
participant "FW" as fw

drv <- fw : <<IPC>> fw ready (fw_version)
   activate drv
drv -> drv : remember fw_version
   activate drv
   deactivate drv
deactivate drv

...

drv -> fw : <<IPC>> dma trace enable

Adding Traces

Refer to the src/include/sof/trace.h.