Sync inav to Gitea

docs/development/serial_printf_debugging.md

@@ -0,0 +1,152 @@
+# Serial printf style debugging
+
+## Overview
+
+INAV offers a function to use serial `printf` style debugging.
+
+This provides a simple and intuitive debugging facility.
+This facility is only available after the serial sub-system has been initialised, but logs generated prior to serial
+initialization can be obtained via the `bootlog` functionality.
+
+In order to use this feature, the source file must include `common/log.h`.
+
+## CLI settings
+
+It is necessary to set a serial port for serial logging using the function mask `FUNCTION_LOG`, 32768. For convenience this may be shared with MSP (mask 1), but no other function.
+For example, on a VCP port.
+
+```
+serial 20 32769 115200 115200 0 115200
+```
+
+If the port is shared, it will be reused with extant baud rate settings; if the port is not shared it is opened at 921600 baud.
+
+There are two run time settings that control the verbosity, the most verbose settings being:
+
+```
+log_level = DEBUG
+Allowed values: ERROR, WARNING, INFO, VERBOSE, DEBUG
+
+log_topics = 0
+Allowed range: 0 - 4294967295
+
+```
+
+The use of level and topics is described in the following sections.
+
+## LOG LEVELS
+
+Log levels are defined in `src/main/common/log.h`, at the time of writing these include (in ascending order):
+
+* LOG_LEVEL_ERROR
+* LOG_LEVEL_WARNING
+* LOG_LEVEL_INFO
+* LOG_LEVEL_VERBOSE
+* LOG_LEVEL_DEBUG
+
+These are used at both compile time and run time.
+
+At compile time, a maximum level may be defined. As of INAV 2.3, for F3 targets the maximum level is ERROR, for F4/F7 the maximum level is DEBUG.
+
+At run time, the level defines the level that will be displayed, so for a F4 or F7 target that has compile time suport for all log levels, if the CLI sets
+```
+log_level = INFO
+```
+then only `ERROR`, `WARNING` and `INFO` levels will be output.
+
+## Log Topic
+
+Log topics are defined in `src/main/common/log.h`, at the time of writing:
+
+* LOG_TOPIC_SYSTEM
+* LOG_TOPIC_GYRO
+* LOG_TOPIC_BARO
+* LOG_TOPIC_PITOT
+* LOG_TOPIC_PWM
+* LOG_TOPIC_TIMER
+* LOG_TOPIC_IMU
+* LOG_TOPIC_TEMPERATURE
+* LOG_TOPIC_POS_ESTIMATOR
+* LOG_TOPIC_VTX
+* LOG_TOPIC_OSD
+
+Topics are stored as masks (SYSTEM=1 ... OSD=1024) and may be used to unconditionally display log messages.
+
+If the CLI `log_topics` is non-zero, then all topics matching the mask will be displayed regardless of `log_level`. Setting `log_topics` to 4294967295 (all bits set) will display all log messages regardless of run time level (but still constrained by compile time settings), so F3 will still only display ERROR level messages.
+
+## Code usage
+
+A set of macros `LOG_ERROR()` (log error) through `LOG_DEBUG()` (log debug) may be used, subject to compile time log level constraints. These provide `printf` style logging for a given topic.
+
+Note that the `topic` is specified without the `LOG_TOPIC_` prefix:
+
+```
+//  LOG_DEBUG(topic, fmt, ...)
+LOG_DEBUG(SYSTEM, "This is %s topic debug message, value %d", "system", 42);
+```
+
+It is also possible to dump a hex representation of arbitrary  data, using functions named variously `LOG_BUFFER_` (`ERROR`) and `LOG_BUF_` (anything else, alas) e.g.:
+
+```
+// LOG_BUFFER_ERROR(topic, buf, size)
+// LOG_BUF_DEBUG(topic, buf, size)
+
+struct {...} tstruct;
+...
+LOG_BUF_DEBUG(TEMPERATURE, &tstruct, sizeof(tstruct));
+```
+
+## Output Support
+
+Log messages are transmitted through the `FUNCTION_LOG` serial port as MSP messages (`MSP_DEBUGMSG`). It is possible to use any serial terminal to display these messages, however it is advisable to use an application that understands `MSP_DEBUGMSG` in order to maintain readability (in a raw serial terminal the MSP message envelope may result in the display of strange characters). `MSP_DEBUGMSG` aware applications include:
+
+* [dbg-tool](https://codeberg.org/stronnag/dbg-tool)
+* [INAV Configurator](https://github.com/iNavFlight/inav-configurator)
+* [mwp](https://github.com/stronnag/mwptools)
+
+In addtion:
+
+* [msp-tool](https://github.com/fiam/msp-tool) is obsolete and has limited OS support.
+
+For example, with the final lines of `src/main/fc/fc_init.c` set to:
+
+```
+ LOG_ERROR(SYSTEM, "Init is complete");
+ systemState |= SYSTEM_STATE_READY;
+```
+
+and the following CLI settings:
+
+```
+serial 20 32769 115200 115200 0 115200
+set log_level = DEBUG
+set log_topics = 4294967295
+```
+
+The output will be formatted as follows:
+
+```
+# dbg-tool
+[dbg-tool] 12:46:49.909079 DBG: [     3.967] Init is complete
+
+# mwp (stderr log file)
+2020-02-02T19:09:02+0000 DEBUG:[     3.968] Init is complete
+
+# msp-tool
+[DEBUG] [     3.967] Init is complete
+```
+
+For the Configurator, debug messages are shown in the developer console log.
+
+Note: The numeric value in square brackets is the FC uptime in seconds.
+
+To see printf-style log messages generated prior serial initialization, reserve about 2KB RAM to buffer the
+log) by defining USE_BOOTLOG:
+#define USE_BOOTLOG 2048
+
+Then `make clean` and `make`.
+
+Then in the CLI you can run `bootlog` to see the buffered log.
+
+Note bootlog also requires that a serial port be defined for serial debugging.
+