Tools: more info on debugging

Tools/debug/README.md

@@ -1,3 +1,94 @@
-This directory contains files that are useful for setting up to debug
-ArduPilot using either a black magic probe or a stlink-v2 with openocd
+# Hardware Debugging with ArduPilot
 
+This directory contains files that are useful for setting up to debug
+ArduPilot using either a black magic probe or a stlink-v2 with
+openocd.
+
+This assumes you are debugging a ChibiOS based firmware on a STM32 board.
+
+## Debugging with a Black Magic Probe
+
+If you have a black magic probe (see
+https://1bitsquared.com/products/black-magic-probe) then first make
+sure it has the latest firmware. See the wiki here for details:
+https://github.com/blacksphere/blackmagic/wiki
+
+Next, copy the file gdb-black-magic.init to the ArduPilot source
+directory, in the same directory where you will be starting the
+debugger. Rename the file to ".gdbinit"
+
+Now make sure you have the right version of arm-none-eabi-gdb
+installed. We recommend version 6-2017-q2-update, which is available
+here: http://firmware.ardupilot.org/Tools/STM32-tools/
+
+Now build ArduPilot with the --debug configure option. You may also
+like to include the --enable-asserts. Enabling asserts will slow down
+the firmware quite a lot, but will help catch ChibiOS API usage bugs.
+
+For example:
+
+  ./waf configure --board Pixhawk1 --debug --enable-asserts
+
+Now build and install your firmware:
+
+  ./waf copter --upload
+
+After it is loaded you can attach with gdb like this:
+
+ arm-none-eabi-gdb build/Pixhawk4/bin/arducopter
+
+then you can use normal gdb commands. If you are not familiar with gdb
+then do a google search.
+
+Note that for a source view the command "layout src" or "layout spit"
+is useful.
+
+## Debugging with a STLink-v2
+
+If you have a STLink-V2 adapter (or one of the very cheap clones) then
+you can debug with openocd. Using openocd has the advantage that you
+can debug threads properly, unlike the black magic probe which can't
+see ChibiOS threads.
+
+Start by installing the latest version of openocd, then copy the
+openocd.cfg file from this directory to the directory where you will
+be debugging.
+
+You may need to edit the openocd.cfg file to set the MCU type. The one
+in this directory is setup for a STM32F4 board. If you have a STM32F7
+or STM32H7 then edit the file in the obvious way.
+
+Now start openocd in a terminal. You should get output like this:
+
+```
+Open On-Chip Debugger 0.10.0+dev-00272-gedb6796 (2018-01-19-17:26)
+Licensed under GNU GPL v2
+For bug reports, read
+        http://openocd.org/doc/doxygen/bugs.html
+Info : auto-selecting first available session transport "hla_swd". To override use 'transport select <transport>'.
+Info : The selected transport took over low-level target control. The results might differ compared to plain JTAG/SWD
+adapter speed: 1800 kHz
+adapter_nsrst_delay: 100
+srst_only separate srst_nogate srst_open_drain connect_deassert_srst
+Info : clock speed 1800 kHz
+Info : STLINK v2 JTAG v29 API v2 SWIM v18 VID 0x0483 PID 0x374B
+Info : using stlink api v2
+Info : Target voltage: 3.253404
+Info : stm32h7x.cpu: hardware has 8 breakpoints, 4 watchpoints
+Info : Listening on port 3333 for gdb connections
+Info : Listening on port 6666 for tcl connections
+Info : Listening on port 4444 for telnet connections
+```
+
+the above output is for a STM32H743 Nucleo board, but others are
+similar
+
+In another terminal, copy the gdb-openocd.init file to the directory
+where you will be debugging, calling it .gdbinit.
+
+Now build and load the debug enabled firmware for ArduPilot in the
+same manner as given above for the Black Magic probe, and start
+arm-none-eabi-gdb in the same manner.
+
+To see ChibiOS threads use the "info threads" command. See the gdb
+documentation for more information.