OpenOCD

September 20, 2016

Amazingly, this is available as a fedora package, so I just do:

dnf install openocd
Installing:
 hidapi                                     x86_64                     0.8.0-0.2.d17db57.fc24
 libftdi                                    x86_64                     1.2-8.fc24
 openocd                                    x86_64                     0.9.0-4.fc24
After doing this, I set up an "ocd" script with the following:
openocd -f /usr/share/openocd/scripts/interface/stlink-v2.cfg -f /usr/share/openocd/scripts/target/stm32f1x.cfg
I put this script into /home/tom/bin so I can start openOCD without having to remember impossible long things. There is a nice 172 page PDF user manual for OpenOCD.

What about gdb?

On my fedora system, the available gcc and gdb packages look like so:
arm-none-eabi-gdb.x86_64                 7.6.2-4.fc24                   fedora  
arm-none-eabi-gcc-cs.x86_64              1:5.2.0-4.fc24                 fedora  
gcc-arm-linux-gnu.x86_64                 6.1.1-2.fc24                   updates 
So, I have two gcc choices and only one gdb choice. I wonder if that gdb will work with the gcc-arm-linux compiler I am using? Nothing like just diving in, so I install it and:
dnf install arm-none-eabi-gdb

ocd &
make gdb
arm-none-eabi-gdb --eval-command="target remote localhost:3333" blink.elf
GNU gdb (GDB) 7.6.2
Copyright (C) 2013 Free Software Foundation, Inc.
This GDB was configured as "--host=x86_64-unknown-linux-gnu --target=arm-none-eabi".
Reading symbols from /u1/Projects/STM32/Archive/blink1/blink.elf...(no debugging symbols found)...done.
Remote debugging using localhost:3333
0x00000000 in ?? ()
Note that I put the jive to start gdb into my makefile.

I find it useful to keep at least 3 windows open. One running OpenOCD, the other with a telnet to port 4444 to send commands directly to openocd, and another running gdb via port 3333. Maybe a fourth with vim showing the source code.

Also if you want to enjoy debuggine with gdb, compile with the -g flag.
And, if you forget the elf file at the end of the gdb line use "file blink.elf" to get the debug information.

gdbtui

Something called "gdbtui" is "text user interface", which is a text user interface on top of gdb. I was going to give up because there is no gdbtui package as such available on Fedora. But, it turns out you can get this via "gdb -tui" if you want to play with it. Alternately you can press C-x C-a after starting gdb. So it is a standard part of gdb, and pretty doggone nice.

Enter "layout asm" to make the upper window display assembly -- this will automatically follow your instruction pointer, although you can also change frames or scroll around while debugging. Press C-x s to enter SingleKey mode, where "run continue up down finish" etc. are abbreviated to a single key. This allows you to move quicky through your program.

s = step
n = next
c = continue
r = run
f = finish
d = down
u = up
w = where
v = info locals

Useful gdb commands

It isn't a gdb command, but just for the record, the openocd command to place an image in flash is:
flash write_image erase blink.bin 0x08000000
Note that for this to work, openocd itself must have been started in the same directory that contains the image.
i r -- shows the registers
stepi -- execute one assembly instruction
nexti -- as above, but a function call is executed until it returns
disas 0x50, 0x60 - disassemble from start to end
x/nfu 0x40 - examines memory
    n = how many
    f = format (usually x for hex), maybe x, i, s
    u = how big b, h, w, g are 1,2,4,8 byte objects
continue -- run to breakpoint (or forever)
    note that "reset halt" in openocd window will get control

Random stuff and possibly useful links


Feedback? Questions? Drop me a line!

Tom's Computer Info / tom@mmto.org