Introduction
============

This is a fork of https://github.com/texane/stlink . Unless you happen
to have the exact same set of requirements as I do the trade-offs here
are probably not going to work for you, so please just use the
original.

After hitting some hard to debug errors I've gone through and added
extensive error checking throughout so that there are much fewer silent
errors than previously. It is important to note that most of the causes
of these silent errors are due to the code being debugged, rather than
any fundamental problems in stlink; so please, just use the original!

The rest of the changes I have made are mostly for my own taste and
environment, so again, please use the original.

Currently this is only tested on OS X, with the STM32F4 discovery board.
There is no support for STLINKv1.

Additionally, I'm only really interested in the gdbserver portion of the
project so, anything else has more or less been stripped away.

In terms of feature set, there are some significant improvements. Firstly
the gdbserver is persistent, which means that you can exit from gdb, and
then later reattach with a new instance of gdb.

Secondly, it is possible to attach and detach from the running system
from within gdb.

HOWTO
=====

First, you have to know there are several boards supported by the software.
Those boards use a chip to translate from USB to JTAG commands. The chip is
called stlink and there are 2 versions:
. STLINKv1, present on STM32VL discovery kits,
. STLINKv2, present on STM32L discovery and later kits.

Only the STLINKv2 protocol is supported.

Common requirements
~~~~~~~~~~~~~~~~~~~

. libusb-1.0  (You probably already have this, but you'll need the
development version to compile)

COMPILING
~~~~~~~~~

$ make

USING THE GDBSERVER
~~~~~~~~~~~~~~~~~~~
To run the gdb server: (you do not need sudo if you have set up
permissions correctly)

$ make && [sudo] ./st-util

There are a few options:

./st-util - usage:

  -h, --help        Print this help
  -vXX, --verbose=XX    specify a specific verbosity level (0..99)
  -v, --verbose specify generally verbose logging
  -p 4242, --listen_port=1234
            Set the gdb server listen port. (default port: 4242)

Then, in your project directory, someting like this...
(remember, you need to run an _ARM_ gdb, not an x86 gdb)

$ arm-none-eabi-gdb fancyblink.elf
...
(gdb) tar extended-remote :4242
...
(gdb) load
Loading section .text, size 0x458 lma 0x8000000
Loading section .data, size 0x8 lma 0x8000458
Start address 0x80001c1, load size 1120
Transfer rate: 1 KB/sec, 560 bytes/write.
(gdb)
...
(gdb) run

Have fun!

Resetting the chip from GDB
===========================

You may reset the chip using GDB if you want. You'll need to use `target
extended-remote' command like in this session:
(gdb) target extended-remote localhost:4242
Remote debugging using localhost:4242
0x080007a8 in _startup ()
(gdb) kill
Kill the program being debugged? (y or n) y
(gdb) run
Starting program: /home/whitequark/ST/apps/bally/firmware.elf

Remember that you can shorten the commands. `tar ext :4242' is good enough
for GDB.

Running programs from SRAM
==========================

You can run your firmware directly from SRAM if you want to. Just link
it at 0x20000000 and do
(gdb) load firmware.elf

It will be loaded, and pc will be adjusted to point to start of the
code, if it is linked correctly (i.e. ELF has correct entry point).

Writing to flash
================

The GDB stub ships with a correct memory map, including the flash area.
If you would link your executable to 0x08000000 and then do
(gdb) load firmware.elf
then it would be written to the memory.

FAQ
===

Q: My breakpoints do not work at all or only work once.

A: Optimizations can cause severe instruction reordering. For example,
if you are doing something like `REG = 0x100;' in a loop, the code may
be split into two parts: loading 0x100 into some intermediate register
and moving that value to REG. When you set up a breakpoint, GDB will
hook to the first instruction, which may be called only once if there are
enough unused registers. In my experience, -O3 causes that frequently.

Q: At some point I use GDB command `next', and it hangs.

A: Sometimes when you will try to use GDB `next' command to skip a loop,
it will use a rather inefficient single-stepping way of doing that.
Set up a breakpoint manually in that case and do `continue'.

Currently known working combinations of programmer and target
=============================================================

STLink v2 (as found on the 32L and F4 Discovery boards)
Known Working Targets:
* STM32F407xx (STM32F4 Discovery board)

Please report any and all known working combinations so I can update this!