HOWTO
=====
-To run the gdb server, do (you do not need sudo if you have
-set up permissions correctly):
+First, load the sg kernel module.
+# modprobe sg
+
+To run the gdb server, do (you do not need sudo if you have set up
+permissions correctly):
$ make -C build && sudo ./build/st-util 1234 /dev/sg1
Then, in gdb:
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:1111
+Remote debugging using localhost:1111
+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 :1111' is good enough
+for GDB.
+
+Setting up udev rules
+=====================
+
+For convenience, you may install udev rules file, 10-stlink.rules, located
+in the root of repository. You will need to copy it to /etc/udev/rules.d,
+and then either reboot or execute
+$ udevadm control --reload-rules
+
+Udev will now create a /dev/stlink file, which will point at appropriate
+/dev/sgX device. Good to not accidentally start debugging your flash drive.
+
+Setting up modprobe rules
+=========================
+
+You may install a modprobe rules file, stlink.modprobe.conf, located in
+the root of the repository. You will need to copy it to /etc/modprobe.d
+and then
+ $ rmmod usb-storage
+If you have usb-storage built as a module, then this will cause it to be
+loaded with a "quirks" parameter that will cause it to ignore the STLink,
+rather than causing repeated errors and resets.
+
Running programs from SRAM
==========================
-You can run your firmware directly from SRAM if you want to.
-Just link it at 0x20000000 and do
+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
(gdb) load firmware.elf
then it would be written to the memory.
-Caveats
-=======
+FAQ
+===
+
+Q: My breakpoints do not work at all or only work once.
-GDB sends requests for a multi-sectioned ELF files (most ones;
-having both .text and .rodata is enough) in a quite strange way which
-absolutely does not conform to flash page boundaries. Which is even more
-weird when you think about FlashErase requests which it sends correctly.
-And I couldn't think of a way which will resolve this correctly now.
+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.
-Hardware breakpoints are not supported yet. You can still run your code from
-RAM, and then GDB will insert `bkpt' opcodes automagically.
+Q: At some point I use GDB command `next', and it hangs.
-Sometimes when you will try to use GDB `next' command to skip a loop,
+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'.