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README.md

PyCortexMDebug

A set of GDB/Python-based utilities to make life debugging ARM Cortex-M processors a bit easier

It will consist of several modules which will hopefully become integrated as they evolve. Presently, there is only one:

SVD

ARM defines an SVD (System View Description) file format in its CMSIS standard as a means for Cortex-M-based chip manufacturers to provide a common description of peripherals, registers, and register fields. You can download SVD files for different manufacturers here.

My implementation so far has only tested STM32 chips but should hold for others. If others are like those from ST, expect plenty of errors in the file. Like GPIOA having a register named GPIOB_OSPEEDR and lots of 16-bit registers that are listed as 32!

The implementation consists of two components -- An lxml-based parser module (pysvd) and a GDB file (gdb_svd). I haven't yet worked out a perfect workflow for this, though it's quite easy to use when you already tend to have a GDB initialization file for starting up OpenOCD and the like. However your workflow works, just make sure to, in GDB:

source gdb_svd.py
svd_load [your_svd_file].svd

These files can be huge so it might take a second or two. Anyways, after that, you can do

svd

to list available peripherals with descriptions. Or you can do

svd [some_peripheral_name]

to see all of the registers (with their values) for a given peripheral. For more details, run

svd [some_peripheral_name] [some_register_name]

to see all of the field values with descriptions.

You can add format modifiers like:

  • svd/x will display values in hex
  • svd/o will display values in octal
  • svd/t or svd/b will display values in binary
  • svd/a will display values in hex and try to resolve symbols from the values

All field values are displayed at the correct lengths as provided by the SVD files. Also, tab completion exists for nearly everything! When in doubt, run svd help.

TODO

Enable writing to registers and individual fields

Bugs

There are probably a few. All planning, writing, and testing of this was done in an afternoon. There may be some oddities in working with non-STM32 parts. I'll play with this when I start working with other controllers again. If something's giving you trouble, describe the problem and it shall be fixed.

DWT

The ARM Data Watchpoint and Trace Unit (DWT) offers data watchpoints and a series of gated cycle counters. For now, I only support the raw cycle counter but facilities are in place to make use of others. As this is independent of the specific device under test, commands are simple and you can configure a clock speed to get real time values from counters.

dwt configclk 48000000

will set the current core clock speed. Then

dwt cyccnt reset
dwt cyccnt enable

will reset and start the cycle counter. At any point

dwt cycnt

will then indicate the number of cycles and amount of time that has passed.

ITM/ETM support

This is not implemented yet. I want to have more complete support for some of the nicer debug and trace features on Cortex-M processors. Parts of this will probably be dependent on OpenOCD and possibly on specific interfaces. I'll try to avoid this where possible but can't make any promises.