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pycs

Free

Python Based ARM CoreSight Debug and Trace Tools

FreeFree tier
Type
Open Source
Visit Website GitHub (40 stars)

About pycs

PyCS is an open-source Python-based JTAG/SWD debugger for ARM Cortex-M microcontrollers. It reads SoC SVD (System View Description) files to provide full peripheral and register decodes for a wide variety of Cortex-M based chips, including STM32, nRF, EFM32, and Atmel SAM series. The tool features an interactive command-line interface with command completion, memory display and disassembly, CPU halt/go, flash programming, a Segger RTT client, and counter frequency measurement. It supports multiple debug interfaces such as ST-Link, J-Link, and CMSIS-DAP. PyCS is licensed under the MIT license and requires Python3 with dependencies like python3-lxml and python3-hid.

Key Features

JTAG/SWD debug interface support for ARM Cortex-M microcontrollers
Reads SoC SVD (System View Description) files for full peripheral and register decodes
Interactive command-line interface (CLI) with tab completion and help
Memory display and disassembly (ARM Thumb/Thumb-2)
CPU halt/go and single-step control
Flash programming capability
Segger RTT (Real-Time Transfer) client support
Counter frequency measurement
Support for multiple debug probes (ST-Link, J-Link, CMSIS-DAP)
Supports a wide variety of target devices (STM32, nRF, EFM32, Atmel SAM, etc.)

Pros & Cons

Pros
  • Free and open source (MIT license) with no proprietary software requirements
  • Reads SVD files for detailed register-level debugging without manual lookup
  • Supports a wide range of common Cortex-M development boards and chips
  • Interactive CLI with command completion and help makes it user-friendly
  • Works with popular and affordable debug probes (ST-Link, J-Link, CMSIS-DAP)
  • Active development on GitHub with community contributions
Cons
  • Requires Python3 and additional system packages (python3-lxml, python3-hid)
  • Linux-focused; USB permissions may require udev rules or sudo
  • No graphical user interface (command-line only)
  • Limited to ARM Cortex-M devices; does not support other ARM architectures like Cortex-A
  • No pre-built releases or packages; must clone and build from source
  • Documentation is limited to the README file and source code comments

Best For

Embedded systems development and debuggingFirmware reverse engineering of ARM Cortex-M devicesEducational tool for learning ARM CoreSight debug and trace technologiesHobbyist electronics projects involving STM32, nRF, or other Cortex-M MCUsAutomated testing and verification of microcontroller firmware

FAQ

What hardware debug interface is needed?
PyCS supports SWD debug interfaces such as ST-Link, J-Link, and CMSIS-DAP compatible probes. It communicates via USB using the HID or custom protocols.
Which target microcontrollers are supported?
PyCS supports a variety of Cortex-M based chips, including STM32, nRF, EFM32, Atmel SAM, and more. Run './pycs -l' to list all currently supported targets.
Is pycs free to use?
Yes, pycs is open source under the MIT license, so it is free to use, modify, and distribute.