Fixing STM32H7 Flash Errors With Probe-rs

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Fixing STM32H7 Flash Errors with probe-rs: A Troubleshooting Guide

Hey guys! Ever run into a wall trying to flash code onto your STM32H7 board? Specifically, have you seen the dreaded send_jtag_command 242 failed: SwdDpError when using probe-rs? I recently wrestled with this issue while working with an STM32H743VGT6 and figured out some stuff, so I wanted to share my experience. It's frustrating when you're just trying to get your code running, and instead, you're staring at a wall of errors. Let's break down the problem, what causes it, and how we can get things working smoothly again.

Understanding the Problem: The SwdDpError and its Friends

First off, let's unpack this SwdDpError. This error generally means the debugger is having trouble communicating with the chip. Specifically, in my case, the probe-rs tool was reporting this error during the shutdown sequence after flashing the code. The code seemed to flash correctly, but the debugger couldn't properly deconfigure the device. This is a common hiccup when working with embedded systems, but it's solvable.

 WARN probe_rs::probe::stlink: send_jtag_command 242 failed: SwdDpError
 WARN probe_rs::probe::stlink: send_jtag_command 242 failed: SwdDpError
 WARN probe_rs::probe::stlink: send_jtag_command 242 failed: SwdDpError
 WARN probe_rs::session: Could not clear all hardware breakpoints: An ARM specific error occurred.

Caused by:
 0: The debug probe encountered an error.
 1: An error which is specific to the debug probe in use occurred.
 2: Command failed with status SwdDpError.
 WARN probe_rs::probe::stlink: send_jtag_command 242 failed: SwdDpError
 WARN probe_rs::session: Failed to deconfigure device during shutdown: Arm(Probe(ProbeSpecific(BoxedProbeError(CommandFailed(SwdDpError)))))
Error: An ARM specific error occurred.

Caused by:
 0: The debug probe encountered an error.
 1: An error which is specific to the debug probe in use occurred.
 2: Command failed with status SwdDpError.

The stack trace above is the exact error I encountered. You'll notice multiple WARN messages related to the SwdDpError. These warnings are a good indication of where the issue lies. They're telling us that the probe-rs tool, specifically the ST-Link part, is failing to send JTAG commands correctly. This can happen for several reasons, from connection issues to probe firmware problems, or even specific hardware quirks of the STM32H7. In my case, even though the flashing appeared successful, the debugger wasn't able to finalize the process, leading to this error.

The Challenge

The central challenge is ensuring the debugger can correctly communicate and control the device throughout the flashing and debugging process. The root cause can be complex. In my case, after much trial and error, I found some of the most common causes and ways to resolve these issues.

Troubleshooting Steps: What to Check

1. Connection and Hardware Basics

  • Verify your connections: Double-check your SWD/JTAG connections. Ensure all the wires are securely connected from your debug probe (like an ST-Link) to the target board. Loose connections are the bane of any embedded developer's existence. I cannot stress enough the importance of making sure your wiring is spot on.
  • Power: Confirm your board has sufficient power. Sometimes, undervoltage can cause communication errors. Make sure your target board is receiving adequate power.
  • Probe Firmware: Update your debug probe's firmware. Outdated firmware can lead to compatibility problems. Most probe manufacturers provide tools to update the firmware. Updating your ST-Link to the latest firmware could solve the problem.

2. SWD vs. JTAG: Choosing the Right Interface

  • SWD is often preferred: For STM32H7 devices, SWD (Serial Wire Debug) is generally recommended over JTAG. SWD uses fewer pins and is often more reliable, especially at higher clock speeds. So, ensure your probe and target are configured to use SWD.
  • Probe-rs configuration: When running probe-rs, make sure you're specifying the correct interface. You can usually do this in your cargo run command or probe configuration files. Check the documentation on how to set the correct communication interface, as the specific syntax varies.

3. Probe-rs Configuration

  • Chip Selection: Double-check that probe-rs is configured for the correct chip. This might seem obvious, but typos happen. Make sure you are using the exact chip name for your STM32H7. For example, for my STM32H743VGT6 device, I ensured that probe-rs was correctly configured.
  • Speed: Experiment with the SWD/JTAG speed. Sometimes, a faster clock speed can cause communication problems. Try reducing the speed using the --speed option in probe-rs. For example, you might run probe-rs run --chip stm32h743vg --speed 1000.
  • Connect Under Reset: This setting can sometimes help establish a stable connection. Try using the --connect-under-reset option. It's often helpful when the target is not cleanly starting up. This forces the probe to connect while the target is held in reset, which can resolve connection issues.

4. Code and Project Setup

  • Minimal Example: *Start with a simple