Workaround for “Cannot find an ST-LINK” when Using STLinkReflash for J-Link OB Conversion

12 October 2020 by Phillip Johnston • Last updated 14 December 2021

In a hurry? Jump to the solution.

I was bringing up a new Nucleo-L4R5ZI board for one of my internal projects. I had trouble flashing the device using the opensource stlink command line tools. Rather than wasting too much time diving into that (apparently long-standing) issue, I decided to boot up my Windows VM and convert the onboard ST-Link into a J-Link using Segger’s STLinkReflash program.

Strangely, STLinkReflash couldn’t detect my board:

ERROR: Cannot find an ST-LINK, multiple ST-LINKs plugged in, or ST-LINK is in use.

So instead of wasting my time debugging the errors I was seeing with st-flash, I spent an entire morning trying to figure out why my ST-Link couldn’t be detected!

Debugging Summary

First thing – I checked to make sure I had the correct (and latest) drivers installed. I also manually uninstalled the drivers and re-installed the latest versions just to make sure. No change there.

I also noted the STLinkReflash version for future reference, in case an update comes in the future:

STLinkReflash Compiled Aug 12 2019 10:30:05

I pulled out two other Nucleo boards that I have on hand to see if this was an isolated problem. One of them was successfully re-flashed, but the other board triggered the same error. Obviously the re-flash tool itself works, somehow this was board dependent.

Then I figured it might be a firmware version problem. Of course, it’s always good to update to the latest firmware version when you run into trouble. I downloaded the latest ST-Link firmware update tools. What immediately jumped out at me is that the update tools had no problem detecting these ST-Link boards, but STLinkReflash definitely did.

Of course, I had to stop at this point and read the manual. I checked Segger’s website and confirmed that all of my boards were supported by the STLinkReflash tool. No obvious notes were found on the internet for this issue. There were no real requirements other than “install all of the necessary drivers before using this tool.”

Thinking this might have something to do with the firmware version itself, I reverted my “working” board back from a J-Link to an ST-Link so I could try updating that board. The version restored by J-Link was. definitely older than the currently available versions. I updated this device to use the latest firmware, and now it was in the “Cannot find an ST-LINK” camp.

Luckily, ST provides older versions of the firmware upgrade tools on their website. I went through them all.

The following versions did not play nicely with STLinkReflash in my setup:

• 2.37.26
• 2.36.26
• 2.35.26
• 2.34.25
• 2.33.25

However, the oldest version currently available does work: 2.32.22!

Two out of the three boards I had on hand were able to downgrade straight from 2.37.26 to 2.32.22. However, one board was never successfully detected by the 2.32.22 update program, so I had to perform a two-stage downgrade process. First, I reverted to 2.33.25, then I reverted to 2.32.22.

At this point, I sent Segger a note about this issue with my findings. The Segger team responded:

We are not aware of any issues with recent versions of the ST-Link firmware + SEGGER STLinkReflash utility. We will check if we can reproduce this behavior. If reproducible, we will of course investigate and fix it if required.

They later wrote to confirm that they could not reproduce this issue. Segger noted the software versions they tested against:

• Latest version of the ST-Link Reflash Utility (2019–08–12)
• Latest ST-Link USB drivers: https://www.st.com/en/development-tools/stsw-link009.html
• Latest ST-LINK firmware upgrade: https://www.st.com/en/development-tools/stsw-link007.html
• J-Link software V6.86d
• Windows 10 (x64)
• Evalboard NUCLEO-F767ZI
• Evalboard NUCLEO-L4R5ZI

There’s definitely a possibility that something is off with my setup, or that a Windows 10 VM inside of Parallels running on MacOS has some impact on the bug. Either way, I wanted to note my findings in case anyone else runs into this issue.

The Solution

First, confirm that you have installed the latest J-Link software package (V6.86d at the time this article was written), in addition to the ST-Link USB drivers. Try to upgrade your device once more.

If you’ve installed these components but still cannot upgrade your device, downgrade your firmware:

1. Download version 2.32.22 of the stsw-link007 software package from the ST website (found in the “Previous Versions” dropdown)
   1. I’m mirroring the file just in case it disappears before Segger gets the problem resolved
2. Unzip the archive and load the proper program for your OS
3. Update (aka downgrade) your ST-Link firmware to version 2.32.22
   1. If your device isn’t detected by the update program, try reverting to 2.33.25 first.
4. Close the ST-Link update program (important!)

And then run STLinkReflash to upgrade the device to a J-Link.

I’ve observed that sometimes STLinkReflash crashes suddenly during the upgrade process when talking with firmware version 2.32.22. If this occurs, just re-open the app and re-run the upgrade process. I have not seen it crash the second time.