It appears that in OpenOCD package version 20200305-0.10.0 the “adapter_khz” command is no longer supported. From looking at the OpenOCD commit log it appears that this has changed to “adapter speed”. It is easy enough to fix a project that was created using the previous version of OpenOCD by editing the command line manually in the “VisualGDB Project Properties” window but editing or changing the “Set JTAG/SWD frequency to:” dialog box and tick box result in the legacy command being added to the command line again. I’m guessing that VisualGDB will need to be updated so that the project properties windows exhibits the correct behaviour.
I have checked and there are no updates for VisualGDB or the OpenOCD plugin.
Thanks for pointing this out. Indeed, the command used by OpenOCD to specify the frequency has recently changed and the projects created earlier would still use the old command.
We have released another update to OpenOCD that automatically substitutes the old command with the new one. Please feel free to update it via VisualGDB Package Manager and it will work out-of-the-box.