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+--- Thread: Midi Out issue on linux (/showthread.php?tid=19)
Midi Out issue on linux - devin - 05-13-2026
I'm running into an issue with midi out support.
See the configuration below, as simple as I could make. I can see the onboard led change when I press the user key button on my board. I can also see the live values reflect what I expect.
What I know:
- Seem to only have issues with Linux (have successfully run it on windows)
- Can see the midi device on Linux ( list in terminal 'amidi -l' and can see the device on https://hardwaretester.com/midi )
- Cannot see any events on the bus
What I have tried:
- Have tried both channel 0 and channel 1
- Have tried a few indexes
Maybe it is some Linux permission issue? Not sure.
Running:
Board: Homemade FrankenBoard based on this dev board: https://stm32-base.org/boards/STM32F103RCT6-FK103M2-V1.0
Bootloader: xperimental/8MHz 1.5
Firmware: xperimental/8MHz/ 1.5
RE: Midi Out issue on linux - iforce2d - 05-14-2026
Hi Devin
Thanks for the report.
With the two RCT6 boards I have here (regular iomixer and one dev board from AliExpress) I was able to send MIDI messages to Fedora Linux ok. But both of the two 'blue pill' variants showed the symptoms you describe - the device appears but no message events are received. The 'blue pill' boards use a CBT6 but I don't think that should matter. The other issue we discussed via email (pullups on the USB D+ line inhibiting soft-reset) should not matter either... I think.
Since you're also using a RCT6 the only point of difference seems to be the Linux version. I will try this with Arch Linux next, although that might take a bit longer.
While I was investigating this I noticed some code that was not handling the recent change to support 8MHz properly, so I fixed that. It did not help with my blue pills but there is a small chance it's related to this issue so it's worth giving it a try. I have updated the file here (main app only): https://iomixer.com/releases/firmware/xperimental/8MHz
Since you had it running ok on Windows you probably don't need any help with the configuration side, but for others coming to this thread who are not familiar, I will leave a link to the video you mentioned here: https://www.youtube.com/watch?v=Njruoow2stw
In particular note that the port to use for events going from the iomixer to the PC is "iomixer MIDI out". Also, on Linux using channel 0 in the configurator seems to result in channel 1 in the hardware tester page.
RE: Midi Out issue on linux - devin - 05-15-2026
Man, maybe we can brainstorm somethings I could try on my end before you setup a whole new distro. That is such a pain in the ass. I think I have a headless server running Ubuntu. Let me try that first.
Let me know if there is anything that you know I could try. Is there a way to dump the raw USB data to see if it coming but it gets lost in the kernel stack somewhere? I would just hate for you to wast a bunch of time setup up Arch for it to make no difference. Especially since I am running FrankenBoard. It is much more likely that is the cause then the Linux distro.
Sorry for the spam. But I was able to get it to work on my headless mac mini server that is running Ubuntu. So the theory that something is going on at the distro level is more likely. But it also means that I should chase it down if I care.
I'm actually running CachyOS which is a based on Arch but it has custom kernels. I'm running an old laptop and I was hoping to get a little more performance. Anyway, please don't chase down my esoteric setup. Let me see if I can get something more concrete to you.
Devin
RE: Midi Out issue on linux - devin - 05-20-2026
Well I tried a bunch of things and could not figure out where it was breaking down usb/midi stack. But then I decided to see if upgrading the OS would help (since Arch has a rolling release). And it now works just fine. So I guess I had something out of wack or there was a bug that was fixed. I don't know.
Thanks for look into this a little. Sorry for raising a bit of a red herring.
RE: Midi Out issue on linux - iforce2d - 05-21-2026
Not a problem at all. I'll still need to figure out why the blue pills were not sending messages, so it was good to know about that.
Glad to hear it was cleared up, since that was the OS you wanted to use. I mean who wants to use a smelly Windows or Mac?
