USB transaction failed warnings with AKAI MPK Mini MIDI controller

[daparker26]

Hi Rene and anyone else who could help!

I am using Circle Step 45 on a Raspberry Pi 1 (B2). I'm trying to use an AKAI MPK Mini 3. However, once Circle recognizes it, I get a string of these warnings:

00:00:06.44 dwhci: Transaction failed (status 0x202).
00:00:06.44 dwhci: Transaction failed (status 0x202).
00:00:06.44 dwhci: Transaction failed (status 0x202).
00:00:06.45 dwhci: Transaction failed (status 0x202).

It seems to still work—it detects when I press the keys, but these messages are concerning. I assume I can just suppress them, but I wondered if there was a fix or workaround? I don't know a lot about USB, so I don't really know where to begin. I've added usbspeed=full in my cmdline.txt file, but it doesn't help. Thanks!

[rsta2]

Hi Daniel, this problem is caused by an unfavorable timing on the USB. These messages are not critical, but it is recommended to enable the system option REALTIME or even better USE_USB_FIQ by adding the following line to the file Config.mk in your project root:

DEFINE += -DREALTIME

or

DEFINE += -DUSE_USB_FIQ

Everything must be rebuild, after adding this.

REALTIME suppresses log messages from IRQ handlers. Because IRQ handlers cannot be interrupted by another IRQ, the system timing may be bad, when a log message is generated in an IRQ handler and for example, the screen has to be scrolled because of this. This happens all inside the IRQ handler and takes milliseconds. With REALTIME enabled, this does not happen.

USE_USB_FIQ uses the FIQ for the USB host controller driver, which gives the best USB timing and is recommended, but cannot be used, if the FIQ is used for some other purpose (e.g. the serial device).

[daparker26]

Thanks, Rene! Enabling REALTIME fixed the issue. However, with REALTIME enabled, the touchscreen is unresponsive. Unfortunately, the touchscreen stopped powering on before I could get around to troubleshooting the issue (I had been having intermittent issues with it since I first got it).