USB host issues and power supply

EDIT: after some troubleshooting, looks like I have a bad cable that doesn’t provide USB host power, so this should not be relevant to anyone else.

I’ve started testing some USB controllers with Magus USB host and so far it doesn’t look very promising. Magus itself is powered from 9V PSU (advertising up to 1.67A). All devices work if I route them through a PC instead of connecting directly to USB host.

  • Linnstrument 128 - doesn’t power. Manufacturer rated to use 0.3 A, but 0.5A is recommended.

  • OP-1 - it’s battery powered, but even with fully charged battery or USB charging disabled I still don’t get MIDI working. If I use USB splitter with external power (1A), it works. Disconnecting power or device and then connecting it again gives me the “USB Host unrecovered error” error message and MIDI doesn’t work until reboot. I suppose that’t the dreaded USB host issue that @mars mentioned before.

  • Novation Launchpad PRO (not the latest, but the one that had partial open source firmware support) - wouldn’t power from Magus (manufacturer recommends using 12V 1A PSU, but doesn’t tell how much exactly would be consumed on USB). If powered from external PSU it doesn’t see Magus. This is obvious because its default firmware switches to keyboard-like mode if it’s connected to anything, otherwise it plays rainbow animation.

Found out something else about this error. Another way to get it is to boot device with OP-1 turned off, but connected to USB host. Then it appears when OP-1 boots. So it’s not necessary happening after disconnecting device, not plugging it is sufficient to reproduce it.

Also tested with Beatstep Pro (manual says it requires at least 500ma at 5V) - won’t power from host and has the same connection issue. But I do have at least one other device that is not so power hungry and it used to be possible to power it from Magus host.

The Magus should supply up to 500mA with no problem. If the device draws more than this, there is a power switch which automatically switches off. You should then see an error message: USBH PWR Fault.

Some of the devices we’ve tested with successfully are:

  • Alesis Q49
  • Arturia Keystep
  • Korg NanoKontrol
  • Akai LPK-25 Wireless (requires latest development branch to work)

I’ll see if I can get hold of a Beatstep or OP-1 to try with. Linnstrument might be harder!

In case of Launchpad (and OP-1), the device is not powered by USB itself. But OP1 only connects if I use splitter that provides power externally. I don’t understand all details of USB enumeration and power supply, but it seems like we could have sort of race condition here between providing power and starting enumeration. I will try to figure out what’s going on with debugger.

I didn’t get that power error in any of those tests, that’s certain.