I'm running some hardware that's drawing more power than my computer's USB port can supply reliably, so I'm using a 5v external supply. The MBED appears to work fine but if I plug it into a USB port while it is running it is not recognised. If I remove external power so the MBED is powered by USB then it is recognised, but then the target hardware can cause power sags that cause file writes to fail. This is going to cause me some serious power-sequencing issues unless I can find a USB hub with enough power.

Is it the case that the MBED only attempts to initialise its USB port immediately after reset, and if no host is detected then the port is left un-configured?

I'm also having this problem. Has anyone got any advice/a solution?

Try running your hardware only on the external 5v, and power your mbed via the usb, just remember to connect the grounds together. Note: A USB 3 hub will give you more current.

Well, it does not work even with no hardware attached (other than what's on the evalboard of course). I had USB CDC working some time ago with "pure silabs SDK" (no mbed) and it was working fine on the same board, so it has something to do with mbed...

BTW. same thing happens after a manual reset of the chip (with power going through debug usb port) - it does not enumerate and manual replugging is necessary.

Hi guys,

I will start to investigate this. In the future, please ask your question on the relevant mbed board page, since that gives me a notification, instead of me having to stumble across a thread in the forum :)