USB discussions getting a bit heated

Here are some results i ran into when using cheap powered hub.

Initialy they may seem incompatible with th PI, but it could be due to some compromise in the design/production run to cut pricr down.

I ordered some cheap 7 port power USB hub (like 3 for $12) with the power supply included.

on my 1rst attempt i connected my PI to the hub for both power, keyboard and mouse on the hub.

The PI would start to boot and then keept on rebooting.

I removed the keyboard and mouse, no change.

The supplied power supply was rated for 5v 1A only, clearly insuficient current rating. so i used a 5v 2A supply i had left over.

I reconnected everything back, then the PI booted till it got to the USB port detection and then it was looping into the USB detection sequence. Then i noticed the micro usb plug was NOT connected on the PI ????? The PI was receiving power from the normal USB jack instead.

I then connected the micro USB plug and reapplied power, now the PI booted normaly. But the keyboard and mouse where erratics.

I decided to look inside the USB hub case and i found a jumper that connected the external power supply to the +5v side on the incoming usb connector from the PI.

Then i proceded to remove said jumper. Now the PI would not power on from the hub, good.

So i connected the micro usb cable to the powered hub along the keyboard and mouse.

now they are all behaving properly.

So my theory is that when the jumper wire was installed in the hub and you use the same hub for both power and expansions some current loops may be created inside the PI and cause some undesirable behaviour.

Here are some results i ran into when using cheap powered hub.

Initialy they may seem incompatible with th PI, but it could be due to some compromise in the design/production run to cut pricr down.

I ordered some cheap 7 port power USB hub (like 3 for $12) with the power supply included.

on my 1rst attempt i connected my PI to the hub for both power, keyboard and mouse on the hub.

The PI would start to boot and then keept on rebooting.

I removed the keyboard and mouse, no change.

The supplied power supply was rated for 5v 1A only, clearly insuficient current rating. so i used a 5v 2A supply i had left over.

I reconnected everything back, then the PI booted till it got to the USB port detection and then it was looping into the USB detection sequence. Then i noticed the micro usb plug was NOT connected on the PI ????? The PI was receiving power from the normal USB jack instead.

I then connected the micro USB plug and reapplied power, now the PI booted normaly. But the keyboard and mouse where erratics.

I decided to look inside the USB hub case and i found a jumper that connected the external power supply to the +5v side on the incoming usb connector from the PI.

Then i proceded to remove said jumper. Now the PI would not power on from the hub, good.

So i connected the micro usb cable to the powered hub along the keyboard and mouse.

now they are all behaving properly.

So my theory is that when the jumper wire was installed in the hub and you use the same hub for both power and expansions some current loops may be created inside the PI and cause some undesirable behaviour.

The USB upstream A-B backfeed that you describe is what causes the official "Pi Accessory" 7-port Dynamode hub to fail with the Pi, as I described in this thread ---  http://www.element14.com/community/thread/19316?tstart=30  .

I'll probably hack out the backfeed path or insert a diode some day, but for now it's working fine with Intel PCs.

Unfortunately the Pi's USB problems go far beyond just being succeptible to backfeed from cheap hubs.