Maximum usb current


#1

any idea how much is the maximum current draw allowed from the usb3 ports on the 960?


#2

I think they are build around the USB3 spec without any support for battery charger profiles. The hardware current limiters are configured to kick in somewhere around 1000mA to 1200mA (per port) which is enough to meet the 900mA required by the spec for a powered hub and the on-board hub is tied with defaults that disables any support for battery charging.


#3

oh good, 900mA would be plenty. I will be receiving a portable touchscreen soon that takes power from usb and uses the same usb for touch as well… 900mA would be more than enough to power it.


#4

hi ric96

Could you update how this ended, I’m looking for a touchscreen too.
What touch screen did you use, did you get it working?


#5

@joris:

USB powered touchscreens work very nicely as far as available power goes,
HOWEVER, you may run into issues where the HDMI receiver is USB powered. If your “touchscreen” is actually a complete USB powered touch monitor, then this applies to you.

The problem has to do with when the USB power is switched on. If the USB power is not applied early enough for the HDMI receiver to respond to probing, then the kernel will fail to configure the display.

Unfortunately, the USB power is switched on by the kernel, which leaves very little time for the HDMI receiver to start up. With the displays I’m using, it starts up correctly roughly 10% of the time if I power the HDMI receiver from the USB. If I plug the display into an external power supply, it starts up correctly 100% of the time, and once its up, I can switch it over to the hikey960’s USB port.

The way I’ve worked around this issue is by powering the display from pin37 of the LS connector, which is a 5V source that is immediately powered on with the board; https://www.96boards.org/pinout/pin37_5v.html

This problem is strictly TIMING related and has nothing at all to do with the available current.