As for USB3.0 spec USB Host can provide up to 900mA to a device connected 0.9A*5V=4.5W total. USB2.0 has no more than 500mA so <=2.5W USB device can be connected.
I'm sure AR9271 has <2.5W during firmware loading procedure but it must be checked in case of fit-pc has out of spec power per USB2.0 port. Going to perform some checks soon. On 7/27/2018 2:22 PM, Kevin Chadwick wrote: > On Fri, 27 Jul 2018 12:22:08 +0300 > > >> There is no any external hub or cable between AR9271 usb stick. I >> attach it directly to AMD GX-420CA SOC with Radeon(tm) HD Graphics >> PC. Firmware does not load when it attached to any of USB2.0 ports. >> But when it attached to USB3.0 AR9271 works without any errors. > > > USB3 provides more current than USB2, so this may make sense with the > current theory of some USB2 boards not supplying enough power for > these devices. > > USB has to protect against user insertion, damaged ports etc. so surges > are filtered more so than required for USB via pci-ex. > > I wonder if the firmware loading speed can be dialed down so that less > power is required (perhaps it saves memory by verifying as received) or > more likely the issue occurs after upload completion? Is the open > firmware a different size or sets different power settings? Are any > power affecting settings available before firmware upload? > > If the power usage is close to the limit then it may cause micro > reset/failure a varying percentage of the time. > > Sorry if all this has already been considered. >
