On Wed, Oct 7, 2026 at 7:12 PM <[email protected]> wrote: > On Wednesday, October 07, 2026, at 5:20 PM, Dan Cross wrote: > > I'm mystified about where you came up with the 1.5A number you mentioned > > earlier. > > It's the amperage provided by the powered port of my T420. At least, I read > that somewhere, might have that wrong.
Are you sure that's not max source current the port is capable of providing? Was it actually drawing that with your device plugged in? > On Wednesday, October 07, 2026, at 5:20 PM, Dan Cross wrote: > > Does the laptop tell you how much current the port is drawing when these > > things are plugged in? > > From here: https://forums.linuxmint.com/viewtopic.php?t=366919 > "As far as I'm aware not any system's USB-implementation has hardware to > measure actual, live draw; this would be information unavailable to any > software, be it Windows, Linux or BIOS/UEFI-based." I'm not sure that I trust that good ol' rene over at the Linux Mint forums know definitively, but it is true that you can get the device to tell you it's _advertised_ max power, but it can still draw more. > and: "When you type usb-devices | less into a terminal you're presented with > your devices' advertised maximum draw in the MxPwr fields." > > I get MxPwr=98mA, which is tiny. At least, that is the only output that is > for a usb device, so.. so so much for the 1.5 number I quoted above. -_- Yeah, I doubt that power is the problem. If the device were really drawing that, it's likely a hardware over-current protection would kick in and shut it down. > On Wednesday, October 07, 2026, at 5:20 PM, Dan Cross wrote: > > how would you know whether it was the mouse, or the adapter? > > This goes to show how little I thought about the problem. Reflecting on it > now, I thought of the adapter as being just a bunch of wires, not an active > electronic device that would actually draw power. Without the mouse > attached, I assumed it would just act as an extension of the pi, with no > current flowing. With no current flowing.. no power consumed. So the fact > that it reacted at all with just the adapter attached was an eye-opener. My guess is that this is a software problem, or hardware doing something funky like split high- and low- speed transactions that the dwc_otg controller in the Pi doesn't deal with well. - Dan C. ------------------------------------------ 9fans: 9fans Permalink: https://9fans.topicbox.com/groups/9fans/Td94105a3d5018162-Me5c77aa61f31ea5fe9a82519 Delivery options: https://9fans.topicbox.com/groups/9fans/subscription
