raspberry piusb
I would like to wake up my desktop computer (Mac or PC) from sleeping using a Raspberry Pi Zero.
Is it possible to get the Zero to wake a computer over a USB connection? I can wake my Mac up using the mouse or keyboard so it seems possible that if I could configure it to send the same signals then I could.
I have read that one can turn the Pi into a 'USB gadget' – this may be the right approach or unnecessary.
USB is hot-pluggable, so you don't actually have to power down to remove/insert those (I don't know about HDMI though, so I'd keep powering down).
From an ELECTRICAL/ELECTRONIC/SOFTWARE standpoint there is NO problem with doing this. None of the equipment or the operating systems care.
From a MECHANICAL standpoint, you are adding wear and tear to the connectors. I did a quick search and I think your average USB connector is rated at somewhere in the neighborhood of 10,000 insertions. (That's two a day for 13 years). Some will wear out quicker than rated, some longer, but I'd say your computer USB connectors won't (from wear) be the first things to go. The hard drives will probably die first.
My bigger worry at that point would actually be that you're taking an increased risk of accidentally screwing something up by twisting a plug or accidentally leaning on a connector , or whatever. As long as you are careful, you should be able to do this safely for as long as you can stand swapping the cables back and forth.
On page 258 of the datasheet:
• 0 – VBUS: VBus flag
The value read from this bit indicates the state of the VBUS pin. This bit can be used in device mode to monitor the USB bus connection state of the application. See Section 22.10, page 255 for more details.
On page 255:
22.10 Plug-in detection
The USB connection is detected by the VBUS pad, thanks to the following architecture:
The control logic of the VBUS pad outputs a signal regarding the VBUS voltage level:
• The “Session_valid” signal is active high when the voltage on the VBUS pad is higher or equal to 1.4V. If lower than 1.4V, the signal is not active
•The “Vbus_valid” signal is active high when the voltage on the VBUS pad is higher or equal to 4.4V. If lower than 4.4V, the signal is not active
• The VBUS status bit is set when VBUS is greater than “Vbus_ valid”. The VBUS status bit is cleared when VBUS falls below “Session_valid” (hysteresis behavior)
• The VBUSTI flag is set each time the VBUS bit state changes
Not sure if this Is what your looking for but figured I would post it anyway.
Best Answer
Bit of background first:
Generally, USB itself is not a bus over which a device can be really woken up if it stopped working completely, because it's a host-polling based bus, i.e. the host PC must inquire the keyboard in regular intervals. If that host is completely shut down, nothing one can do.
However, being a host for a USB keyboard is relatively easy, and since host firmwares need to emulate PS/2 (or Apple desktop bus keyboards) for compatibility reasons, anyway, that was a feature easy to implement: simply let the firmware take over the USB bus, and ask all the attached Human Interface Devices (HIDs) whether they got input every couple milliseconds.
So, all you'd need to do is implement a HID gadget profile on your Pi.
Yes, that works, and it's about the easiest profile to implement.
Whether that is a sensible approach is a different question alltogether: The Raspberry Pi, when it comes to ARM SoC computers, is a relatively power-hungry device, so that it is actually worth the question whether running a Pi 24/7 to wake up a computer is worth it – if that computer is attached to a router via ethernet, for example, that could use magic Wake on LAN packets instead.