One of the changes on the Rev 2 Raspberry Pi board, which I haven’t seen anybody write about yet, (apart from Eben in his original announcement) is the addition of two holes for a header at P6. These were added to enable a reset facility. Shorting those two pins together resets the processor.
This was too good an opportunity for my curious mind to pass up, so I decided to add a 2 pin header there and try it out.
As luck would have it
It just so happened that last week I was given an old PC, which I took apart for fun (and parts). One of the salvaged parts was a reset switch connected to exactly the right kind of (2.54mm) 2 pin female socket.
I had a stack of pin headers in stock already. So I just cut off 2 pins’ worth and soldered it into the P6 holes (with leaded solder, to minimise heat to the Pi).
Then I pushed on the connectors for the switch, booted up the Pi, logged in and let it settle.
And then I pressed the reset switch. And it worked. The Pi reset and rebooted without a hitch. :)
Will it bring the Pi back from a halt?
So having logged in again and tried it again, I shut the Pi down with
sudo halt. Then I thought mischievously to myself…
“I wonder what happens if you press it while the Pi is connected but powered down?”
So I tried it. And…
The Pi booted back up again :) So you can also use this header to bring your Pi out of a shutdown state, provided the power is still connected.
You don’t strictly need a switch
Of course, you don’t need to install a “proper” reset switch. A jumper would do, or even a paperclip. You don’t really even need to put a header on. You could short across the holes with your paperclip (it’s only a momentary connection). I’m not saying you should, but you could. It’s obviously the “preferred way” to use a header. I did consider putting a 2 pin socket there instead – to avoid accidental reboots – but the decision was made for me when I found the ready made reset switch. :)