I’m wondering if connecting the SCK pin to the XTAL1 pin could be used to ‘wake’ dead AVR’s whose fuse has been accidentally set to external oscillator and don’t respond anymore.
Has anyone tried this?
I just tried this on my Olimex AVR-P28 board (with an AtMega8 on it) and it didn’t work. I even cut a track between the decoupling cap and the SCK pin to isolate it but the software doesn’t respond. I do see a nice clock on the pin with my scope, though.
I have no idea why it doesn’t work. 
i beleive when you program it the first thing it does is tick the reset pin. At this point there is no SCK yet. and this is where you need it.
It was a bright idea though.
AVR’s are programmed in ISP md through SPI. The SCK HAS to be(less than) 1/4th of the main clock or it won’t work…In your case you had the SPI clock running the same speed of the AVR clock…
Use another AVR to generate a faster clock signal, though, and you’re talking… the tiny2313 is particularly handy for this as all you need to do is set a fuse and it outputs its generated system clock on a pin.
bring up a 2nd microprocessor and jumper its clock osc pins to the dead AVR, along with GND.