Problem programming 3.3v/8Mhz board

[daryll]

Hi folks,

I built my USBtinyISP and and the EMSL dev boards. I popped a '168 in to it and could make the LED blink. So the USBtinyISP itself seems to be fine. That was just for testing.

Now I'm trying to make this work with a board I'm building. The setup is Linux with atmega32u4 that I want to run at 3.3v/8Mhz. I'll also mention that crystal I've got in there is 16Mhz, because I thought the mcu could do a divide by two on it.

If I run avrdude with just the -c usbtiny -p m32u4. It "mostly" reports the correct signature and then tells me that it failed to read the lfuse and was giving up. I say mostly reads it correctly because sometimes it corrupts the signature as well.

I can read all the fuses and things seem to work nicely if I let the USBtinyISP provide 5v, but there are other pieces of my circuit that can't tolerate that and I don't have an easy way to avoid them getting power. (Probably something to fix for the next version.)

It seems like this is either a problem with the low power or clock making it marginal. Any idea what I should be doing differently? I'm trying to push past using an Arduino in to making my own board, so I'm probably just doing something dumb.

[westfw]

I just had an interesting and possibly relevant experience with my own Arduinos; there are a bunch of different fuse settings for the crystal oscillator, and I managed to create an ATmega8 that ran fine in assorted Arduinos w 16MHz crystals, ran fine in an Adafruit BoArduino with resonator, but would not run at all (wouldn't even respond to programming commands) in my SSS clone with a different brand of resonator. Changing the fuse settings (to use the "full swing" oscillator instead of the "low power" oscillator) caused it to work everywhere...