I have picked up the ArduinoISP on Due experiment.
I observed a problem when stopping and restarting SPI.
A fix is proposed here:
http://forum.arduino.cc/index.php?topic=165497.0
I can't program nor run my attiny at 3V3, allthough according to the datasheet it should work
Not being able to run it at 3V3 was a silly wiring error on my side.
However I still can't program the attiny85 from my Due. I figured this could be because of the 3V3 or the SPI speed or a combination of both.
So for comparison, I hooked up the attiny to an atmega328p@16MHz that I powered at 3V3 and that runs ArduinoISP. This worked with the standard SPI_CLOCK_DIV128. Then I tried higher SPI speeds. SPI_CLOCK_DIV64 still works, but SPI_CLOCK_DIV32 does not! So 4MHz/32 == 125kHZ seems too fast! On the Due I use clock divider 255 resulting in 84MHz/255 == 329kHz. So speed seems to be the problem: the Due is too fast.
To compare this experimental result to the spec: the tiny's lfuse is 0x62 which means 8Mhz internal with a clock divider of 8 => 1MHz cpu clock. The spec says the duration of an SPI SCK must be 2 cpu cycles high and 2 cycles low => max SPI speed is 250 KHz. If I interpret the data sheet well, my experiment should have worked. My experimentation board setup could be responsible for this though this stuff works for an atmega328p@16MHz as target... anyway 250kHz is still slower than the Due's slowest SPI speed.
Has anybody similar experiences with the tiny's max ISP speed? (I could have mis interpreted the data sheet).
I see no way to configure the Due for a slower SPI.
It seems a bit over the top but I am going to try to use software spi for this...