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Attiny Bootloaders

Bootloaders are mysterious beasts - I have "bricked" many chips through clumsy setting and flashing of fuses on various micro-controllers. For instance, if you set the clock to an external 8Mhz crystal and then burn the bootloader, you will need an external 8Mhz crystal to either change the clock or to upload code. Makes sense in hindsight, right?

This "oversight" became such a regular occurrence that I ordered, and have used quite a few times, a high voltage fuse fixer (HVPP/HSVP programmer) which has brought back to life many an abused µC.

You can build your own HVPP if you wish, by just following these excellent instructions.

A large part of the confusion on my behalf arose early in my AVR dabbling when I bought a device marketed as a "programmer"

I had also at that time bought some dirt cheap DIP8 ATTiny13 chips so I was super keen to make a ... blinking led circuit? Loading up the famous blinky sketch on the Arduino IDE I plugged in the ATTiny13 into the cradle and then nudged the USB cable into a port on my computer and...

Due to not understanding the whole correct orientation of the chip thing, the ATTiny13 was literally smoking, the "programmer" was fried, and then the computer involuntarily shutdown.* Not the most auspicious start to my AVR programming life.

Very soon after this scarring experience I discovered the Arduino ISP sketch, found out how to hook up an Arduino to an ATTiny for burning fuses and programming, and forgot about the whole "cheap so-called programmer smoking up the room" episode.

Until recently that is! In order to conjure up topics for this blog and channel I literally grab a random component - and so I was fishing about for inspiration and pulled out one of these tiny DIP8 programmers from the buckets. Oh no! There were flashbacks including of course the well known smell of burning components (which was prophetic).

Nonetheless - given it is a few years on and perhaps I could be a bit wiser (?!), I plugged in an ATTiny85 (the correct way), and loaded up some blinky goodness, then pushed "compile and upload" only to be greeted with amused silence from the Arduino IDE and some distinctly non-blinking of LEDs.

So here I am again (with the benefit of hindsight and experience?) seeing if I can usefully employ these devices. Crucial to the process is the idea that this little board does not have any USB interface and so we need to use a "virtual USB" protocol encapsulated in a bootloader. Which came first, the chicken or the bootloader?

Most of the work in this area has been done by the "MicroNucleus" team. The plan for this little board is thus to:

1. Load the Micronucleus bootloader to a "vanilla" ATTiny85 using USB-ISP
2. Program the ATTiny85 directly from the board using the Micronucleus bootloaders V-USB protocol
3. Try to upgrade/load the bootloader and program using the board only
4. Try to extend the bootloader from ATTiny85 to ATTiny13

See below for the video of these steps and their various successes.

*postscript: I blew up another one in the exact same manner making this post/video <sigh>