README.md

Timonel - ATtiny85 I2C Bootloader

Timonel is an I2C bootloader for ATtiny85 microcontrollers. The aim is to enable AVR firmware updates in scenarios where there is a more powerful MCU (ESP8266, Arduino, RPi, BeagleBone, etc.) acting as I2C master and one or more Tiny85 as I2C slave performing peripheral functions.

Some possible cases:

• A small robot controlled by Raspberry Pi where the specific functions of each limb are delegated to several Tiny85 through an I2C bus.
• Multi-sensor systems, where each Tiny85 is a node that handles one or more sensors.
• etc ...

In these examples, it's handy to have the chance of updating the AVRs firmware straight from the I2C master. But, so far, I haven't found an I2C bootloader that fits directly the Tiny85, addressing its limitations:

• It doesn't have a specific hardware for I2C, only the USI.
• It lacks a protected memory area for the bootloader.
• It is not possible to redirect the interruption vectors to the bootloader.

That's why I started writing this one.

Usage:

• Install "timonel-bootloader" on the Tiny85 (bare chips or Digisparks).
• Compile your program and convert the generated .hex into an array of bytes to be included in "timonel-I2Cmaster". (e.g. const uint8_t payload[size] = { 0xaa, 0xbb, ...}; ). Use "tml-hexparser" for helping to create the array.
• Install "timonel-I2Cmaster" containing the generated payload in an arduino-compatible MCU (It has been tested with ESP8266 ESP01 and NodeMCU).
• Connect both chips by I2C.
• Open an asynchronous terminal (e.g. MobaXterm) connected to the serial port of the I2C master (9600 N 8 1).
• Run the commands shown on screen for erasing and flashing new firmware on the Tiny85 (more details on the steps necessary will be published later).
• It is also possible to update the bootloader itself thanks to the micronucleus' upgrade program.

Version History:

v1.0 - 2018-10-05: Functional Release (Optional features implemented. See it working).

v0.9 - 2018-09-29: Functional pre-release (Temporary page buffer and other minor issues solved).

v0.8 - 2018-09-16: First functional pre-release.

v0.7 - 2018-09-07: Non-functional.

v0.4 - 2018-08-10: Non-functional.

Credits:

I would like to thank the guys @ AVRFreaks.net, specially joeymorin, clawson and donblake) for sharing their vast knowledge and technical advice in general. Also to the micronucleus developers, for showing us the way to go regarding Tiny85 bootloaders.