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stefanrueger / urboot

Small AVR bootloader using urprotocol
GNU General Public License v3.0
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USB urboot for ATmega32U4 and other USB AVRs #12

Closed mcuee closed 1 year ago

mcuee commented 1 year ago

Caterina bootloader (USB AVR109) is popular for ATmega32U4 based boards (eg: Arduino Leonardo and Arduino Micro). However they are a bit troublesome to work with avrdude (1200bps touch).

Please refer to the following discussion in avrdude.

It may be a good idea to port urboot to ATmega32U4 (and similar) with USB to Serial support.

stefanrueger commented 1 year ago

USB to Serial support

I have insufficient experience with USB to serial. Urboot assumes there is a serial line to talk to, and the rest is abstracted away in the uploader (eg, AVRDUDE). Are you talking about parts that have native USB support in the AVR and that would use something else than an USART for comms? That kind of stuff would need a PR from someone else who has the experience.

Other than that the Avrdude issue #788 is independent from bootloading itself, so invalid here.

mcuee commented 1 year ago

Are you talking about parts that have native USB support in the AVR and that would use something else than an USART for comms

Basically the idea is the same as Caterina bootloader (USB to Serial + AVR109) so that we do not need a seperate USB to Serial chip to use urboot (USB to Serial + urboot) since the USB AVR can act as a USB to Serial chip ifself by implementing USB CDC-ACM FW. It still uses the USART in the end for COMMs.

Reference: https://github.com/arduino/ArduinoCore-avr/tree/master/bootloaders/caterina

mcuee commented 1 year ago

There is a potential issue of USB VID/PID to use though.

stefanrueger commented 1 year ago

I have carefully looked at the USB interface of these parts in the data sheet. It's some 30 pages of dense description and I imagine it needs a lot of code to directly read/write USB serial data. I am tempted to predict that this will never happen. Urboot is designed to be compact (it's roughly half the size of optiboot), so that's not the type of project to start spending a lot of code in the bootloader for USB to serial conversion. That really is better done by an USB cable/chip.

mcuee commented 1 year ago

Fair enough. I agree this is out of scope.