The README refers to the image size as a 4-byte value. However, it is implemented in Optiboot.c as a 2-byte value. This means that images can be no larger than 64KiB, which is smaller than the 128KiB program memory of a MoteinoMEGA. In order to support larger programs, at least one more image size byte should be added.

Hi!

While troubleshooting some reset loops occurring when doing soft restarts, I noticed that WDRF is not cleared when turning off the watchdog. WDE is always set when WDRF is set causing a reset loop. Clearing it fixed my problem.

Many thanks for the great code!

void watchdogConfig(uint8_t x) {
  if (x == WATCHDOG_OFF)
	MCUSR &= ~(_BV(WDRF));
  WDTCSR = _BV(WDCE) | _BV(WDE);
  WDTCSR = x;
}

Does this support the SAMD21?

This line suggests that it doesn't, but I've read that the Moteino M0 supports OTA updating?

Thanks!

I just encountered a bug on a project that I traced to DualOptiboot.

The issue was that raw writes to the SPI pins (SK, MO, MI) were not working as expected in the main code. This only occurred on firmware reloads, not during normal power ons making it a particularly devious bug.

I think the issue is that in some situations DualOptiboot exits after loading new firmware but does not disable the SPI pins.

I fixed the problems by adding this line to my code. Perhaps you should check the codepaths and make sure this is done before the bootloader exits.

SPCR &= ~_BV(SPE);

I burned the Dualoptiboot_v5.0_atmega328_8mhz_57600baud_BlinkD9.hex to an Arduino pro mini (8MHz) using Sparkfun's pocket AVR programmer with AVRDude.

I changed the fuse values according to this diagram:
https://www.flickr.com/photos/15304611@N03/10585364014

Then I tried to program the board within Arduino IDE version 1.8.13, using an FTDI USB-to-Serial adaptor, with the Blink program.

Arduino terminal gets stuck at the synchronization stage. It seems that the STK-500 emulator cannot communicate with the board.

Am I doing something wrong? Is there any solution to this problem?

Thank you very much!

The header bytes are described as:

"FLXIMG:9999:XXXXXXXXXXX where: ... -'9999' are 4 size bytes indicating how long the new flash image is (how many bytes to read)"

Should these four size bytes be in big or little endian format? Neither of them seem to work on my setup, so I assume that I'm doing something else wrong, but I would like to eliminate this as an issue

The Bootloaders does not work with the 8MHz variant described here:
https://lowpowerlab.com/guide/moteino/moteino-8mhz/
Please drop a 8MHz variant of the bootloader here.
It would also be good to describe the Fuse settings in a formal way as document in github instead on various places in the forum or website.