Finally, if the uploader on the PC side were to keep trying for at least 6 second, it would be guaranteed to succeed.
With a watchdog timeout of 5 seconds, and with the boot loader waiting at least one second for incoming upload-/reset-req’s, that means the board should be able to replace a faulty sketch at least 20% of the time. What this would do, is to keep the board entering USB serial mode every once in a while, even if the sketch crashes. * the serial USB driver continues to implement The Maple Trick
* each time, the boot loader will start and re-init USB serial, and wait for boot requests for some time * a stuck sketch will thus reset, maybe even periodically * we set up a watchdog and trigger it main, just after each call to loop() for example * when the sketch runs, it continues to use the boot loader’s USB driver
* on reset, the boot loader sets up USB serial This is one of the issues an all-serial-non-re-enumerating boot loader can solve, I hope – with the help of the IWDG watchdog: This may also imply that anyone using a different USB mode such as HID or MEM disk will run into this same issue. Yes, serial USB has to be running & attached for it to pick up a reset request (I’ll call it “The Maple Trick”). I’m reporting this here, though it touches on another thread, about having to call Serial.begin() in the sketch – viewtopic.php?f=3&t=703 If all of this is indeed the case, it could be a very interesting avenue to explore IMO, but for some reason there seems to be no recent development going on in this area, at least not any I could find. Lastly, the use of the Atmel STK protocol in this driver means that “avrdude” might be all that’s needed to upload firware. In particular, it looks like this approach avoids the need for any driver setup and config files on Windows, Mac OSX, and Linux, and that even pulsing D+ for a reattach may no longer be necessary, since the USB connection remains of the same type. The interesting bit is that this might avoid the DFU vs VCP (serial) complexity. Has anyone explored this serial-only USB boot loader, as alternative for the DFU approach?įurther developments, but still relatively old:
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