Setting up picture
I have seen a few comments about how to plug in the LoPy and update it. here is a picture of said setup. G28 to 3.3V. Worked for me!
I read somewhere that because the device does not have a built-in USB peripheral, like the original Pyboard does, that updating via USB was not possible.
The ESP32 chip has a built-in ROM bootloader that allows (among other things) to write to the external SPI flash via UART/serial. You could flash it using a serial cable/RS232 <-> uart converter instead of USB. You could also flash the ESP32 using another micro-controller, though you'd have to program the protocol yourself first. This ROM bootloader is automatically trigger at reset if GPIO0 / P2 / G23 is pulled low (connected to GND) during hardware reset.
You mention a bug- does that mean I have flashed a bad bootloader into my devices?
The bootloader that was shipped has a bug, the latest update via serial port fixes this bug. This bootloader can only be updated via serial connection.
It would also be nice to be able to trigger the device into its various update modes by a command over the wifi or the serial port.
I don't think the ROM bootloader can be triggered during normal operation.
Thank you- I did not realize that. In fact, I did not know it was possible to update the firmware via the serial port! I thought I read somewhere that because the device does not have a built-in USB peripheral, like the original Pyboard does, that updating via USB was not possible. So I have learned something important!
You mention a bug- does that mean I have flashed a bad bootloader into my devices? What does that mean for updating in the future?
It would also be nice to be able to trigger the device into its various update modes by a command over the wifi or the serial port. I understand that it is critical to have the "jumper" method for when the device is unresponsive over the wifi or serial. But for deployed devices, which might be hard to access, it would be nice to leave them in the AP mode, and walk (or drive) up with a notebook and connect to do the update.
Actually all the latest Firmware updates through serial port need a connection between GND and G23 on the expansion board to put the board into bootloader mode.
The connection between 3.3V and G28 is for safeboot mode / Wifi based updates which only flashes the firmware but not the bootloader. Since the stock bootloader has a bug it is highly recommended to update via the latest serial based updater available on the download page.