I’ve done some experiments with the TinyLoRa library (GitHub - adafruit/TinyLoRa: LoRaWAN Library) on attiny85’s in the past. The attiny85 only has 8 kB of flash. The atmega328p of the UNO has 32 kB.
I’d encourage you to give the atmega328p (UNO) another chance! Benefits: Cheap, robust (no problems with 5 V), a lot less complicated than the SAMD21.
I’ve invested a lot of time getting to grips with the SAMD21. Lower level stuff you’d read in the datasheets is lot easier on the AVR chips (atmega328p) than on the SAMD21.
TinyLora is NoGo on V3.
This has been discussed on the Forum already.
Bad advice. RAM and Flash memory on ATmega328 and ATmega32u4 is just too limited for LoRaWAN compliant stacks if you want to use them with SPI LoRa modules. And as already said you will need level shifters for almost everything (LoRa module and most sensors are 3.3V nowadays). You should not use these MCU’s for new LoRaWAN development in combination with SPI LoRa modules where the LoRaWAN stack has to run on the MCU.
I have used logic level shifters, of the bought off eBay type, to connect a LoRa device to a 5V Arduino. On a scope the logic signals looked very marginal, so long term reliability could be doubtful.
I stand corrected. I was unaware about V3 and that it only seems to work with the LMIC library.
About ATmega328p robustness I have to clarify that my point was, that unlike most 3.3 V MCUs, 5 V won’t be critical to it.
I guess flash size wise the ATmega4809 might then be a suitable alternative. I don’t have experience with it. You can try to run the dev boards at 3.3 V or lower. Depending on the frequency the ATMega’s operate between 1.8 V and 5.5 V. It also comes in a DIP package.
The Seeeduino XIAO - Arduino Microcontroller - SAMD21 Cortex M0+ is also on back order - no stock! So still doesnt help with the question " Where are all the samd21 chips"
Unfortunately it has a couple of drawbacks: it’s available only in BGA packaging and there’s a significant amount of external RF circuitry required around the antenna.