Port LMIC to other controller without Arduino

[Muecke1978]

Hy there,
we are about to start our own LoRa project using a TI ARM processor and an SX1276. In earlier projects we have used Murata ABZ module.
What would be your recommended approach to implement LoRa stack and SX1276 driver? Port this repository to our platform? How much Arduino dependencies will we be facing? Any of them difficult to overcome?
Our system holds a ARM Cortex M3 with about 64k Flash available, running TI RTOS. Do we have a chance to get LoRa running on this? Can you estimate system requirements (Flash, RAM, CPU)?
Any help appreciated
Harald

[terrillmoore]

This will work. We ported to a RISC-V outside the Ardiuno environment. You have to recode hal.cpp, and you have to deal carefully with timing. No changes were made to the core LMIC at all; it has no Arduino dependencies. The makefiles built the lmic directory, but provided our own hal.cpp equivalent which was outside the tree. Size will be identical to the size on an M0. Turn off class B support (BEACON and PING) and you'll minimize the footprint. I didn't publish that code, because it was for the RISC-V FPGA that MCCI did with a customer, and it never went to production. That was a 6 MHz CPU, and things worked fine. It was the uncompressed RISC instruction set so code density is about 50% of Thumb code, and it still fit in 64k with an app.

If you read the IBM documentation, they discuss a little about what's needed from the HAL.

Best regards,
--Terry

[manuelbl]

For an example, see https://github.com/manuelbl/ttn-esp32. It's a port to ESP-IDF, Espressif's RTOS for ESP32 MCU. To make easy to use, LMIC is run in a separate task so users don't need to be careful about timing.

[Coimbra1984]

Hi,
I'm currently working on the porting as described above. I have one question. Our os needs to run with an os tick of 10us. If I understand your port correctly, you differ between LMIC tick (16us) and ESP32 tick (1us). I can probably set the LMIC tick to 20us in my case and than convert between both "worlds". I just have to correctly implement hal_ticks() -> return ticks in LMIC units and hal_waitUntil -> convert LMIC time parameter to my internal time. Did I understand that correctly?

[terrillmoore]

Maybe. It would be better to look at the comments for how the time works. Look in oslmic.h for how the conversions are defined and restricted. The arduino > LMIC conversions are quite convoluted and fragile, because the code is trying to deal with the fact that micros() wraps around after 2^32 microseconds, but the LMIC ticks must wrap around after 2^36 microseconds (2^32 ticks). If you have a 64-bit high-res counter, you can simply shift it around and have a much simpler and more robust time base.