Is it possible to use HSI instead of HSE for the Sigfox Stack @B-L072Z-LRWAN1 devKIT?

[Jan Belohoubek]

We use B-L072Z-LRWAN1 (Murata TypeABZ) dev board, where we were able to set-up clock sources to use HSI (@32MHz with PLL - HW_SetHSEasSysClock(void)) instead of HSE during Sigfox transmission. From the firmware perspective, everything is fine, but we were unable to receive data (Sigfox infrastructure), while the same HW with HSE is OK.

As the sigfox stack is closed, we don't know if we can do more...

What is the reason behind HSE usage? Is it the hard-requirement, or not? Is it possible to set-up HSI somehow?

[Jan Belohoubek · Accepted solution]

STM's support answer to our question above was:

• there is the need for precision clock source (TCXO) both for TRX and MCU to fulfill Sigfox RF certification requirements because of narrow band modulation (uplink: 100bit/s, 100Hz sub band).
• both MCU and Radio must use the same clock source - explicit synchronization is required