Test HSE crystal circuit for best practice

Problem environment

The high frequency 32MHz crystal is calibrated through capacitor feet to ground, and plays a role in accurate radio transception.

Steps to reproduce

1. Refer to the schematic
2. Use a frequency counter
3. Measure the crystal circuit

Expected result

The output of the HSE crystal is as expected.

Actual result

HSE crystal output is unknown pending finding a suitable measurement tool.

Proposed method

1. Initiate a CW tone from SAMR34 with the help of Radio utility tool
2. SAMR34_SiP_Reference_Design_Package_V2.0/2. SAMR34_Reference_Design_Package/5. Radio Utility
3. Measure the frequency of the generated CW tone
4. Reduce the measured error between the measured frequency and the selected frequency
5. This could be done by tuning the external load capacitors of the crystal

Severity level

This is low priority because project requirements do not mandate calibration or radio service quality.

Frequency and capacitance was measured and correlated using a frequency counter, realtime oscilloscope, differential probes, and a spectrum analyser. It seems the HSE is much less sensitive and susceptible to interference compared with the LSE. The target frequencies (of both HSE and signal from SX1276) are obtained with 18pF load capacitors, as well as 12pF, 15pF, and 22pF substitutions.

Solved in 4e84bae and 8819d77.