On CC26X2, switching to the regular XOSC_HF involves requesting the XOSC in hardware and waiting until an interrupt says it is ready to go.

The correct way to switch to TCXO:

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1. Set TCXO_MODE and TCXO_MODE_XOSC_HF_EN
2. Wait 10us for bias to ramp up
3. Enable TCXO by setting DIO high
4. Wait 2ms for TCXO to stabilize
5. Set XOSC_HF_BYPASS to enable clock qualification
6. Set SCLK_HF_SRC_SEL to request clock switch

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Using the incorrect procedure was causing instability and unpredictable lockups at the edges of our temperature range.