SWCU195A December 2024 – May 2025 CC2744R7-Q1 , CC2745P10-Q1 , CC2745R10-Q1 , CC2745R7-Q1 , CC2755R10
HFOSC (internal RC oscillator) is tracked using HFXT (External crystal oscillator)
To enable this tracking loop, the following MMRs must be set:
CKMD.HFTRACKCTL.EN
CKMD.HFXTCTL.EN
The Tracking loop ratio is adjusted using CKMD.HFTRACKCTL.RATIO MMR.
The ratio is of the format 2b.24b. That is, there are 24 fractional bits.
HFTRACKCTL.RATIO = [(ull_freq)/(2*HFXT freq)]*2^24 = [24/2*48]*2^24 = 0x400000
Multiply by 2^24 because we want to shift the decimal by 24 bits, as the ratio format is 2.24b.
The KI and KP value of the loop filter is adjusted using the MMR CKMD.LOOPCFG.
The filter is designed to achieve <100ppm in ~250μs and <1ppm in ~1s.