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[nrf fromlist] soc: nordic: nrf54l: Clean up internal capacitance calculations #2848

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[nrf fromlist] soc: nordic: nrf54l: Clean up internal capacitance calculations #2848

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7a68014
[nrf fromtree] soc: nrf54l: fix LFXO INTCAP calculation formula
gmarull Mar 14, 2025
e86fd6b
[nrf fromlist] soc: nordic: nrf54l: Clean up internal capacitance cal…
mstasiaknordic May 9, 2025
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73 changes: 33 additions & 40 deletions soc/nordic/nrf54l/soc.c
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Original file line number Diff line number Diff line change
Expand Up @@ -17,7 +17,6 @@

#include <zephyr/devicetree.h>
#include <zephyr/kernel.h>
#include <zephyr/devicetree.h>
#include <zephyr/init.h>
#include <zephyr/logging/log.h>
#include <zephyr/cache.h>
Expand Down Expand Up @@ -50,46 +49,43 @@ static inline void power_and_clock_configuration(void)
*/
#if DT_ENUM_HAS_VALUE(LFXO_NODE, load_capacitors, internal)
uint32_t xosc32ktrim = NRF_FICR->XOSC32KTRIM;

uint32_t offset_k =
(xosc32ktrim & FICR_XOSC32KTRIM_OFFSET_Msk) >> FICR_XOSC32KTRIM_OFFSET_Pos;

/* The SLOPE field is in the two's complement form, hence this special
* handling. Ideally, it would result in just one SBFX instruction for
* extracting the slope value, at least gcc is capable of producing such
* output, but since the compiler apparently tries first to optimize
* additions and subtractions, it generates slightly less than optimal
* code.
*/
uint32_t slope_field_k =
(xosc32ktrim & FICR_XOSC32KTRIM_SLOPE_Msk) >> FICR_XOSC32KTRIM_SLOPE_Pos;
uint32_t slope_mask_k = FICR_XOSC32KTRIM_SLOPE_Msk >> FICR_XOSC32KTRIM_SLOPE_Pos;
uint32_t slope_sign_k = (slope_mask_k - (slope_mask_k >> 1));
int32_t slope_k = (int32_t)(slope_field_k ^ slope_sign_k) - (int32_t)slope_sign_k;

uint32_t offset_k =
(xosc32ktrim & FICR_XOSC32KTRIM_OFFSET_Msk) >> FICR_XOSC32KTRIM_OFFSET_Pos;
/* As specified in the nRF54L15 PS:
* CAPVALUE = round( (CAPACITANCE - 4) * (FICR->XOSC32KTRIM.SLOPE + 0.765625 * 2^9)/(2^9)
* CAPVALUE = round( (2*CAPACITANCE - 12) * (FICR->XOSC32KTRIM.SLOPE + 0.765625 * 2^9)/(2^9)
* + FICR->XOSC32KTRIM.OFFSET/(2^6) );
* where CAPACITANCE is the desired capacitor value in pF, holding any
* value between 4 pF and 18 pF in 0.5 pF steps.
*/

/* Encoding of desired capacitance (single ended) to value required for INTCAP core
* calculation: (CAP_VAL - 4 pF)* 0.5
* That translate to ((CAP_VAL_FEMTO_F - 4000fF) * 2UL) / 1000UL
*
* NOTE: The desired capacitance value is used in encoded from in INTCAP calculation formula
* That is different than in case of HFXO.
*/
uint32_t cap_val_encoded = (((DT_PROP(LFXO_NODE, load_capacitance_femtofarad) - 4000UL)
* 2UL) / 1000UL);
uint32_t lfxo_intcap_femto_f = DT_PROP(LFXO_NODE, load_capacitance_femtofarad);

/* Calculation of INTCAP code before rounding. Min that calculations here are done on
* values multiplied by 2^9, e.g. 0.765625 * 2^9 = 392.
* offset_k should be divided by 2^6, but to add it to value shifted by 2^9 we have to
* multiply it be 2^3.
* multiply it be 2^3. Capacitance value passed to the formula is in femto Farads to
* avoid floating point data type. Hence, offset_k needs to be multiplied by 1000.
*/
uint32_t mid_val = (cap_val_encoded - 4UL) * (uint32_t)(slope_k + 392UL)
+ (offset_k << 3UL);
uint32_t lfxo_intcap_mid_val = (2UL * lfxo_intcap_femto_f - 12000UL)
* (uint32_t)(slope_k + 392UL) + (offset_k << 3UL) * 1000UL;

/* Get integer part of the INTCAP code */
uint32_t lfxo_intcap = mid_val >> 9UL;
/* Get integer part of the INTCAP by dividing by 2^9 and convert to pico Farads. */
uint32_t lfxo_intcap = lfxo_intcap_mid_val / 512000UL;

/* Round based on fractional part */
if ((mid_val & BIT_MASK(9)) > (BIT_MASK(9) / 2)) {
/* Round based on fractional part. */
if (lfxo_intcap_mid_val % 512000UL >= 256000UL) {
lfxo_intcap++;
}

Expand All @@ -107,11 +103,11 @@ static inline void power_and_clock_configuration(void)
* additions and subtractions, it generates slightly less than optimal
* code.
*/
uint32_t slope_field =
uint32_t slope_field_m =
(xosc32mtrim & FICR_XOSC32MTRIM_SLOPE_Msk) >> FICR_XOSC32MTRIM_SLOPE_Pos;
uint32_t slope_mask = FICR_XOSC32MTRIM_SLOPE_Msk >> FICR_XOSC32MTRIM_SLOPE_Pos;
uint32_t slope_sign = (slope_mask - (slope_mask >> 1));
int32_t slope_m = (int32_t)(slope_field ^ slope_sign) - (int32_t)slope_sign;
uint32_t slope_mask_m = FICR_XOSC32MTRIM_SLOPE_Msk >> FICR_XOSC32MTRIM_SLOPE_Pos;
uint32_t slope_sign_m = (slope_mask_m - (slope_mask_m >> 1));
int32_t slope_m = (int32_t)(slope_field_m ^ slope_sign_m) - (int32_t)slope_sign_m;
uint32_t offset_m =
(xosc32mtrim & FICR_XOSC32MTRIM_OFFSET_Msk) >> FICR_XOSC32MTRIM_OFFSET_Pos;
/* As specified in the nRF54L15 PS:
Expand All @@ -121,22 +117,19 @@ static inline void power_and_clock_configuration(void)
* holding any value between 4.0 pF and 17.0 pF in 0.25 pF steps.
*/

/* NOTE 1: Requested HFXO internal capacitance in femto Faradas is used directly in formula
* to calculate INTCAP code. That is different than in case of LFXO.
*
* NOTE 2: PS formula uses piko Farads, the implementation of the formula uses femto Farads
* to avoid use of floating point data type.
*/
uint32_t cap_val_femto_f = DT_PROP(HFXO_NODE, load_capacitance_femtofarad);
uint32_t hfxo_intcap_femto_f = DT_PROP(HFXO_NODE, load_capacitance_femtofarad);

uint32_t mid_val_intcap = (((cap_val_femto_f - 5500UL) * (uint32_t)(slope_m + 791UL))
+ (offset_m << 2UL) * 1000UL) >> 8UL;
/* Capacitance value passed to the formula is in femto Farads to
* avoid floating point data type. Hence, offset_m needs to be multiplied by 1000.
*/
uint32_t hfxo_intcap_mid_val = (((hfxo_intcap_femto_f - 5500UL)
* (uint32_t)(slope_m + 791UL)) + (offset_m << 2UL) * 1000UL) >> 8UL;

/* Convert the calculated value to piko Farads */
uint32_t hfxo_intcap = mid_val_intcap / 1000;
/* Convert the calculated value to piko Farads. */
uint32_t hfxo_intcap = hfxo_intcap_mid_val / 1000;

/* Round based on fractional part */
if (mid_val_intcap % 1000 >= 500) {
/* Round based on fractional part. */
if (hfxo_intcap_mid_val % 1000 >= 500) {
hfxo_intcap++;
}

Expand Down