cn0391.h

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/***************************************************************************/
 
#ifndef __CN0391_H__
#define __CN0391_H__
 
#include "ad7124.h"
#include "no_os_thermocouple.h"
#include "no_os_rtd.h"
 
#define CN0391_ADC_RESOLUTION   24  /* AD7124 is a high precision 24-bit Sigma-Delta ADC */
#define CN0391_ADC_FULL_SCALE   (1U << CN0391_ADC_RESOLUTION)  /* 2^24 */
#define CN0391_ADC_MIDSCALE (CN0391_ADC_FULL_SCALE >> 1)   /* 2^23, bipolar zero-code */
 
#define CN0391_GAIN         32
#define CN0391_RTD_GAIN         1
#define CN0391_THERMO_RES       1600
#define CN0391_ADC_REF_VOLTAGE      2.5
 
/* AD7124 setup indices */
#define CN0391_SETUP_TC_IDX     0   /* Thermocouple: Gain=32, bipolar, internal ref */
#define CN0391_SETUP_RTD_IDX        1   /* R5 + CJC RTD: Gain=1, bipolar, internal ref */
 
/* AD7124-8 internal oscillator frequency at full power mode (Hz) */
#define CN0391_ADC_CLK_HZ       614400ULL
/* Filter FS register value: sets output data rate = fCLK / (32 × FS) */
#define CN0391_FILTER_FS        384U
 
/*
 * Digital filter type selection.
 * Override at build time with -DCN0391_FILTER_TYPE=<value>:
 *   0 — Sinc4: best noise rejection, 4-period settling (default)
 *   2 — Sinc3: 25% faster settling, slightly lower noise rejection
 *
 * AD7124_FILT_REG_FILTER(CN0391_FILTER_TYPE) encodes this into the
 * filter register bits [23:21].
 *
 * NOTE: in single conversion mode (used by cn0391_read_temperature) the
 * AD7124 always runs the full 4-stage CIC filter for settling regardless
 * of this setting. Sinc3 vs Sinc4 therefore has no effect on acquisition
 * speed here; it only affects noise shaping of the output word. The only
 * effective knob for reducing conversion time in this mode is CN0391_FILTER_FS.
 */
#ifndef CN0391_FILTER_TYPE
#define CN0391_FILTER_TYPE      0   /* Sinc4 */
#endif
 
#if (CN0391_FILTER_TYPE == 0)
#define CN0391_FILTER_ORDER     4U  /* Sinc4: 4-period settling */
#elif (CN0391_FILTER_TYPE == 2)
#define CN0391_FILTER_ORDER     3U  /* Sinc3: 3-period settling */
#else
#error "CN0391_FILTER_TYPE must be 0 (Sinc4) or 2 (Sinc3)"
#endif
 
/*
 * Filter register value combining type, FS, and no post-filter.
 * Used to initialise all 8 AD7124 filter setup registers in common_data.c.
 */
#define CN0391_FILTER_REG_VAL \
    (AD7124_FILT_REG_FILTER(CN0391_FILTER_TYPE) | AD7124_FILT_REG_FS(CN0391_FILTER_FS))
 
/*
 * Worst-case time for one single conversion (µs).
 * SincN requires (filter_order + 1) conversion periods before producing a
 * valid output after a channel switch:
 *   t_conv = (filter_order + 1) × FS × 32 / fCLK
 */
#define CN0391_CONV_TIME_US \
    (((CN0391_FILTER_ORDER + 1U) * CN0391_FILTER_FS * 32ULL * 1000000ULL) \
     / CN0391_ADC_CLK_HZ)
 
/*
 * Minimum number of SPI STATUS register polls to cover one worst-case
 * conversion, with a 2× safety margin.
 * Each poll transfers 2 bytes (1 command + 1 STATUS data byte):
 *   poll_time_us = 2 × 8 / spi_hz × 1e6
 *   poll_cnt = conv_time_us × 2 / poll_time_us
 *            = conv_time_us × spi_hz / (8 × 1e6)
 */
#define CN0391_SPI_RDY_POLL_CNT(spi_hz) \
    ((CN0391_CONV_TIME_US * 2ULL * (spi_hz)) / (16ULL * 1000000ULL))
 
#define CN0391_ADC_CHANNELS_PER_IIO_CH  3
 
#define CN0391_NUM_IIO_CHANNELS     4
 
#define CN0391_CH0_ID           0
#define CN0391_CH1_ID           1
#define CN0391_CH2_ID           2
#define CN0391_CH3_ID           3
 
/* ADC channel triplet for one thermocouple IIO channel */
struct cn0391_adc_ch_map {
    uint8_t tc;       /* thermocouple ADC channel */
    uint8_t r5;       /* reference resistor R5 ADC channel */
    uint8_t rtd;     /* CJC RTD ADC channel */
    uint8_t iout_ain;   /* AIN pin index for IOUT0 excitation (IOUT_CH0 field) */
};
 
struct cn0391_cache {
    double hot_junction_temp;
    double cold_junction_temp;
    double tc_voltage;
    double rtd_resistance;
};
 
struct cn0391_dev {
    struct ad7124_dev *ad7124_dev;
    /* Cached last measurement per IIO channel; -1 = no valid cache */
    int8_t cache_ch;
    struct cn0391_cache cache;
};
 
struct cn0391_init_param {
    struct ad7124_init_param *ad7124_init;
};

int cn0391_init(struct cn0391_dev **dev,
        struct cn0391_init_param *init_param);

int cn0391_remove(struct cn0391_dev *dev);

int cn0391_read_temperature(struct cn0391_dev *dev, uint8_t ch_idx,
                double *hot_junction_temp,
                double *cold_junction_temp,
                double *thermocouple_voltage,
                double *rtd_resistance);
 
#endif /* __CN0391_H__ */