diff --git a/sys/analog_util/adc_util.c b/sys/analog_util/adc_util.c index af4f480237b2d8a42cf01ab7fad41e1129e12260..ba1ca7c9c40b0f65eec3b6073d8431cfab3e4b88 100644 --- a/sys/analog_util/adc_util.c +++ b/sys/analog_util/adc_util.c @@ -1,4 +1,5 @@ /* + * Copyright (C) 2018 Eistec AB * Copyright (C) 2015 Freie Universität Berlin * * This file is subject to the terms and conditions of the GNU Lesser @@ -14,28 +15,58 @@ * @brief ADC utility function implementation * * @author Hauke Petersen <hauke.petersen@fu-berlin.de> + * @author Joakim Nohlgård <joakim.nohlgard@eistec.se> * * @} */ +#include <stdint.h> +#include <inttypes.h> + +#include "cpu.h" +#include "periph/adc.h" #include "analog_util.h" +#include "assert.h" + +#define ENABLE_DEBUG (0) +#include "debug.h" -/* keep a max value to ADC resolution mapping for quick access in the ROM */ -static const int val_max[] = { - [ADC_RES_6BIT] = 0x003f, - [ADC_RES_8BIT] = 0x00ff, - [ADC_RES_10BIT] = 0x03ff, - [ADC_RES_12BIT] = 0x0fff, - [ADC_RES_14BIT] = 0x3fff, - [ADC_RES_16BIT] = 0xffff -}; +/** + * @brief Convert adc_res_t resolution setting into numeric bit count + */ +static unsigned int _adc_res_bits(adc_res_t res) +{ + switch (res) { + case ADC_RES_6BIT: + return 6; + case ADC_RES_8BIT: + return 8; + case ADC_RES_10BIT: + return 10; + case ADC_RES_12BIT: + return 12; + case ADC_RES_14BIT: + return 14; + case ADC_RES_16BIT: + return 16; + default: + /* Unsupported ADC resolution, modify your application to use a + * different resolution, or add it above */ + assert(0 == 1); + return 0; + } +} -int adc_util_map(int sample, adc_res_t res, int min, int max) +int32_t adc_util_map(int sample, adc_res_t res, int32_t min, int32_t max) { - return ((((max - min) * sample) / val_max[res]) + min); + /* Using 64 bit signed int as intermediate to prevent overflow when range + * multiplied by sample requires more than 32 bits */ + int32_t scaled = (((int64_t)(max - min) * sample) >> _adc_res_bits(res)); + DEBUG("scaled: %" PRId32 "\n", scaled); + return (min + scaled); } float adc_util_mapf(int sample, adc_res_t res, float min, float max) { - return ((((max - min) * sample) / val_max[res]) + min); + return ((((max - min) * sample) / ((int32_t)1L << _adc_res_bits(res))) + min); } diff --git a/sys/include/analog_util.h b/sys/include/analog_util.h index a23eee392f97f3c6bfdc88055e0f03a4a5bff28c..b3aa408286e11063a18531c38820734f12810f7e 100644 --- a/sys/include/analog_util.h +++ b/sys/include/analog_util.h @@ -22,6 +22,7 @@ #define ANALOG_UTIL_H #include <stdint.h> + #include "periph/adc.h" #ifdef __cplusplus @@ -34,8 +35,6 @@ extern "C" { * This function is useful for converting sampled ADC values into their physical * representation. * - * The min value is asserted to be smaller than the max value. - * * @param[in] sample sampled ADC value * @param[in] res ADC resolution * @param[in] min the lower bound of the target interval @@ -43,7 +42,7 @@ extern "C" { * * @return the mapped value */ -int adc_util_map(int sample, adc_res_t res, int min, int max); +int32_t adc_util_map(int sample, adc_res_t res, int32_t min, int32_t max); /** * @brief Map a sampled ADC value to a given range (using floating point