From 57f6081960cd0425b7956c0e246ddaf8826e2682 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Joakim=20Nohlg=C3=A5rd?= <joakim.nohlgard@eistec.se>
Date: Fri, 16 Feb 2018 13:12:28 +0100
Subject: [PATCH] sys/analog_util: Refactor adc_map, fix compilation
Change the API to use int32_t instead of int, to allow for greater
flexibility on 8- and 16-bit platforms. Removed limitation on input
arguments that min < max. Times where it can be useful to have min > max
is when measuring a sensor where a higher measured voltage means a lower
physical value. For example a thermistor can be connected so that the
measured voltage goes down when the temperature goes up.
---
sys/analog_util/adc_util.c | 55 +++++++++++++++++++++++++++++---------
sys/include/analog_util.h | 5 ++--
2 files changed, 45 insertions(+), 15 deletions(-)
diff --git a/sys/analog_util/adc_util.c b/sys/analog_util/adc_util.c
index af4f480237..ba1ca7c9c4 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 UniversitÃĪt 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 NohlgÃĨrd <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 a23eee392f..b3aa408286 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
--
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