[LTD noup] drivers: sensor: add stm32f401x temperature driver

There is an issue with this driver.

At present, there's no good way for board-level
configuration (specifically, the voltages on the V_REF- and V_REF+
external pins, which are needed to convert ADC values to volts) to be
made available portably to drivers.

Hack around this here by hard-coding reasonable defaults of 0V for
V_REF- and 3.3V for V_REF+.

Signed-off-by: Marti Bolivar <marti.bolivar@linaro.org>

Author: Marti Bolivar

drivers/sensor/stm32/temp_stm32.h

@@ -0,0 +1,26 @@
+/*
+ * Copyright (c) 2017 Linaro Limited.
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#ifndef _STM32_TEMP_H_
+#define _STM32_TEMP_H_
+
+#include <stdint.h>
+
+#include <device.h>
+#include <soc.h>
+
+struct temp_stm32_config {
+	ADC_TypeDef *adc;
+	ADC_Common_TypeDef *adc_common;
+	u8_t adc_channel;
+	struct stm32_pclken pclken;
+};
+
+struct temp_stm32_data {
+	struct device *clock;
+};
+
+#endif	/* _STM32_TEMP_H_ */

drivers/sensor/stm32/temp_stm32f401x.c

@@ -15,22 +15,166 @@
  *          as 45 degrees C.
  */
 
-#include <device.h>
+#define SYS_LOG_DOMAIN "TEMPSTM32F401"
+#define SYS_LOG_LEVEL CONFIG_SYS_LOG_SENSOR_LEVEL
+
+#include <drivers/clock_control/stm32_clock_control.h>
+#include <errno.h>
+#include <logging/sys_log.h>
+#include <misc/__assert.h>
 #include <sensor.h>
 
-/* TODO */
+#include "temp_stm32.h"
+
+#define DEV_CFG(dev)							\
+	((const struct temp_stm32_config*)(dev)->config->config_info)
+#define DEV_DATA(dev) ((struct temp_stm32_data *)(dev)->driver_data)
+
+/*
+ * HACK: absent a better way to learn the analog voltage reference on
+ * the board we are running on, hard-code V_REF+ to 3.3V, and assume
+ * V_REF- = 0V.
+ */
+#define VREF_MILLIVOLTS 3300
+#define VREF_VOLTS ((float)VREF_MILLIVOLTS / 1000.0f)
+
+/*
+ * See STM32F401xD, STM32F401xE datasheet 6.3.21 and chip
+ * reference manual and ST RM0368 chapter 11.
+ */
+#define STM32F401_V25		0.76f	/* volts */
+#define STM32F401_AVG_SLOPE	0.0025f /* volts / (degree C) */
+
+#define ADC_RESOLUTION_12BIT 0x00
+#define ADC_TO_VOLTS(adc_val) ((float)(adc_val) * VREF_VOLTS / 4095.0f)
+#define ADC_PRESCALER_PCLK_DIV_8 0x03
+#define ADC_SAMPLE_480_CYCLES 0x07
+#define ADC_ONE_CONVERSION 0x00
+
+/* This is valid for STM32F401x. */
+#define ADC_TEMP_CHANNEL 18
+#define ADC_TEMP_SMPR(adc) (adc)->SMPR1
+#define ADC_TEMP_SMPR_SMP ADC_SMPR1_SMP18
+#define ADC_TEMP_SMPR_POS ADC_SMPR1_SMP18_Pos
+
 static int temp_stm32f401x_sample_fetch(struct device *dev,
 					enum sensor_channel chan)
 {
+	const struct temp_stm32_config *cfg = DEV_CFG(dev);
+	ADC_TypeDef *adc = cfg->adc;
+	u32_t tmp;
+
+	__ASSERT(cfg->adc_channel == ADC_TEMP_CHANNEL,
+		 "Expected temperature sensor channel %d", ADC_TEMP_CHANNEL);
+
+	/*
+	 * Configure ADC for polled conversion of temperature sensor.
+	 *
+	 * TODO: this configuration could be improved (timing, etc.).
+	 */
+
+	/*
+	 * CR1:
+	 *
+	 * - 12 bit resolution (the maximum).
+	 *
+	 * - Software initiated, polled conversion only (no
+	 *   interrupts, injected groups, scan mode, etc.).
+	 */
+
+	tmp = adc->CR1;
+	tmp &= ~(ADC_CR1_RES | ADC_CR1_JDISCEN | ADC_CR1_DISCEN |
+		 ADC_CR1_JAUTO | ADC_CR1_SCAN | ADC_CR1_JEOCIE |
+		 ADC_CR1_AWDIE | ADC_CR1_EOCIE);
+	tmp |= (ADC_RESOLUTION_12BIT << ADC_CR1_RES_Pos);
+	adc->CR1 = tmp;
+
+	/*
+	 * CR2:
+	 *
+	 * - Software initiated, polled conversion of a single channel
+	 *   only (no external triggers, DMA, continuous conversion).
+	 *
+	 * - Right-aligned data in DR.
+	 *
+	 * - EOC bit in SR should be set at end of conversion.
+	 */
+
+	adc->CR2 &= ~(ADC_CR2_EXTEN | ADC_CR2_JEXTEN | ADC_CR2_ALIGN |
+		      ADC_CR2_EOCS | ADC_CR2_DDS | ADC_CR2_DMA |
+		      ADC_CR2_CONT);
+
+	/*
+	 * SMPR:
+	 *
+	 * Temperature sensor sample time is 480 ADC cycles (the
+	 * maximum).
+	 */
+
+	tmp = ADC_TEMP_SMPR(adc);
+	tmp &= ~ADC_TEMP_SMPR_SMP;
+	tmp |= (ADC_SAMPLE_480_CYCLES << ADC_TEMP_SMPR_POS);
+	ADC_TEMP_SMPR(adc) = tmp;
+
+	/*
+	 * SQRx: Convert channel. One channel is being converted.
+	 */
+
+	tmp = adc->SQR3;
+	tmp &= ~ADC_SQR3_SQ1;
+	tmp |= (ADC_TEMP_CHANNEL << ADC_SQR3_SQ1_Pos);
+	adc->SQR3 = tmp;
+
+	tmp = adc->SQR1;
+	tmp &= ~ADC_SQR1_L;
+	tmp |= (ADC_ONE_CONVERSION << ADC_SQR1_L_Pos);
+	adc->SQR1 = tmp;
+
+	/*
+	 * Start the ADC conversion, and wait for it to complete.
+	 */
+
+	adc->SR = ~(ADC_SR_EOC | ADC_SR_STRT);
+	adc->CR2 |= ADC_CR2_SWSTART;
+
+	do {
+	} while (!(adc->SR & ADC_SR_EOC));
+	adc->SR = ~(ADC_SR_EOC | ADC_SR_STRT);
+
 	return 0;
 }
 
-/* TODO */
+static inline float stm32f401x_temp_c(float v_sense)
+{
+	/*
+	 * The voltage read by the temperature sensor, v_sense, is a
+	 * linear function of the temperature. The point-slope form of
+	 * the line is:
+	 *
+	 * (Temperature - 25.0°C) * Avg_Slope = v_sense - V_25
+	 *
+	 * Where V_25 is the measured voltage at 25°C, and Avg_Slope
+	 * is the slope of the line in V/°C.
+	 *
+	 * Use this formula to convert the voltage to a
+	 * temperature. See ST RM0368 11.9 and the chip datasheet for
+	 * more details.
+	 */
+	return ((v_sense - STM32F401_V25) / STM32F401_AVG_SLOPE + 25.0f);
+}
+
 static int temp_stm32f401x_channel_get(struct device *dev,
 				       enum sensor_channel chan,
 				       struct sensor_value *val)
 {
-	val->val1 = 0;
+	const struct temp_stm32_config *cfg = DEV_CFG(dev);
+	ADC_TypeDef *adc = cfg->adc;
+	u32_t adc_dr = adc->DR;
+	float v_sense = ADC_TO_VOLTS(adc_dr);
+	float deg_c = stm32f401x_temp_c(v_sense);
+
+	/* TODO fractional part */
+	val->val1 = (int32_t)deg_c;
 	val->val2 = 0;
 	return 0;
 }
@@ -40,12 +184,59 @@ static const struct sensor_driver_api temp_stm32f401x_driver_api = {
 	.channel_get = temp_stm32f401x_channel_get,
 };
 
-/* TODO */
+static inline void __temp_stm32f401x_get_clock(struct device *dev)
+{
+	struct temp_stm32_data *data = DEV_DATA(dev);
+	struct device *clk = device_get_binding(STM32_CLOCK_CONTROL_NAME);
+
+	__ASSERT_NO_MSG(clk);
+	data->clock = clk;
+}
+
 static int temp_stm32f401x_init(struct device *dev)
 {
+	const struct temp_stm32_config *cfg = DEV_CFG(dev);
+	struct temp_stm32_data *data = DEV_DATA(dev);
+	ADC_TypeDef *adc = cfg->adc;
+	ADC_Common_TypeDef *adc_common = cfg->adc_common;
+	u32_t tmp;
+
+	/* Turn on digital clock. */
+        __temp_stm32f401x_get_clock(dev);
+	clock_control_on(data->clock,
+			 (clock_control_subsys_t*)&cfg->pclken);
+
+	/* Turn on ADC. */
+	adc->CR2 |= ADC_CR2_ADON;
+
+	/* ADC configuration for temperature sensor.
+	 *
+	 * - ADC clock prescaler to slowest possible (HACK) to avoid
+	 *   reading data sheets to figure out fastest possible.
+	 *
+	 * - Select temperature sensor, deselect VBAT (they are
+	 *   mutually exclusive, and VBAT has precedence).
+	 */
+	tmp = adc_common->CCR;
+	tmp &= ~(ADC_CCR_VBATE | ADC_CCR_ADCPRE);
+	tmp |= ((ADC_PRESCALER_PCLK_DIV_8 << ADC_CCR_ADCPRE_Pos) |
+		ADC_CCR_TSVREFE);
+	adc_common->CCR = tmp;
+
 	return 0;
 }
 
+static struct temp_stm32_config temp_stm32f401x_config = {
+	.adc = ADC1,
+	.adc_common = ADC,
+	.adc_channel = ADC_TEMP_CHANNEL,
+	.pclken = { .bus = STM32_CLOCK_BUS_APB2,
+		    .enr = LL_APB2_GRP1_PERIPH_ADC1 },
+};
+
+static struct temp_stm32_data temp_stm32f401x_data;
+
 DEVICE_AND_API_INIT(temp_stm32f401x, CONFIG_TEMP_STM32F401X_NAME,
-		    temp_stm32f401x_init, NULL, NULL, POST_KERNEL,
+		    temp_stm32f401x_init, &temp_stm32f401x_data,
+		    &temp_stm32f401x_config, POST_KERNEL,
 		    CONFIG_SENSOR_INIT_PRIORITY, &temp_stm32f401x_driver_api);