失眠网 > 嵌入式Linux设备驱动程序开发指南18（IIO子系统(二)具有硬件触发功能的IIO子系统ADC模

嵌入式Linux设备驱动程序开发指南18（IIO子系统(二)具有硬件触发功能的IIO子系统ADC模

时间：2024-06-14 01:00:18

IIO子系统二具有硬件触发功能的IIO子系统ADC模块

十八、IIO子系统(二) 具有硬件触发功能的IIO子系统ADC模块18.1 简介18.2 设备树18.3 硬件触发驱动功能分析18.3.1 睡眠和唤醒18.3.2 中断管理18.4 带睡眠的硬件触发ADC代码18.5 应用代码18.6 调试

十八、IIO子系统(二) 具有硬件触发功能的IIO子系统ADC模块

18.1 简介

由于17章没有介绍完IIO子系统，本章继续介绍具备硬件触发功能的IIO子系统的ADC模块，ADC转换由硬件触发器启动。将使用按键产生重大触发ADC转换，还需要一个等待队列在进程和中断上下文之间进行同步。

每当按下按键时，产生重大将唤醒用户进程，驱动的读回调函数会把ADC值发送到用户。

18.2 设备树

连接按键的GPIO引脚增加一个int-gpio属性，还需要增加一个pinctrl-0属性，该属性指向一个引脚配置节点，用于将处理器的一个引脚复用为GPIO，将引脚方向设置为输入，并获取引脚对应的Linux中断号。reg属性值是片选信号的CS值。

spi3: spi@400 {compatible = "atmel,at91rm9200-spi";reg = <0x400 0x200>;interrupts = <23 IRQ_TYPE_LEVEL_HIGH 7>;clocks = <&flx4_clk>;clock-names = "spi_clk";#address-cells = <1>;#size-cells = <0>;pinctrl-names = "default";pinctrl-0 = <&pinctrl_mikrobus_spi &pinctrl_mikrobus1_spi_cs &pinctrl_mikrobus2_spi_cs>;atmel,fifo-size = <16>;status = "okay"; /* Conflict with uart6 and i2c3. *//* ADC: ltc2422@0 {compatible = "arrow,ltc2422";spi-max-frequency = <2000000>;reg = <0>;pinctrl-0 = <&pinctrl_key_gpio_default>;int-gpios = <&pioA PIN_PA29 GPIO_ACTIVE_LOW>;interrupt-parent = <&pioA>;interrupts = <29 IRQ_TYPE_EDGE_FALLING>;}; */};

18.3 硬件触发驱动功能分析

18.3.1 睡眠和唤醒

睡眠和唤醒主要步骤：

1、linux定义的等待队列定义了wait_queue_head_t结构来管理，如下：

linux/linux/wait.h

定义结构如下：

struct ADC_data {struct gpio_desc *gpio;int irq;wait_queue_head_twq_data_available;struct spi_device *spi;u8 buffer[4];boolconversion_done;struct mutexlock;};

在probe()函数进行动态初始化。

用户进程设置睡眠状态，它会假设将来某些条件会变成真。在Linux内核中最简单的一种睡眠方法是调用wait_event宏，它将处理睡眠细节和检查进程等待条件结合在一起。你将在驱动ltc2422_read_raw()函数里调用，如下：

wait_event_interruptible(st->wq_data_available, st->conversion_done); //变体

只有中断处理程序通知ADC转换开始，即条件为真，wait_event_interruptible才会去唤醒进程。

你将在中断处理函数中唤醒进程，如下：

static irqreturn_t ltc2422_adc_interrupt(int irq, void *data){static unsigned long last;unsigned long now;struct ADC_data *st = data;now = jiffies;if ((now - last) < (HZ/10))return IRQ_HANDLED;last = now;st->conversion_done = true;wake_up_interruptible(&st->wq_data_available);return IRQ_HANDLED;}

18.3.2 中断管理

在probe()函数里，将使用以下函数获取int-gpio属性中的GPIO描述符，如下；

devm_gpiod_get_index(&spi->dev, LTC2422_GPIO_NAME, 0, GPIOD_IN);

然后将描述符参数传递给以下函数，来获取Linux中断号，如下：

gpiod_to_irq(st->gpio);

申请中断号函数，如下：

devm_request_irq(&spi->dev, st->irq, ltc2422_adc_interrupt,IRQF_TRIGGER_FALLING, id->name, st); //st是私有数据指针

18.4 带睡眠的硬件触发ADC代码

#include <linux/module.h>#include <linux/spi/spi.h>#include <linux/interrupt.h>#include <linux/of_gpio.h>#include <linux/iio/iio.h>#include <linux/wait.h>#define LTC2422_GPIO_NAME"int"struct ADC_data {struct gpio_desc *gpio;int irq;wait_queue_head_twq_data_available;struct spi_device *spi;u8 buffer[4];boolconversion_done;struct mutexlock;};static irqreturn_t ltc2422_adc_interrupt(int irq, void *data){static unsigned long last;unsigned long now;struct ADC_data *st = data;now = jiffies;if ((now - last) < (HZ/10))return IRQ_HANDLED;last = now;st->conversion_done = true;wake_up_interruptible(&st->wq_data_available);return IRQ_HANDLED;}static const struct iio_chan_spec ltc2422_channel[] = {{.type= IIO_VOLTAGE,.indexed= 1,.output= 1,.channel= 0,.info_mask_separate = BIT(IIO_CHAN_INFO_RAW),}};static int ltc2422_read_raw(struct iio_dev *indio_dev,struct iio_chan_spec const *chan, int *val, int *val2, long m){int ret;struct ADC_data *st = iio_priv(indio_dev);dev_info(&st->spi->dev, "Press PB_USER key to start conversion\n");switch (m) {case IIO_CHAN_INFO_RAW:mutex_lock(&st->lock);ret = wait_event_interruptible(st->wq_data_available, st->conversion_done);if (ret) {dev_err(&st->spi->dev, "Failed to request interrupt\n");return ret;}spi_read(st->spi, &st->buffer, 3);*val = st->buffer[0] << 16;*val |= st->buffer[1] << 8;*val |= st->buffer[2];st->conversion_done = false;mutex_unlock(&st->lock);return IIO_VAL_INT;default:break;}return -EINVAL;}static const struct iio_info ltc2422_info = {.read_raw = &ltc2422_read_raw,.driver_module = THIS_MODULE,};static int ltc2422_probe(struct spi_device *spi){struct iio_dev *indio_dev;struct ADC_data *st;int ret;dev_info(&spi->dev, "my_probe() function is called.\n");/* get the id from the driver structure to use the name */const struct spi_device_id *id = spi_get_device_id(spi);indio_dev = devm_iio_device_alloc(&spi->dev, sizeof(*st));if (indio_dev == NULL)return -ENOMEM;st = iio_priv(indio_dev); st->spi = spi;spi_set_drvdata(spi, indio_dev);/* * you can also use* devm_gpiod_get(&spi->dev, LTC2422_GPIO_NAME, GPIOD_IN);*/st->gpio = devm_gpiod_get_index(&spi->dev, LTC2422_GPIO_NAME, 0, GPIOD_IN);if (IS_ERR(st->gpio)) {dev_err(&spi->dev, "gpio get index failed\n");return PTR_ERR(st->gpio);}st->irq = gpiod_to_irq(st->gpio);if (st->irq < 0)return st->irq;dev_info(&spi->dev, "The IRQ number is: %d\n", st->irq);indio_dev->dev.parent = &spi->dev;indio_dev->channels = ltc2422_channel;indio_dev->info = &ltc2422_info;indio_dev->name = id->name;indio_dev->num_channels = 1;indio_dev->modes = INDIO_DIRECT_MODE;init_waitqueue_head(&st->wq_data_available);mutex_init(&st->lock);ret = devm_request_irq(&spi->dev, st->irq, ltc2422_adc_interrupt,IRQF_TRIGGER_FALLING, id->name, st);if (ret) {dev_err(&spi->dev, "failed to request interrupt %d (%d)", st->irq, ret);return ret;}ret = devm_iio_device_register(&spi->dev, indio_dev);if (ret < 0)return ret;st->conversion_done = false;return 0;}static int ltc2422_remove(struct spi_device *spi){dev_info(&spi->dev, "my_remove() function is called.\n");return 0;}static const struct of_device_id ltc2422_dt_ids[] = {{.compatible = "arrow,ltc2422", },{}};MODULE_DEVICE_TABLE(of, ltc2422_dt_ids);static const struct spi_device_id ltc2422_id[] = {{.name = "ltc2422", },{}};MODULE_DEVICE_TABLE(spi, ltc2422_id);static struct spi_driver ltc2422_driver = {.driver = {.name= "ltc2422",.owner= THIS_MODULE,.of_match_table = ltc2422_dt_ids,},.probe= ltc2422_probe,.remove= ltc2422_remove,.id_table= ltc2422_id,};module_spi_driver(ltc2422_driver);MODULE_AUTHOR(" ");MODULE_DESCRIPTION("LTC2422 DUAL ADC with triggering");MODULE_LICENSE("GPL");

18.5 应用代码

#include <stdio.h>#include <stdint.h>#include <stdlib.h>#include <string.h>#include <unistd.h>#include <fcntl.h>#include <sys/ioctl.h>#include <linux/types.h>int8_t read_adc();/* The LTC2422 least significant bit value with 5V full-scale */float LTC2422_lsb = 4.7683761E-6; /* The LTC2422 least significant bit value with 3.3V full-scale *//* float LTC2422_lsb = 3.1471252E-6; *//* check which number is the ADC iio:deviceX and replace x by the number */#define LTC2422_FILE_VOLTAGE"/sys/bus/iio/devices/iio:device2/out_voltage0_raw"#define SPI_DATA_CHANNEL_OFFSET 22#define SPI_DATA_CHANNEL_MASK (1 << SPI_DATA_CHANNEL_OFFSET)#define LTC2422_CONVERSION_TIME137 /* ms *//* * Returns the Data and Channel Number(0- channel 0, 1-Channel 1)* Returns the status of the SPI read. 0=successful, 1=unsuccessful.*/int8_t LTC2422_read(uint8_t *adc_channel, int32_t *code);/* Returns the Calculated Voltage from the ADC Code */float LTC2422_voltage(uint32_t adc_code, float LTC2422_lsb);int8_t LTC2422_read(uint8_t *adc_channel, int32_t *code){int a2dReading = 0;FILE *f = fopen(LTC2422_FILE_VOLTAGE, "r");int read = fscanf(f, "%d", &a2dReading);if (read <= 0) {printf("ERROR: Unable to read values from voltage input file.\n");exit(-1);}/* Determine the channel number */*adc_channel = (a2dReading & SPI_DATA_CHANNEL_MASK) ? 1 : 0;*code = a2dReading;fclose(f);return(0);}/* Returns the Calculated Voltage from the ADC Code */float LTC2422_voltage(uint32_t adc_code, float LTC2422_lsb){float adc_voltage;if (adc_code & 0x200000){adc_code &= 0xFFFFF; /* Clears Bits 20-23 */adc_voltage=((float)adc_code)*LTC2422_lsb;}else{adc_code &= 0xFFFFF; /* Clears Bits 20-23 */adc_voltage = -1*((float)adc_code)*LTC2422_lsb;}return(adc_voltage);}void delay(unsigned int ms){usleep(ms*1000);}int8_t read_adc(){float adc_voltage;int32_t adc_code;uint8_t adc_channel;int32_t adc_code_array; int8_t return_code;int a2dReading = 0;LTC2422_read(&adc_channel, &adc_code);delay(LTC2422_CONVERSION_TIME);LTC2422_read(&adc_channel, &adc_code);adc_voltage = LTC2422_voltage(adc_code, LTC2422_lsb);printf("the value of ADC channel %d\n", adc_channel);printf("is : %6.4f\n", adc_voltage);delay(LTC2422_CONVERSION_TIME);LTC2422_read(&adc_channel, &adc_code);adc_voltage = LTC2422_voltage(adc_code, LTC2422_lsb);printf("the value of ADC channel %d\n", adc_channel);printf("is : %6.4f\n", adc_voltage);return(0);}int main(void){read_adc();printf("Application termined\n");return 0;}