RK 利用SARADC 来做多个按键

#DTS配置
- #配置DTS节点
- #驱动文件中匹配 DTS 节点
#驱动说明
- #获取ADC通道
- #获取ADC值
- #计算采集到的电压
- #接口说明
#调试方法
- #节点ADC值

RK3399开发板上的 AD 接口有两种，分别为：温度传感器 (Temperature Sensor)、逐次逼近ADC (Successive Approximation Register)。

TS-ADC(Temperature Sensor)：支持两通道，时钟频率必须低于800KHZ
AR-ADC(Successive Approximation Register)：支持六通道单端10位的SAR-ADC，时钟频率必须小于13MHZ。内核采用工业 I/O 子系统来控制 ADC，该子系统主要为 AD 转换或者 DA 转换的传感器设计。下面以SAR-ADC为例子，介绍 ADC 的基本配置方法。

#DTS配置

#配置DTS节点

SAR-ADC 的 DTS 节点在 kernel/arch/arm64/boot/dts/rockchip/rk3399.dtsi 文件中定义，如下所示：

saradc: saradc@ff100000 {compatible = "rockchip,rk3399-saradc";reg = <0x0 0xff100000 0x0 0x100>;interrupts = <GIC_SPI 62 IRQ_TYPE_LEVEL_HIGH 0>;#io-channel-cells = <1>;clocks = <&cru SCLK_SARADC>, <&cru PCLK_SARADC>;clock-names = "saradc", "apb_pclk";resets = <&cru SRST_P_SARADC>;reset-names = "saradc-apb";status = "disabled";};

用户首先需在DTS文件中添加ADC的资源描述：

&rk_key {compatible = "rockchip,key";status = "okay";io-channels = <&saradc 1>;vol-up-key {linux,code = <114>;label = "volume up";rockchip,adc_value = <1>;};vol-down-key {linux,code = <115>;label = "volume down";rockchip,adc_value = <170>;};power-key {gpios = <&gpio0 5 GPIO_ACTIVE_LOW>;linux,code = <116>;label = "power";gpio-key,wakeup;};menu-key {linux,code = <59>;label = "menu";rockchip,adc_value = <746>;};home-key {linux,code = <102>;label = "home";rockchip,adc_value = <355>;};back-key {linux,code = <158>;label = "back";rockchip,adc_value = <560>;};camera-key {linux,code = <212>;label = "camera";rockchip,adc_value = <450>;};
};

这里申请的是SARADC通道1

#驱动文件中匹配 DTS 节点

驱动key:drivers/input/keyboard/rk_keys.c 首先在驱动文件中定义 of_device_id 结构体数组：

static const struct of_device_id rk_key_match[] = {{ .compatible = "rockchip,key", .data = NULL},{},
};

然后将该结构体数组填充到 platform_driver 中：

static struct platform_driver keys_device_driver = {.probe      = keys_probe,.remove     = keys_remove,.driver     = {.name   = "rk-keypad",.owner  = THIS_MODULE,.of_match_table = rk_key_match,
#ifdef CONFIG_PM.pm = &keys_pm_ops,
#endif}
};

接着在keys_probe中使用work 进行polling ：

    /* adc polling work */if (ddata->chan) {INIT_DELAYED_WORK(&ddata->adc_poll_work, adc_key_poll);schedule_delayed_work(&ddata->adc_poll_work,┊   ┊ ADC_SAMPLE_JIFFIES);}

ADC key Poll DTS资源解析

static void adc_key_poll(struct work_struct *work)
{struct rk_keys_drvdata *ddata;int i, result = -1;ddata = container_of(work, struct rk_keys_drvdata, adc_poll_work.work);if (!ddata->in_suspend) {result = rk_key_adc_iio_read(ddata);/**读取SARADC值*/if (result > INVALID_ADVALUE &&┊   result < (EMPTY_DEFAULT_ADVALUE - ddata->drift_advalue))ddata->result = result;for (i = 0; i < ddata->nbuttons; i++) {struct rk_keys_button *button = &ddata->button[i];if (!button->adc_value)continue;if (result < button->adc_value + ddata->drift_advalue &&┊   result > button->adc_value - ddata->drift_advalue)button->adc_state = 1;else                 button->adc_state = 0;if (button->state != button->adc_state)mod_timer(&button->timer,┊ jiffies + DEBOUNCE_JIFFIES);}}schedule_delayed_work(&ddata->adc_poll_work, ADC_SAMPLE_JIFFIES);
}

#驱动说明

#获取ADC通道

在解析资源DTS时获取对应的通道 struct iio_channel *chan; /定义 IIO 通道结构体chan = iio_channel_get(&pdev->dev, NULL); /获取 IIO 通道结构体/

static int rk_keys_parse_dt(struct rk_keys_drvdata *pdata,struct platform_device *pdev)
{struct device_node *node = pdev->dev.of_node;struct device_node *child_node;struct iio_channel *chan;int ret, gpio, i = 0;u32 code, adc_value, flags, drift;if (of_property_read_u32(node, "adc-drift", &drift))pdata->drift_advalue = DRIFT_DEFAULT_ADVALUE;else    pdata->drift_advalue = (int)drift;chan = iio_channel_get(&pdev->dev, NULL);
...............

#获取ADC值

在adc_key polling中调用 iio_read_channel_raw 函数读取 AD 采集的原始数据并存入 val 中

  ret = iio_read_channel_raw(channel, &val);

#计算采集到的电压

Vref / (2^n-1) = Vresult / raw

注：

Vref 为标准电压 n 为 AD 转换的位数 Vresult 为用户所需要的采集电压 raw 为 AD 采集的原始数据

#接口说明

struct iio_channel *iio_channel_get(struct device *dev, const char *consumer_channel);

功能：获取 iio 通道描述
参数：
- dev: 使用该通道的设备描述指针
- consumer_channel: 该设备所使用的 IIO 通道描述指针

void iio_channel_release(struct iio_channel *chan);

功能：释放 iio_channel_get 函数获取到的通道
参数：
- chan：要被释放的通道描述指针

int iio_read_channel_raw(struct iio_channel *chan, int *val);

功能：读取 chan 通道 AD 采集的原始数据。
参数：
- chan：要读取的采集通道指针
- val：存放读取结果的指针

#调试方法

#节点ADC值

cat /sys/bus/iio/devices/iio\:device1/in_voltage*_raw
876
1021
164
512
513
349

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