RK 利用SARADC 来做多个按键

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