VS-RK3XXX Android7.1系统调试ADC驱动配置
VS-RK3XXX开发板上的 AD 接口分为：高速 ADC 流接口 (High-speed ADC Stream Interface)、温度传感器 (Temperature Sensor)、逐次逼近ADC (Successive Approximation Register)。本文主要介绍 ADC 的基本配置方法。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。其相关数据结构以及配置方法如下：iio_channel 结构体
struct iio_channel {
struct iio_dev *indio_dev;//工业 I/O设备
const struct iio_chan_spec *channel;//I/O通道
void *data;
};iio_dev 结构体
该结构体主要用于描述 IO 口所属的设备，其具体定义如下：struct iio_dev {
int id;
int modes;
int currentmode;
struct device dev;
struct iio_event_interface*event_interface;
struct iio_buffer *buffer;
struct list_head buffer_list;
int scan_bytes;
struct mutex mlock;
const unsigned long *available_scan_masks;
unsigned masklength;
const unsigned long *active_scan_mask;
bool scan_timestamp;
unsigned scan_index_timestamp;
struct iio_trigger *trig;
struct iio_poll_func *pollfunc;
struct iio_chan_spec const*channels;
int num_channels;
struct list_head channel_attr_list;
struct attribute_group chan_attr_group;
const char *name;
const struct iio_info *info;
struct mutex info_exist_lock;
const struct iio_buffer_setup_ops *setup_ops;
struct cdev chrdev;
#define IIO_MAX_GROUPS 6
const struct attribute_group *groups;
int groupcounter;
unsigned long flags;
#if defined(CONFIG_DEBUG_FS)
struct dentry *debugfs_dentry;
unsigned cached_reg_addr;
#endif
};
2.3 iio_chan_spec结构体
该结构体主要用于描述单个通道的属性，具体定义如下：struct iio_chan_spec {
enum iio_chan_typetype; //描述通道类型
int channel; //通道号
int channel2; //通道号
unsigned long address; //通道地址
int scan_index;
struct {
char sign;
u8realbits;
u8storagebits;
u8shift;
enum iio_endian endianness;
} scan_type;
long info_mask;
long info_mask_separate;
long info_mask_shared_by_type;
long event_mask;
const struct iio_chan_spec_ext_info *ext_info;
const char *extend_name;
const char *datasheet_name;
unsigned modified:1;
unsigned indexed:1;
unsigned output:1;
unsigned differential:1;
};
3 配置步骤iio_chan_spec结构体
该结构体主要用于描述单个通道的属性，具体定义如下：struct iio_chan_spec {
enum iio_chan_typetype; //描述通道类型
int channel; //通道号
int channel2; //通道号
unsigned long address; //通道地址
int scan_index;
struct {
char sign;
u8realbits;
u8storagebits;
u8shift;
enum iio_endian endianness;
} scan_type;
long info_mask;
long info_mask_separate;
long info_mask_shared_by_type;
long event_mask;
const struct iio_chan_spec_ext_info *ext_info;
const char *extend_name;
const char *datasheet_name;
unsigned modified:1;
unsigned indexed:1;
unsigned output:1;
unsigned differential:1;
};配置步骤
3.1 配置DTS节点
ADC的 DTS 节点在 kernel/arch/arm/boot/dts/rk3288.dtsi 文件中定义，如下所示：adc: adc@ff100000 {
compatible = "rockchip,saradc";
reg = <0xff100000 0x100>;
interrupts = <GIC_SPI 36 IRQ_TYPE_LEVEL_HIGH>;
#io-channel-cells = <1>;
io-channel-ranges;rockchip,adc-vref = <1800>;
clock-frequency = <1000000>;
clocks = <&clk_saradc>, <&clk_gates7 1>;
clock-names = "saradc", "pclk_saradc";
status = "disabled";
};
用户只需在rk3288.dts 文件中添加通道定义，并将其 status 改为 "okay" 即可：&adc {
status = "okay";
adc_test{
compatible = "rockchip,adc_test";
io-channels = <&adc 0>;
};
};
3.2 在驱动文件中匹配 DTS 节点
在驱动文件中定义 of_device_id 结构体数组：static const struct of_device_id of_XXX_match[] = {
{ .compatible = "rockchip,adc_test" },
{ /* Sentinel */ }
};
将该结构体数组填充到要使用 ADC 的 platform_driver 中。static struct platform_driver XXX_driver = {
.probe = ...,.remove = ...,.driver = {
.name = "..",.owner= THIS_MODULE,#ifdef CONFIG_OF.of_match_table = of_XXX_match,#endif},
};
3.3 获取 AD 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
注：iio_channel_get 通过 probe 函数传进来的参数 pdev 获取 IIO 通道结构体，probe 函数如下：static int XXX_probe(struct platform_device *pdev);
3.4 读取 AD 采集到的原始数据
int val,ret;
ret = iio_read_channel_raw(chan, &val);
调用 iio_read_channel_raw 函数读取 AD 采集的原始数据并存入 val 中。3.5 计算采集到的电压
使用标准电压将 AD 转换的值转换为用户所需要的电压值。其计算公式如下：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 采集的原始数据例如，标准电压为 1.8V，AD 采集位数为 10 位，AD 采集到的原始数据为 568，则：Vresult = (1800mv * 568) / 1023;
4 ADC 常用函数接口
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
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