VS-RK3XXX開發(fā)板上的 AD 接口分為：高速 ADC 流接口 (High-speed ADC Stream Interface)、溫度傳感器 (Temperature Sensor)、逐次逼近ADC (Successive Approximation Register)。本文主要介紹 ADC 的基本配置方法。
內(nèi)核采用工業(yè) I/O 子系統(tǒng)來控制 ADC，該子系統(tǒng)主要為 AD 轉(zhuǎn)換或者 DA 轉(zhuǎn)換的傳感器設(shè)計。
其相關(guān)數(shù)據(jù)結(jié)構(gòu)以及配置方法如下：
iio_channel 結(jié)構(gòu)體
struct iio_channel {
struct iio_dev *indio_dev;//工業(yè) I/O設(shè)備
const struct iio_chan_spec *channel;//I/O通道
void *data;
};
iio_dev 結(jié)構(gòu)體
該結(jié)構(gòu)體主要用于描述 IO 口所屬的設(shè)備，其具體定義如下：
該結(jié)構(gòu)體主要用于描述 IO 口所屬的設(shè)備，其具體定義如下：
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[IIO_MAX_GROUPS + 1];
int groupcounter;
unsigned long flags;
#if defined(CONFIG_DEBUG_FS)
struct dentry *debugfs_dentry;
unsigned cached_reg_addr;
#endif
};
2.3 iio_chan_spec結(jié)構(gòu)體
該結(jié)構(gòu)體主要用于描述單個通道的屬性，具體定義如下：
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[IIO_MAX_GROUPS + 1];
int groupcounter;
unsigned long flags;
#if defined(CONFIG_DEBUG_FS)
struct dentry *debugfs_dentry;
unsigned cached_reg_addr;
#endif
};
2.3 iio_chan_spec結(jié)構(gòu)體
該結(jié)構(gòu)體主要用于描述單個通道的屬性，具體定義如下：
struct iio_chan_spec {
enum iio_chan_type type; //描述通道類型
int channel; //通道號
int channel2; //通道號
unsigned long address; //通道地址
int scan_index;
struct {
char sign;
u8 realbits;
u8 storagebits;
u8 shift;
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 配置步驟
enum iio_chan_type type; //描述通道類型
int channel; //通道號
int channel2; //通道號
unsigned long address; //通道地址
int scan_index;
struct {
char sign;
u8 realbits;
u8 storagebits;
u8 shift;
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 配置步驟
iio_chan_spec結(jié)構(gòu)體
該結(jié)構(gòu)體主要用于描述單個通道的屬性，具體定義如下：
該結(jié)構(gòu)體主要用于描述單個通道的屬性，具體定義如下：
struct iio_chan_spec {
enum iio_chan_type type; //描述通道類型
int channel; //通道號
int channel2; //通道號
unsigned long address; //通道地址
int scan_index;
struct {
char sign;
u8 realbits;
u8 storagebits;
u8 shift;
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;
};
enum iio_chan_type type; //描述通道類型
int channel; //通道號
int channel2; //通道號
unsigned long address; //通道地址
int scan_index;
struct {
char sign;
u8 realbits;
u8 storagebits;
u8 shift;
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;
};
配置步驟
3.1 配置DTS節(jié)點
ADC的 DTS 節(jié)點在 kernel/arch/arm/boot/dts/rk3288.dtsi 文件中定義，如下所示：
3.1 配置DTS節(jié)點
ADC的 DTS 節(jié)點在 kernel/arch/arm/boot/dts/rk3288.dtsi 文件中定義，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";
};
用戶只需在rk3288.dts 文件中添加通道定義，并將其 status 改為 "okay" 即可：
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";
};
用戶只需在rk3288.dts 文件中添加通道定義，并將其 status 改為 "okay" 即可：
&adc {
status = "okay";
adc_test{
compatible = "rockchip,adc_test";
io-channels = <&adc 0>;
};
};
3.2 在驅(qū)動文件中匹配 DTS 節(jié)點
在驅(qū)動文件中定義 of_device_id 結(jié)構(gòu)體數(shù)組：
status = "okay";
adc_test{
compatible = "rockchip,adc_test";
io-channels = <&adc 0>;
};
};
3.2 在驅(qū)動文件中匹配 DTS 節(jié)點
在驅(qū)動文件中定義 of_device_id 結(jié)構(gòu)體數(shù)組：
static const struct of_device_id of_XXX_match[] = {
{ .compatible = "rockchip,adc_test" },
{ /* Sentinel */ }
};
將該結(jié)構(gòu)體數(shù)組填充到要使用 ADC 的 platform_driver 中。
{ .compatible = "rockchip,adc_test" },
{ /* Sentinel */ }
};
將該結(jié)構(gòu)體數(shù)組填充到要使用 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 獲取 AD 通道
struct iio_channel *chan; //定義 IIO 通道結(jié)構(gòu)體
chan = iio_channel_get(&pdev->dev, NULL); //獲取 IIO 通道結(jié)構(gòu)體
注：iio_channel_get 通過 probe 函數(shù)傳進(jìn)來的參數(shù) pdev 獲取 IIO 通道結(jié)構(gòu)體，probe 函數(shù)如下：
.probe = ...,.remove = ...,.driver = {
.name = "..",.owner = THIS_MODULE,#ifdef CONFIG_OF.of_match_table = of_XXX_match,#endif},
};
3.3 獲取 AD 通道
struct iio_channel *chan; //定義 IIO 通道結(jié)構(gòu)體
chan = iio_channel_get(&pdev->dev, NULL); //獲取 IIO 通道結(jié)構(gòu)體
注：iio_channel_get 通過 probe 函數(shù)傳進(jìn)來的參數(shù) pdev 獲取 IIO 通道結(jié)構(gòu)體，probe 函數(shù)如下：
static int XXX_probe(struct platform_device *pdev);
3.4 讀取 AD 采集到的原始數(shù)據(jù)
int val,ret;
ret = iio_read_channel_raw(chan, &val);
調(diào)用 iio_read_channel_raw 函數(shù)讀取 AD 采集的原始數(shù)據(jù)并存入 val 中。
3.4 讀取 AD 采集到的原始數(shù)據(jù)
int val,ret;
ret = iio_read_channel_raw(chan, &val);
調(diào)用 iio_read_channel_raw 函數(shù)讀取 AD 采集的原始數(shù)據(jù)并存入 val 中。
3.5 計算采集到的電壓
使用標(biāo)準(zhǔn)電壓將 AD 轉(zhuǎn)換的值轉(zhuǎn)換為用戶所需要的電壓值。其計算公式如下：
使用標(biāo)準(zhǔn)電壓將 AD 轉(zhuǎn)換的值轉(zhuǎn)換為用戶所需要的電壓值。其計算公式如下：
Vref / (2^n-1) = Vresult / raw
注：
注：
Vref 為標(biāo)準(zhǔn)電壓
n 為 AD 轉(zhuǎn)換的位數(shù)
Vresult 為用戶所需要的采集電壓
raw 為 AD 采集的原始數(shù)據(jù)
例如，標(biāo)準(zhǔn)電壓為 1.8V，AD 采集位數(shù)為 10 位，AD 采集到的原始數(shù)據(jù)為 568，則：
Vresult = (1800mv * 56
/ 1023;
4 ADC 常用函數(shù)接口
struct iio_channel *iio_channel_get(struct device *dev, const char *consumer_channel);
功能：獲取 iio 通道描述
/ 1023;4 ADC 常用函數(shù)接口
struct iio_channel *iio_channel_get(struct device *dev, const char *consumer_channel);
功能：獲取 iio 通道描述
參數(shù)：
dev: 使用該通道的設(shè)備描述指針
consumer_channel: 該設(shè)備所使用的 IIO 通道描述指針
void iio_channel_release(struct iio_channel *chan);
功能：釋放 iio_channel_get 函數(shù)獲取到的通道
功能：釋放 iio_channel_get 函數(shù)獲取到的通道
參數(shù)：
chan：要被釋放的通道描述指針
int iio_read_channel_raw(struct iio_channel *chan, int *val);
功能：讀取 chan 通道 AD 采集的原始數(shù)據(jù)。
功能：讀取 chan 通道 AD 采集的原始數(shù)據(jù)。
參數(shù)：
chan：要讀取的采集通道指針
val：存放讀取結(jié)果的指針