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Linux IIO库操作

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libiio 提供了统一的接口来操作位于iio子系统下的设备。

结构

由上图可以看出: - libiio 具有 local backend 和 network backend 两种后端 + local backend 用于与本地的 sysfs 中的文件交互 + network backend 通过 iiod 服务器运作，可以通过网络连接将测试数据发送到其他平台上

编译

  • 在github 下载最新稳定版代码
  • 编写工具链配置文件 toolchain.cmake
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mkdir build
cd build
# 指定编译器设定文件以及取消掉不必要的编译选项
# 第一次cmake生成基础文件
cmake -DCMAKE_TOOLCHAIN_FILE=../toolchain.cmake ../
# 第二次才是重新配置选项
cmake-gui -DCMAKE_TOOLCHAIN_FILE=../toolchain.cmake ../

make all
make install DESTDIR=/home/cec/iio

API

参考官方手册 做简单整理。

API由以下4部分组成:

  • iio_channel : 代表一个设备上的一个通道
  • iio_device : 代表一个具体的设备实例，一个 iio_device 可能会包含多个 iio_channel
  • iio_buffer : 针对设备的缓存，一个 iio_device 对应一个 iio_buffer
  • iio_context : 可能包含多个 iio_device

iio 设备在sysfs中可以读写的文件名为: <in/out>_<channel>_<attr> 。

context

创建与消除

一般一个进程创建一个 iio_context 对象，以代表对 IIO 设备的打包使用： - 在创建 context 就会遍历 iio:device 以集合设备

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/**
 ,* @brief Create a context from local IIO devices (Linux only)
 ,* @Returns
 ,* On success, A pointer to an iio_context structure
 ,* On failure, NULL is returned and errno is set appropriately
 ,*/
__api struct iio_context* iio_create_local_context 	(void);
/**
 ,* @brief Create a context from the network.
 ,* @param host:	Hostname, IPv4 or IPv6 address where the IIO Daemon is running 
 ,* @Returns
 ,* On success, a pointer to an iio_context structure
 ,* On failure, NULL is returned and errno is set appropriately
 ,*/
__api struct iio_context* iio_create_network_context 	(const char *  host);
/**
 ,* @brief Destroy the given context. 
 ,*/
__api void iio_context_destroy 	(struct iio_context * ctx);

与设备的关系

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/**
 ,* @brief Enumerate the devices found in the given context.
 ,* @ret : The number of devices found 
 ,*/
unsigned int iio_context_get_devices_count 	(const struct iio_context * ctx);
/**
 ,* @brief Get the device present at the given index.
 ,*/
struct iio_device* iio_context_get_device 	(const struct iio_context *  	ctx,
                                                unsigned int  	index);
/**
 ,* @brief :Retrieve the device ID (e.g. iio:device0) 
 ,*/
const char* iio_device_get_id 	(const struct iio_device *  	dev);
/**
 ,* @brief : Retrieve the device name (e.g. xadc) 
 ,*/
const char* iio_device_get_name 	(const struct iio_device *  	dev);
/**
 ,* @brief : Try to find a device structure by its name of ID.
 ,*/
struct iio_device* iio_context_find_device 	(const struct iio_context *  	ctx,
                                                const char *  	name);

channels

注意: 两个channels可以具有相同的ID，分别代表输入和输出！

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/**
 ,* @brief : Enumerate the channels of the given device. 
 ,*/
unsigned int iio_device_get_channels_count 	(const struct iio_device *  	dev);
/**
 ,* @brief : Get the channel present at the given index. 
 ,*/
struct iio_channel* iio_device_get_channel 	(const struct iio_device *  	dev,
                                                unsigned int  	index);
/**
 ,* @brief : Try to find a channel structure by its name of ID.
 ,* @param output:	True if the searched channel is output, False otherwise 
 ,*/
struct iio_channel* iio_device_find_channel 	( 	const struct iio_device *  	dev,
                                                  const char *  	name,
                                                  bool  	output
                                                  );
/**
 ,* @brief : Return True if the given channel is an output channel. 
 ,*/
bool iio_channel_is_output 	(const struct iio_channel *  	chn);
/**
 ,* @brief : Retrieve the channel ID (e.g. voltage0) 
 ,*/
const char* iio_channel_get_id 	(const struct iio_channel * chn);
/**
 ,* @brief : Retrieve the channel name (e.g. vccint) 
 ,*/
const char* iio_channel_get_name 	(const struct iio_channel *  chn);

属性

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/**
 ,* @brief : Enumerate the device-specific attributes of the given device. 
 ,*/
unsigned int iio_device_get_attrs_count(const struct iio_device *  	dev);
/**
 ,* @brief : Get the device-specific attribute present at the given index. 
 ,*/
const char* iio_device_get_attr 	( 	const struct iio_device *  	dev,
                                      unsigned int  	index);
unsigned int iio_channel_get_attrs_count 	( 	const struct iio_channel *  chn);
const char* iio_channel_get_attr 	( 	const struct iio_channel *  	chn,
                                      unsigned int  	index 
                                      );
/**
 ,* @brief : Try to find a device-specific attribute by its name. 
 ,* @NOTE: This function is useful to detect the presence of an attribute. It can also be used to retrieve the name of an attribute a * s a pointer to a static string from a dynamically allocated string. 
 ,*/
const char* iio_device_find_attr 	( 	const struct iio_device *  	dev,
                                      const char *  	name 
                                      );
const char* iio_channel_find_attr 	( 	const struct iio_channel *  	chn,
                                        const char *  	name 
                                        );

参数的读写

  • 读取设备参数
    • iio_device_attr_read()
    • iio_device_attr_read_all()
    • iio_device_attr_read_bool()
    • iio_device_attr_read_longlong()
    • iio_device_attr_read_double()
  • 读取通道参数
    • iio_channel_attr_read()
    • iio_channel_attr_read_all()
    • iio_channel_attr_read_bool()
    • iio_channel_attr_read_longlong()
    • iio_channel_attr_read_double()
  • 读取调试参数:并不是每个设备都有debugfs
    • iio_device_debug_attr_read()
    • iio_device_debug_attr_read_all()
    • iio_device_debug_attr_read_bool()
    • iio_device_debug_attr_read_longlong()
    • iio_device_debug_attr_read_double()
    • iio_device_get_debug_attrs_count() : 获取debug参数数目
    • iio_device_get_debug_attr(): 得到attr
    • iio_device_find_debug_attr(): 寻找attr
  • 写设备参数
    • iio_device_attr_write()
    • iio_device_attr_write_all()
    • iio_device_attr_write_bool()
    • iio_device_attr_write_longlong()
    • iio_device_attr_write_double()
  • 写通道参数
    • iio_channel_attr_write()
    • iio_channel_attr_write_all()
    • iio_channel_attr_write_bool()
    • iio_channel_attr_write_longlong()
    • iio_channel_attr_write_double()
  • 写调试参数:并不是每个设备都有debugfs
    • iio_device_debug_attr_write()
    • iio_device_debug_attr_write_all()
    • iio_device_debug_attr_write_bool()
    • iio_device_debug_attr_write_longlong()
    • iio_device_debug_attr_write_double()
  • 寄存器的直接读写:并不是每个设备都有
    • iio_device_reg_read()
    • iio_device_reg_write()

触发

  • iio_device_is_trigger() : 检查设备是否可以使用触发
  • iio_device_get_trigger(): 是否已经绑定触发
  • iio_device_set_trigger(): 绑定触发或解绑

获取采样的值

在 libiio 中使用 iio_buffer 来获取或设置设备的值。

  • 在使用buffer之前需要先使能或关闭对应的采样通道:
    • iio_channel_enable() / iio_channel_disable()
    • iio_channel_is_scan_element() : 检查此通道是否可用于buffer
  • 然后再创建buffer
    • iio_device_create_buffer()
    • iio_buffer_destroy() : 不使用时关闭
  • 当为输入通道时，还需要刷新依次缓存
    • iio_buffer_refill()

缓存的操作

  • 向缓存写数据:
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size_t iio_buf_size = iio_buffer_end(buffer) - iio_buffer_start(buffer);
size_t count = MAX(sizeof(samples_buffer), iio_buf_size);
memcpy(iio_buffer_start(buffer), samples_buffer, count);
/**
 ,* @note : 当申请的缓存时环形队列时并且kernel中支持环形队列,缓存的值会自动更新到kernel
 ,* 否则上层需要使用 iio_buffer_push() 来主动发送缓存到kernel
 ,*/
  • 回调: 当缓存读入数据或缓存发送时需要填入数据，都会触发回调
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ssize_t sample_cb(const struct iio_channel *chn, void *src, size_t bytes, void *d)
{
  /* Use "src" to read or write a sample for this channel */
}
int main(void)
{
  ...
  iio_buffer_foreach_sample(buffer, sample_cb, NULL);
  ...
}
  • 循环的读写
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for (void *ptr = iio_buffer_first(buffer, channel);
     ptr < iio_buffer_end(buffer);
     ptr += iio_buffer_step(buffer)) {
  /* Use "ptr" to read or write a sample for this channel */
 }

获取版本号

使用 iio_library_get_version() 来获取版本号进行区分，以使用对应的功能。

实例

基本思路如下: - 创建一个context - 找寻设备 - 获取通道 - 进行读写

以气压计 ms5611 为例:

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struct iio_context * context;
struct iio_device  * baro;
struct iio_channel * mb_temp;

context = iio_create_local_context();
assert(context != NULL);

baro = iio_context_find_device(context, "ms5611");
if(baro == NULL)
  {
    printf("can not find ms5611!\n");
  }
printf("ms5611 has %d channels\n", iio_device_get_channels_count(baro));
mb_temp = iio_device_find_channel(baro,
                                         "temp", false);

double f_temp_val = 0;
if(iio_channel_attr_read_double(mb_temp, "input", &f_temp_val))
  {
    printf("read error!\n");
  }
else
  {
    printf("value is = %f\n", f_temp_val);
  }