Asynchronous acquisition API
[Level 2 API]

Collaboration diagram for Asynchronous acquisition API:

Functions
int	a4l_async_read (a4l_desc_t *dsc, void *buf, size_t nbyte, unsigned long ms_timeout)
	Perform asynchronous read operation on the analog input subdevice.
int	a4l_async_write (a4l_desc_t *dsc, void *buf, size_t nbyte, unsigned long ms_timeout)
	Perform asynchronous write operation on the analog input subdevice.

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Function Documentation

int a4l_async_read	(	a4l_desc_t *	dsc,
		void *	buf,
		size_t	nbyte,
		unsigned long	ms_timeout
	)

Perform asynchronous read operation on the analog input subdevice.

The function a4l_async_read() is only useful for acquisition configured through an Analogy command.

Parameters:

[in]	dsc	Device descriptor filled by a4l_open() (and optionally a4l_fill_desc())
[out]	buf	Input buffer
[in]	nbyte	Number of bytes to read
[in]	ms_timeout	The number of miliseconds to wait for some data to be available. Passing A4L_INFINITE causes the caller to block indefinitely until some data is available. Passing A4L_NONBLOCK causes the function to return immediately without waiting for any available data

Returns:

Number of bytes read, otherwise negative error code:

• -EINVAL is returned if some argument is missing or wrong, the descriptor should be checked; check also the kernel log
• -ENOENT is returned if the device's reading subdevice is idle (no command was sent)
• -EFAULT is returned if a user <-> kernel transfer went wrong
• -EINTR is returned if calling task has been unblocked by a signal

References a4l_poll(), a4l_sys_read(), a4l_descriptor::fd, and a4l_descriptor::idx_read_subd.

int a4l_async_write	(	a4l_desc_t *	dsc,
		void *	buf,
		size_t	nbyte,
		unsigned long	ms_timeout
	)

Perform asynchronous write operation on the analog input subdevice.

The function a4l_async_write() is only useful for acquisition configured through an Analogy command.

Parameters:

[in]	dsc	Device descriptor filled by a4l_open() (and optionally a4l_fill_desc())
[in]	buf	Ouput buffer
[in]	nbyte	Number of bytes to write
[in]	ms_timeout	The number of miliseconds to wait for some free area to be available. Passing A4L_INFINITE causes the caller to block indefinitely until some data is available. Passing A4L_NONBLOCK causes the function to return immediately without waiting any available space to write data.

Returns:

Number of bytes written, otherwise negative error code:

• -EINVAL is returned if some argument is missing or wrong, the descriptor should be checked; check also the kernel log
• -ENOENT is returned if the device's reading subdevice is idle (no command was sent)
• -EFAULT is returned if a user <-> kernel transfer went wrong
• -EINTR is returned if calling task has been unblocked by a signal

References a4l_poll(), a4l_sys_write(), a4l_descriptor::fd, and a4l_descriptor::idx_write_subd.