hil_read_digital_buffer :: Quanser C Functions

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hil_read_digital_buffer

Reads the specified number of samples from the digital channels at the indicated sampling rate.

Description

The hil_read_digital_buffer function reads the specified number of samples from the digital input channels at the given sampling rate. The function does not return until the data has been read.

Warning Many cards allow the digital I/O lines to be programmed as inputs or outputs. The digital I/O lines are configured as inputs or outputs using the hil_set_digital_directions function. All the channels which will be used as digital inputs must be configured as inputs using this function. Failure to configure the digital I/O may result in the hil_read_digital_buffer function failing to read those inputs.

Prototype

t_error 
hil_read_digital_buffer(t_card card, t_clock clock, t_double frequency, t_uint32 num_samples,
                        const t_uint32 digital_channels[], t_uint32 num_channels, t_boolean buffer[]);

Parameters

t_card card

A handle to the board, as returned by hil_open

t_clock clock

The clock used to time the operation. Note that some clocks allow faster sampling rates than others. See Clocks for more information on clocks.

Select a board type from the list for board-specific details: .

t_double frequency

The frequency in Hertz at which to sample the digital input channels. For example, if frequency is set to 1000, then the hil_read_digital_buffer function will read all the selected channels every millisecond.

t_uint32 num_samples

The number of samples to collect. Each "sample" consists of all the digital input channels specified. For example, if frequency is set to 1000 and num_samples is set to 5000, then the hil_read_digital_buffer function will return after 5 seconds with 5000 samples. If 3 channels have been selected, then the output buffer will contain 15,000 elements.

const t_uint32 [] digital_channels

An array containing the channel numbers of the digital inputs to be read.

Select a board type from the list for board-specific details: .

t_uint32 num_channels

The number of channels specified in the digital_channels array.

t_boolean [] buffer

An array for receiving the values read from the digital inputs. The array must contain num_channels * num_samples elements. The array is organized as a linear array of samples, with each sample consisting of a group of channels. For example, if digital input channels 0, 1 and 3 are being read, than the data appears in the array as follows, where the numbers correspond to channel numbers:

...

This ordering is equivalent to defining the buffer as:

t_boolean buffer[num_samples][num_channels];

If the buffer is defined this way then pass the buffer as the buffer argument using the syntax: &buffer[0][0].

Return value

The return value is the number of samples successfully read. Otherwise a negative error code is returned. Error codes are defined in quanser_errors.h. A suitable error message may be retrieved using msg_get_error_message.

Error codes

QERR_HIL_READ_DIGITAL_BUFFER_NOT_SUPPORTED

This function is not supported by the board-specific HIL driver for this board type.

QERR_INVALID_CARD_HANDLE

An invalid card handle was passed as an argument. Once a card has been closed using hil_close the card handle is invalid.

QERR_TOO_MANY_DIGITAL_INPUT_CHANNELS

Too many digital input channels were specified.

QERR_INVALID_DIGITAL_INPUT_CHANNEL

One of the digital input channels that was specified is not a valid channel number. Channel numbers range from 0 to one less than the number of channels.

QERR_DRIVER_INCOMPATIBLE_WITH_BOARD_DLL

The board-specific HIL driver passed an invalid parameter to the operating system specific kernel-level driver for the board. The board-specific HIL driver is likely not compatible with the operating system specific kernel-level driver for the board. Make sure both are up-to-date and compatible versions.

QERR_INTERNAL_BUFFER_TOO_SMALL

The board-specific HIL driver used an internal buffer that was too small for the operating system specific kernel-level driver for the board. The board-specific HIL driver is likely not compatible with the operating system specific kernel-level driver for the board. Make sure both are up-to-date and compatible versions.

QERR_OUT_OF_REQUIRED_SYSTEM_RESOURCES

There are not enough system resources to perform the requested operation. Try rebooting, requesting fewer samples, or adding more memory to your machine.

QERR_OUT_OF_MEMORY

There is not enough memory to perform the operation.

Requirements

Include Files	Libraries
hil.h	hil.lib;quanser_runtime.lib;quanser_common.lib

Examples


/*
* Reads 5000 samples at 1 kHz from the first four digital input channels, using SYSTEM_CLOCK_1.
*/

t_uint32 channels[] = { 0, 1, 2, 3 };
t_double frequency  = 1000;
t_uint32 samples    = 5000;

static t_boolean buffer[5000][4];
t_error result = hil_read_digital_buffer(board, SYSTEM_CLOCK_1, frequency, samples,
                                         channels, ARRAY_LENGTH(channels), &buffer[0][0]);

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