hil_read_digital_write_digital_buffer

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Reads the specified number of samples from the digital input channels and writes the specified number of samples to the digital output channels at the indicated sampling rate.

Description

The hil_read_digital_write_digital_buffer function reads the specified number of samples from the digital input channels and writes to the specified digital output channels at the given sampling rate in a single function call. Each sampling instant, the write operation occurs immediately following the read operation. Since the read-write operation occurs at the lowest level the read and write occur virtually concurrently. The function does not return until all the data has been read and written. This function is particularly useful for system identification since the read and write operations are synchronized. In particular, the value read in one sampling instant is the result of the write operation in the previous sampling instant. See the Buffered I/O overview for more details.

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 or outputs must be configured accordingly using this function. Failure to configure the digital I/O may result in the hil_read_digital_write_digital_buffer function failing to read or write the digital I/O as expected.

Prototype

t_error 
hil_read_digital_write_digital_buffer(t_card card, t_clock clock, t_double frequency, t_uint32 num_samples,
                                      const t_uint32  digital_input_channels[],  t_uint32 num_digital_input_channels, 
                                      const t_uint32  digital_output_channels[], t_uint32 num_digital_output_channels, 
                                      t_boolean       digital_input_buffer[],
                                      const t_boolean digital_output_buffer[]);

Parameters

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 read from the digital input channels and write to the digital output channels. For example, if frequency is set to 1000, then the hil_read_digital_write_digital_buffer function will read all the input channels and write all the output channels every millisecond.

t_uint32 num_samples

The number of samples to process. Each "sample" consists of all the digital input channels and all the digital output channel specified. For example, if frequency is set to 1000 and num_samples is set to 5000, then the hil_read_digital_write_digital_buffer function will return after 5 seconds, having read 5000 samples and written 5000 samples. If 3 input channels have been selected, then the input buffer will contain 15,000 elements. If 2 output channels have been selected, then the output buffer must contain 10,000 elements.

const t_uint32 [] digital_input_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_digital_input_channels

The number of channels specified in the digital_input_channels array.

const t_uint32 [] digital_output_channels

An array containing the channel numbers of the digital outputs to which to write.

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

t_uint32 num_digital_output_channels

The number of channels specified in the digital_output_channels array.

t_boolean [] digital_input_buffer

An array for receiving the binary values read from the digital inputs. The array must contain num_digital_input_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].

const t_boolean [] digital_output_buffer

An array containing the binary values to write to the digital outputs. The array must contain num_digital_output_channels * num_samples elements. The array must be organized as a linear array of samples, with each sample consisting of a group of channels. Refer to the digital_input_buffer parameter for an example.

Return value

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

Error codes

QERR_HIL_READ_DIGITAL_WRITE_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_TOO_MANY_DIGITAL_OUTPUT_CHANNELS

Too many digital output channels were specified.

QERR_INVALID_DIGITAL_OUTPUT_CHANNEL

One of the digital output 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 and writes at the same time
* to the digital output channels 5 and 6, using SYSTEM_CLOCK_1.
*/

t_double frequency = 1000;
t_uint32 samples   = 5000;
t_error result;
int i, j;

t_uint32 input_channels[]  = { 0, 1, 2, 3 };
t_uint32 output_channels[] = { 5, 6 };

static t_boolean input_buffer[5000][4];
static t_boolean output_buffer[5000][2];

for (i=0; i < samples; i++) {
    double time = i / frequency;
    for (j=0; j < ARRAY_LENGTH(output_channels); j++)
        output_buffer[i][j] = (i % (j + 2)) >= (j + 2)/2;
}

result = hil_read_digital_write_digital_buffer(board, SYSTEM_CLOCK_1, frequency, samples
    , input_channels,  ARRAY_LENGTH(input_channels)
    , output_channels, ARRAY_LENGTH(output_channels)
    , &input_buffer[0][0]
    , &output_buffer[0][0]
);

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