hil_write_pwm_buffer :: Quanser C Functions

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hil_write_pwm_buffer

Writes the specified number of samples to the PWM channels at the indicated sampling rate.

Description

The hil_write_pwm_buffer function writes the specified number of samples to the PWM output channels at the given sampling rate. The function does not return until the data has been written.

The interpretation of the data to be written depends upon the PWM mode. Typically the data is interpreted as a duty cycle, in which a magnitude of 0.0 denotes a 0% duty cycle and magnitude of 1.0 indicates a 100% duty cycle. The sign determines the polarity of the output for those boards supporting bidirectional PWM outputs. However, other PWM modes are possible with some boards. Refer to the hil_set_pwm_mode function for details.

Prototype

t_error 
hil_write_pwm_buffer(t_card card, t_clock clock, t_double frequency, t_uint32 num_samples,
                     const t_uint32 pwm_channels[], t_uint32 num_channels, const t_double 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 write to the PWM output channels. For example, if frequency is set to 1000, then the hil_write_pwm_buffer function will write to all the selected channels every millisecond.

t_uint32 num_samples

The number of samples to generate. Each "sample" consists of all the PWM output channels specified. For example, if frequency is set to 1000 and num_samples is set to 5000, then the hil_write_pwm_buffer function will return after 5 seconds, having written 5000 samples. If 3 channels have been selected, then the buffer must therefore contain 15,000 elements.

const t_uint32 [] pwm_channels

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

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

t_uint32 num_channels

The number of channels specified in the pwm_channels array.

const t_double [] buffer

An array containing the values to write to the PWM outputs. How these values are interpreted depends on the PWM mode. The PWM mode is configured using the hil_set_pwm_mode function. The array must contain num_channels * num_samples elements. The array must be organized as a linear array of samples, with each sample consisting of a group of channels. For example, if pwm output channels 0, 1 and 3 are being written, than the data must appear in the array as follows, where the numbers correspond to channel numbers:

...

This ordering is equivalent to defining the buffer as:

t_double 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 samples successfully written. 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_WRITE_PWM_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_MISSING_PWM_OUTPUTS

The pwm_channels argument is NULL. If the number of channels is greater than zero then a channel vector must be provided.

QERR_MISSING_PWM_OUTPUT_BUFFER

The buffer argument is NULL. If the number of channels is greater than zero then a buffer must be provided.

QERR_TOO_MANY_PWM_OUTPUT_CHANNELS

Too many PWM output channels were specified.

QERR_INVALID_PWM_OUTPUT_CHANNEL

One of the PWM 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_HARDWARE_CLOCK_IN_USE

The specified hardware clock is already in use for another operation and the board-specific HIL driver for this board does not permit sharing of the hardware clock or one of the PWM output channels is based on a hardware clock that is already in use for another operation.

QERR_WRONG_CLOCK_MODE

One of the PWM output channels is based on a hardware clock that is in the wrong mode for this operation. Use the hil_set_clock_mode function to change modes.

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


/*
* Writes 5000 samples at 1 kHz to the first two PWM output channels, using SYSTEM_CLOCK_1.
*/

t_uint32 channels[] = { 0, 1 };
t_double frequency = 1000;
t_uint32 samples   = 5000;
t_error result;
int i, j;

static t_double buffer[5000][2];

for (i=0; i < samples; i++) {
    double time = i / frequency;
    for (j=0; j < ARRAY_LENGTH(channels); j++)
        buffer[i][j] = 0.5 + 0.5 * sin(2*M_PI*time);
}

result = hil_write_pwm_buffer(board, SYSTEM_CLOCK_1, frequency, samples,
                              channels, ARRAY_LENGTH(channels), &buffer[0][0]);

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