hil_task_create_encoder_reader_pwm_writer

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Creates a task for reading from encoder inputs and writing to PWM outputs at the same time.

Description

The hil_task_create_encoder_reader_pwm_writer function creates a task for reading from the specified encoder input channels and writing to the specified PWM output channels at the same time. The task allows other operations to be performed while the encoder inputs are being read and the PWM outputs are being written "in the background". The data read from the encoder inputs is stored in an internal circular "task input buffer". The data written to the PWM outputs is read from an internal circular "task output buffer". The application may read the data from the task input buffer and write data to the task output buffer at any time using the hil_task_read_encoder_write_pwm function. Data may also be read separately from the task input buffer using the hil_task_read_encoder function, and data may also be written into the task output buffer using the hil_task_write_pwm function. The size of both the task input buffer and the task output buffer is determined by the samples_in_buffer parameter.

The hil_task_write_pwm function is typically called prior to starting the task in order to put the initial samples in the the task output buffer. After the task is started, hil_task_read_encoder_write_pwm is typically called to read the encoder input values from the task input buffer and to put more data into the task output buffer for the PWM outputs.

The task does not actually start reading from the encoder inputs and storing the data in the task input buffer or reading the data from the task output buffer and writing it to the PWM outputs until the hil_task_start function is called. In order for data to be available in the task buffer as soon as the task starts, store data in the buffer using hil_task_write_pwm prior to starting the task.

Each sampling instant, the task first reads from the encoder input channels selected and stores the data in the task input buffer. Then, in the same sampling instant, the task extracts one sample from the task output buffer and writes to the selected PWM output channels. This synchronization of input and output is particularly useful for system identification because the time at which a sample is read and a sample is written is known, so no postprocessing is required to determine the response delay in the system been identified.

Since the task writes to the PWM outputs at the sampling rate specified when the task is started, it will be reading data from the task output buffer at that rate. Thus, hil_task_read_encoder_write_pwm or hil_task_write_pwm must be called to add more data to the task output buffer before all the data in the buffer is depleted. Otherwise the task will have no data to write to the PWM outputs and will return with a QERR_BUFFER_OVERFLOW error the next time hil_task_read_encoder_write_pwm or hil_task_write_pwm is called.

The task must be deleted when it is no longer in use using the hil_task_delete function, in order to free the system and hardware resources used by the task. See Tasks for more information on tasks.

Prototype

t_error 
hil_task_create_encoder_reader_pwm_writer(t_card card, t_uint32 samples_in_buffer,
                                          const t_uint32 encoder_input_channels[], t_uint32 num_encoder_input_channels,
                                          const t_uint32 pwm_output_channels[],    t_uint32 num_pwm_output_channels,
                                          t_task *task);

Parameters

t_card card

A handle to the board, as returned by hil_open.

t_uint32 samples_in_buffer

The number of samples in the task buffers. The hil_task_read_encoder_write_pwm function cannot read or write more samples than this in a single call. If the task input buffer overflows because hil_task_read_encoder_write_pwm has not been called in time to remove data from the task input buffer then the next call to hil_task_read_encoder_write_pwm will return an HIL_BUFFER_OVERFLOW error. Likewise, if the task output buffer underflows because hil_task_read_encoder_write_pwm has not been called in time to add data to the task output buffer then the next call to hil_task_read_encoder_write_pwm will also return an HIL_BUFFER_OVERFLOW error. See Tasks for more information on task buffers.

const t_uint32 [] encoder_input_channels

An array containing the channel numbers of the encoder inputs to be read by the task.

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

t_uint32 num_encoder_input_channels

The number of channels specified in the encoder_input_channels array.

const t_uint32 [] pwm_output_channels

An array containing the channel numbers of the PWM outputs to be written to by the task.

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

t_uint32 num_pwm_output_channels

The number of channels specified in the pwm_output_channels array.

t_task * task

A handle to the task is returned in the t_task variable passed in this parameter. This argument cannot be NULL. Pass the address of a variable of type t_task.

Return value

The return value is 0 if the task is created successfully. 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_TASK_CREATE_ENCODER_READER_PWM_WRITER_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_TASK_ARGUMENT_IS_NULL

The task argument is NULL. A pointer to a t_task variable must be supplied because this variable must be passed to the other HIL task functions to refer to the task.

QERR_MISSING_ENCODER_INPUTS

The encoder input channels argument is NULL when the number of encoder inputs specified is non-zero.

QERR_TOO_MANY_ENCODER_INPUT_CHANNELS

Too many encoder input channels were specified.

QERR_INVALID_ENCODER_INPUT_CHANNEL

One of the encoder 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_ENCODER_INPUT_CHANNELS_NOT_SUPPORTED

Encoder input channels are not supported by this board.

QERR_MISSING_PWM_OUTPUTS

The PWM output channels argument is NULL when the number of PWM outputs specified is non-zero.

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_PWM_OUTPUT_CHANNELS_NOT_SUPPORTED

PWM output channels are not supported by this board.

QERR_INVALID_BOARD_HANDLE

An invalid board handle was passed as an argument to the board-specific HIL driver. Once a card has been closed using hil_close the board handle is invalid.

QERR_INVALID_BUFFER_HANDLE

An invalid buffer handle was passed to a board-specific HIL driver function.

QERR_OPERATION_ARGUMENT_IS_NULL

The operation argument to a board-specific HIL driver is NULL. This situation should never occur unless the user is calling the board-specific driver directly or memory has been corrupted.

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 encoder input channels 2 and 3 while writing at the same time
* to PWM output channels 0 and 1, using SYSTEM_CLOCK_1. Return values are ignored for simplicity.
*/

t_uint32 input_channels[]      = { 2, 3 };
t_uint32 output_channels[]     = { 0, 1 };
t_double frequency             = 1000;
t_uint32 samples               = 5000;
t_uint32 samples_in_buffer     = frequency;
t_uint32 samples_to_read_write = 1;

static t_int32  input_buffer[2];
static t_double output_buffer[2];
t_task task;

/* Fill output buffer */
...
hil_task_create_encoder_reader_pwm_writer(board, samples_in_buffer,
     input_channels,  ARRAY_LENGTH(input_channels), 
     output_channels, ARRAY_LENGTH(output_channels), 
     &task);
hil_task_write_pwm(task, samples_to_read_write, output_buffer); /* pre-fill the task output buffer prior to starting the task */
hil_task_start(task, SYSTEM_CLOCK_1, frequency, samples);
for (int index = 0; index < samples; index += samples_to_read_write) {
    /* Fill output buffer */
    ...
    hil_task_read_encoder_write_pwm(task, samples_to_write, input_buffer, output_buffer); /* waits for data to be read from hardware */
    ...                                                                                   /* and for space in the task output buffer */
}
hil_task_stop(task);
hil_task_delete(task);

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