pwm.h File Reference

API Description

PWM is the Pulse Width Modulation interface to libmraa. It allows the generation of a signal on a pin. Some boards may have higher or lower levels of resolution so make sure you check the board & pin you are using before hand.

    pwm = mraa_pwm_init(PWM);
    if (pwm == NULL) {
        fprintf(stderr, "Failed to initialize PWM\n");
        mraa_deinit();
        return EXIT_FAILURE;
    }

    /* set PWM period */
    status = mraa_pwm_period_us(pwm, PWM_FREQ);
    if (status != MRAA_SUCCESS) {
        goto err_exit;
    }

    /* enable PWM */
    status = mraa_pwm_enable(pwm, 1);
    if (status != MRAA_SUCCESS) {
        goto err_exit;
    }

    while (flag) {
        value = value + 0.01f;

        /* write PWM duty cyle */
        status = mraa_pwm_write(pwm, value);
        if (status != MRAA_SUCCESS) {
            goto err_exit;
        }

        usleep(50000);

        if (value >= 1.0f) {
            value = 0.0f;
        }

        /* read PWM duty cyle */
        output = mraa_pwm_read(pwm);
        fprintf(stdout, "PWM value is %f\n", output);
    }

    /* close PWM */
    mraa_pwm_close(pwm);

Go to the source code of this file.

Functions
mraa_pwm_context	mraa_pwm_init (int pin)
mraa_pwm_context	mraa_pwm_init_raw (int chipid, int pin)
mraa_result_t	mraa_pwm_write (mraa_pwm_context dev, float percentage)
float	mraa_pwm_read (mraa_pwm_context dev)
mraa_result_t	mraa_pwm_period (mraa_pwm_context dev, float seconds)
mraa_result_t	mraa_pwm_period_ms (mraa_pwm_context dev, int ms)
mraa_result_t	mraa_pwm_period_us (mraa_pwm_context dev, int us)
mraa_result_t	mraa_pwm_pulsewidth (mraa_pwm_context dev, float seconds)
mraa_result_t	mraa_pwm_pulsewidth_ms (mraa_pwm_context dev, int ms)
mraa_result_t	mraa_pwm_pulsewidth_us (mraa_pwm_context dev, int us)
mraa_result_t	mraa_pwm_enable (mraa_pwm_context dev, int enable)
mraa_result_t	mraa_pwm_owner (mraa_pwm_context dev, mraa_boolean_t owner)
mraa_result_t	mraa_pwm_close (mraa_pwm_context dev)
int	mraa_pwm_get_max_period (mraa_pwm_context dev)
int	mraa_pwm_get_min_period (mraa_pwm_context dev)

Typedefs
typedef struct _pwm *	mraa_pwm_context

Function Documentation

mraa_pwm_context mraa_pwm_init

(

int

pin

)

Initialise pwm_context, uses board mapping

Parameters

pin	The PWM PIN

Returns

pwm context or NULL

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mraa_pwm_context mraa_pwm_init_raw	(	int	chipid,
		int	pin
	)

Initialise pwm_context, raw mode

Parameters

chipid	The chip inwhich the PWM is under in SYSFS
pin	The PWM PIN.

Returns

pwm context or NULL

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mraa_result_t mraa_pwm_write	(	mraa_pwm_context	dev,
		float	percentage
	)

Set the output duty-cycle percentage, as a float

Parameters

dev	The Pwm context to use
percentage	A floating-point value representing percentage of output. The value should lie between 0.0f (representing on 0%) and 1.0f Values above or below this range will be set at either 0.0f or 1.0f

Returns

Result of operation

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float mraa_pwm_read

(

mraa_pwm_context

dev

)

Read the output duty-cycle percentage, as a float

Parameters

dev	The Pwm context to use

Returns

percentage A floating-point value representing percentage of output. The value should lie between 0.0f (representing on 0%) and 1.0f Values above or below this range will be set at either 0.0f or 1.0f

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mraa_result_t mraa_pwm_period	(	mraa_pwm_context	dev,
		float	seconds
	)

Set the PWM period as seconds represented in a float

Parameters

dev	The Pwm context to use
seconds	Period represented as a float in seconds

Returns

Result of operation

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mraa_result_t mraa_pwm_period_ms	(	mraa_pwm_context	dev,
		int	ms
	)

Set period, milliseconds.

Parameters

dev	The Pwm context to use
ms	Milliseconds for period

Returns

Result of operation

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mraa_result_t mraa_pwm_period_us	(	mraa_pwm_context	dev,
		int	us
	)

Set period, microseconds

Parameters

dev	The Pwm context to use
us	Microseconds as period

Returns

Result of operation

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mraa_result_t mraa_pwm_pulsewidth	(	mraa_pwm_context	dev,
		float	seconds
	)

Set pulsewidth, As represnted by seconds in a (float)

Parameters

dev	The Pwm context to use
seconds	The duration of a pulse

Returns

Result of operation

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mraa_result_t mraa_pwm_pulsewidth_ms	(	mraa_pwm_context	dev,
		int	ms
	)

Set pulsewidth, milliseconds

Parameters

dev	The Pwm context to use
ms	Milliseconds for pulsewidth

Returns

Result of operation

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mraa_result_t mraa_pwm_pulsewidth_us	(	mraa_pwm_context	dev,
		int	us
	)

Set pulsewidth, microseconds

Parameters

dev	The Pwm context to use
us	Microseconds for pulsewidth

Returns

Result of operation

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mraa_result_t mraa_pwm_enable	(	mraa_pwm_context	dev,
		int	enable
	)

Set the enable status of the PWM pin. None zero will assume on with output being driven. and 0 will disable the output.

Parameters

dev	The pwm context to use
enable	Toggle status of pin

Returns

Result of operation.

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mraa_result_t mraa_pwm_owner	(	mraa_pwm_context	dev,
		mraa_boolean_t	owner
	)

Change ownership of context

Parameters

dev	the context
owner	Ownership boolean

Returns

Result of operation

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mraa_result_t mraa_pwm_close

(

mraa_pwm_context

dev

)

Close and unexport the PWM pin

Parameters

dev	The pwm context to use

Returns

Result of operation

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int mraa_pwm_get_max_period

(

mraa_pwm_context

dev

)

Get the maximum pwm period in us

Parameters

dev	The pwm context to use

Returns

max pwm in us

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int mraa_pwm_get_min_period

(

mraa_pwm_context

dev

)

Get the minimum pwm period in us

Parameters

dev	The pwm context to use

Returns

min pwm in us

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Typedef Documentation

typedef struct _pwm* mraa_pwm_context

Mraa Pwm Context

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