PWM

Description

C interface for the Sitara PWM driver.

<rc/pwm.h>

These functions provide a general interface to all 3 PWM subsystems, each of which have two available channels A and B. PWM subsystems 1 and 2 are used for controlling the 4 motor drivers on the Robotics Cape, however they may be controlled by the user directly instead of using the motor API. PWM subsystem 0 channels A and B can be accessed on the GPS header if set up with the Pinmux API to do so. The user may have exclusive use of that subsystem.

Author

James Strawson

Date

1/31/2018

Functions
int	rc_pwm_init (int ss, int frequency)
	Configures subsystem 0, 1, or 2 to operate at a particular frequency. More...
int	rc_pwm_cleanup (int ss)
	Stops a subsystem and puts it into a low-power state. More...
int	rc_pwm_set_duty (int ss, char ch, double duty)
	Sets the duty cycle of a specific pwm channel. More...
int	rc_pwm_set_duty_ns (int ss, char ch, unsigned int duty_ns)
	Like rc_pwm_set_duty() but takes a pulse width in nanoseconds. More...

Function Documentation

rc_pwm_init()

int rc_pwm_init	(	int	ss,
		int	frequency
	)

Configures subsystem 0, 1, or 2 to operate at a particular frequency.

This may be called at runtime to change the pwm frequency without stopping the motors or pwm signal.

Parameters

[in]	ss	Subsystem 0 1 or 2
[in]	frequency	The frequency in HZ

Returns

Returns 0 on success or -1 on failure.

rc_pwm_cleanup()

int rc_pwm_cleanup

(

int

ss

)

Stops a subsystem and puts it into a low-power state.

Recommended to call before userspace program exits to ensure the PWM hardware stops.

Parameters

[in]

ss

subsystem 0,1,2

Returns

Returns 0 on success or -1 on failure.

rc_pwm_set_duty()

int rc_pwm_set_duty	(	int	ss,
		char	ch,
		double	duty
	)

Sets the duty cycle of a specific pwm channel.

Parameters

[in]	ss	subsystem 0,1,2
[in]	ch	channel 'A' or 'B'
[in]	duty	between 0.0 (off) and 1.0(full on)

Returns

Returns 0 on success or -1 on failure.

rc_pwm_set_duty_ns()

int rc_pwm_set_duty_ns	(	int	ss,
		char	ch,
		unsigned int	duty_ns
	)

Like rc_pwm_set_duty() but takes a pulse width in nanoseconds.

duty_ns which must range from 0 (off) to the number of nanoseconds in a single cycle as determined by the freqency specified when calling rc_pwm_init(). For example, a pwm frequency of 25kz corresponds to a maximum pulse width of 40,000ns.

Parameters

[in]	ss	subsystem 0,1,2
[in]	ch	channel 'A' or 'B'
[in]	duty_ns	The duty cycle (pulse width) in nanoseconds

Returns

Returns 0 on success or -1 on failure.