eLua platform interface - PWM

Overview

This part of the platform interface groups functions related to the PWM channel(s) of the MCU.

Data structures, constants and types

// PWM operations
enum
{
  PLATFORM_PWM_OP_START,
  PLATFORM_PWM_OP_STOP,
  PLATFORM_PWM_OP_SET_CLOCK,
  PLATFORM_PWM_OP_GET_CLOCK
}

This enum lists all the operations that can be executed on a given PWM channel.

Functions

platform_pwm_exists platform_pwm_setup platform_pwm_op

int platform_pwm_exists( unsigned id );

Checks if the platform has the PWM channel specified as argument. Implemented in src/common.c, it uses the NUM_PWM macro that must be defined in the platform's platform_conf.h file (see here for details). For example:

#define NUM_PWM   4      // The platform has 4 PWM channels

Arguments: id - PWM channel ID

Returns: 1 if the specified PWM channel exists, 0 otherwise

u32 platform_pwm_setup( unsigned id, u32 frequency, unsigned duty );

Sets up a PWM channel

Arguments:

  • id - PWM channel ID
  • frequency - PWM channel frequency (in hertz)
  • duty - PWM channel duty cycle, specified as percent (from 0 to 100). Note that some platform don't allow the full 0-100 duty cycle

Returns: The actual frequency set on the PWM channel, which might differ from the frequency parameter, depeding on the hardware

u32 platform_pwm_op( unsigned id, int op, u32 data );

Executes an operation on a PWM channel

Arguments:

  • id - PWM channel ID
  • op - the operation that must be executed. It can take any value from this enum, as follows:
    • PLATFORM_PWM_OP_START: starts PWM generation on the specified channel.
    • PLATFORM_PWM_OP_STOP: stops PWM generation on the specified channel.
    • PLATFORM_PWM_OP_SET_CLOCK: sets the base clock of the specified PWM channel (which will be used to generate the frequencies requested by platform_pwm_setup) to data hertz.
    • PLATFORM_PWM_OP_GET_CLOCK: get the base clock of the specified PWM channel.
  • data - when used with op == PLATFORM_PWM_OP_SET_CLOCK it is used to specify the value of the base clock. Not used with other operations.

Returns:

  • the actual value of the base clock when op == PLATFORM_PWM_OP_SET_CLOCK, which might be different than data depending on the hardware
  • the value of the base clock when op == PLATFORM_PWM_OP_GET_CLOCK
  • irellevant for other operations