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pwm.md

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NAME

PWM module for Linux userspace sysfs PWMs.

SYNOPSIS

local periphery = require('periphery')
local PWM = periphery.PWM

-- Constructor
pwm = PWM(chip <number>, channel <number>)
pwm = PWM{chip=<number>, channel=<number>}

-- Methods
pwm:enable()
pwm:disable()
pwm:close()

-- Properties
pwm.enabled         mutable <boolean>
pwm.period_ns       mutable <number>
pwm.duty_cycle_ns   mutable <number>
pwm.period          mutable <number>
pwm.duty_cycle      mutable <number>
pwm.frequency       mutable <number>
pwm.polarity        mutable <string>
pwm.chip            immutable <number>
pwm.channel         immutable <number>

CONSTANTS

  • PWM Polarity
    • "normal" - Normal polarity
    • "reversed" - Reversed polarity

DESCRIPTION

PWM(chip <number>, channel <number>) --> <PWM object>
PWM{chip=<number>, channel=<number>} --> <PWM object>

Instantiate an LED object and open the sysfs PWM with the specified chip and channel.

Example:

-- Open PWM chip 0, channel 10
pwm = PWM(0, 10)
pwm = PWM{chip=0, channel=10}

Returns a new PWM object on success. Raises a PWM error on failure.

pwm:enable()

Enable the PWM output.

Raises a PWM error on failure.

pwm:disable()

Disable the PWM output.

Raises a PWM error on failure.

pwm:close()

Close the PWM.

Raises a PWM error on failure.

Property pwm.enabled        mutable <boolean>

Get or set the output state of the PWM.

Raises a PWM error on failure.

Property pwm.period_ns      mutable <number>
Property pwm.duty_cycle_ns  mutable <number>

Get or set the period in nanoseconds or duty cycle in nanoseconds, respectively, of the PWM.

Raises a PWM error on failure.

Property pwm.period         mutable <number>
Property pwm.duty_cycle     mutable <number>
Property pwm.frequency      mutable <number>

Get or set the period in seconds, duty cycle as a ratio between 0.0 to 1.0, or frequency in Hz, respectively, of the PWM.

Raises a PWM error on failure.

Proprety pwm.polarity       mutable <string>

Get or set the output polarity of the PWM. Can be "normal" or "inversed" (see constants above).

Raises a PWM error on failure or on assignment with an invalid polarity.

Property pwm.chip           immutable <number>

Get the chip number of the PWM object.

Raises a PWM error on assignment.

Property pwm.channel        immutable <number>

Get the channel number of the PWM object.

Raises a PWM error on assignment.

ERRORS

The periphery PWM methods and properties may raise a Lua error on failure that can be propagated to the user or caught with Lua's pcall(). The error object raised is a table with code, c_errno, message properties, which contain the error code string, underlying C error number, and a descriptive message string of the error, respectively. The error object also provides the necessary metamethod for it to be formatted if it is propagated to the user by the interpreter.

--- Example of error propagated to user
> periphery = require('periphery')
> pwm = periphery.PWM(0, 10)
Opening PWM: opening 'export': Permission denied [errno 13]
> 

--- Example of error caught with pcall()
> status, err = pcall(function () pwm = periphery.PWM(0, 10) end)
> =status
false
> dump(err)
{
  c_errno = 13,
  message = "Opening PWM: opening 'export': Permission denied [errno 13]",
  code = "PWM_ERROR_OPEN"
}
>
Error Code Description
"PWM_ERROR_ARG" Invalid arguments
"PWM_ERROR_OPEN" Opening PWM
"PWM_ERROR_QUERY" Querying PWM attributes
"PWM_ERROR_CONFIGURE" Configuring PWM attributes
"PWM_ERROR_CLOSE" Closing PWM

EXAMPLE

local PWM = require('periphery').PWM

-- Open PWM chip 0, channel 10
local pwm = PWM(0, 10)

-- Set frequency to 1 kHz
pwm.frequency = 1e3
-- Set duty cycle to 75%
pwm.duty_cycle = 0.75

-- Enable PWM output
pwm:enable()

pwm:close()