gpio

Documentation

Overview

Package gpio defines digital pins.

All GPIO implementations are expected to implement PinIO but the device driver may accept a more specific one like PinIn or PinOut.

Example

package main

import (
	"fmt"
	"log"

	"periph.io/x/periph/conn/gpio/gpioreg"
	"periph.io/x/periph/host"
)

func main() {
	// Make sure periph is initialized.
	if _, err := host.Init(); err != nil {
		log.Fatal(err)
	}

	// Use gpioreg GPIO pin registry to find a GPIO pin by name.
	p := gpioreg.ByName("GPIO6")
	if p == nil {
		log.Fatal("Failed to find GPIO6")
	}

	// A pin can be read, independent of its state; it doesn't matter if it is
	// set as input or output.
	fmt.Printf("%s is %s\n", p, p.Read())
}

Index

• Constants
• type Duty
  • func ParseDuty(s string) (Duty, error)
  • func (d Duty) String() string
  • func (d Duty) Valid() bool
• type Edge
  • func (i Edge) String() string
• type Level
  • func (l Level) String() string
• type PinIO
• type PinIn
• type PinOut
• type Pull
  • func (i Pull) String() string
• type RealPin

Examples

• Package
• ParseDuty
• PinIn
• PinOut
• RealPin

Constants

const (
	// Inputs
	IN      pin.Func = "IN"      // Input
	IN_HIGH pin.Func = "In/High" // Read high
	IN_LOW  pin.Func = "In/Low"  // Read low

	// Outputs
	OUT      pin.Func = "OUT"      // Output, drive
	OUT_OC   pin.Func = "OUT_OPEN" // Output, open collector/drain
	OUT_HIGH pin.Func = "Out/High" // Drive high
	OUT_LOW  pin.Func = "Out/Low"  // Drive low; open collector low

	FLOAT pin.Func = "FLOAT" // Input float or Output open collector high

	CLK pin.Func = "CLK" // Clock is a subset of a PWM, with a 50% duty cycle
	PWM pin.Func = "PWM" // Pulse Width Modulation, which is a clock with variable duty cycle
)

Types

type Duty

type Duty int32

Duty is the duty cycle for a PWM.

Valid values are between 0 and DutyMax.

const (
	// DutyMax is a duty cycle of 100%.
	DutyMax Duty = 1 << 24
	// DutyHalf is a 50% duty PWM, which boils down to a normal clock.
	DutyHalf Duty = DutyMax / 2
)

func ParseDuty

func ParseDuty(s string) (Duty, error)

ParseDuty parses a string and converts it to a Duty value.

Example

package main

import (
	"fmt"
	"log"

	"periph.io/x/periph/conn/gpio"
)

func main() {
	d, err := gpio.ParseDuty("33%")
	if err != nil {
		log.Fatal(err)
	}
	fmt.Println(d)
}

Output:

33%

func (Duty) String

func (d Duty) String() string

func (Duty) Valid

func (d Duty) Valid() bool

Valid returns true if the Duty cycle value is valid.

type Edge

type Edge int

Edge specifies if an input pin should have edge detection enabled.

Only enable it when needed, since this causes system interrupts.

const (
	NoEdge      Edge = 0
	RisingEdge  Edge = 1
	FallingEdge Edge = 2
	BothEdges   Edge = 3
)

Acceptable edge detection values.

func (Edge) String

func (i Edge) String() string

type Level

type Level bool

Level is the level of the pin: Low or High.

const (
	// Low represents 0v.
	Low Level = false
	// High represents Vin, generally 3.3v or 5v.
	High Level = true
)

func (Level) String

func (l Level) String() string

type PinIO

type PinIO interface {
	pin.Pin
	// PinIn
	In(pull Pull, edge Edge) error
	Read() Level
	WaitForEdge(timeout time.Duration) bool
	Pull() Pull
	DefaultPull() Pull
	// PinOut
	Out(l Level) error
	PWM(duty Duty, f physic.Frequency) error
}

PinIO is a GPIO pin that supports both input and output. It matches both interfaces PinIn and PinOut.

A GPIO pin implementing PinIO may fail at either input or output or both.

var INVALID PinIO

INVALID implements PinIO and fails on all access.

type PinIn

type PinIn interface {
	pin.Pin
	// In setups a pin as an input.
	//
	// If WaitForEdge() is planned to be called, make sure to use one of the Edge
	// value. Otherwise, use NoEdge to not generated unneeded hardware interrupts.
	//
	// Calling In() will try to empty the accumulated edges but it cannot be 100%
	// reliable due to the OS (linux) and its driver. It is possible that on a
	// gpio that is as input, doing a quick Out(), In() may return an edge that
	// occurred before the Out() call.
	In(pull Pull, edge Edge) error
	// Read return the current pin level.
	//
	// Behavior is undefined if In() wasn't used before.
	//
	// In some rare case, it is possible that Read() fails silently. This happens
	// if another process on the host messes up with the pin after In() was
	// called. In this case, call In() again.
	Read() Level
	// WaitForEdge() waits for the next edge or immediately return if an edge
	// occurred since the last call.
	//
	// Only waits for the kind of edge as specified in a previous In() call.
	// Behavior is undefined if In() with a value other than NoEdge wasn't called
	// before.
	//
	// Returns true if an edge was detected during or before this call. Return
	// false if the timeout occurred or In() was called while waiting, causing the
	// function to exit.
	//
	// Multiple edges may or may not accumulate between two calls to
	// WaitForEdge(). The behavior in this case is undefined and is OS driver
	// specific.
	//
	// It is not required to call Read() to reset the edge detection.
	//
	// Specify -1 to effectively disable timeout.
	WaitForEdge(timeout time.Duration) bool
	// Pull returns the internal pull resistor if the pin is set as input pin.
	//
	// Returns PullNoChange if the value cannot be read.
	Pull() Pull
	// DefaultPull returns the pull that is initialized on CPU/device reset. This
	// is useful to determine if the pin is acceptable for operation with
	// certain devices.
	DefaultPull() Pull
}

PinIn is an input GPIO pin.

It may optionally support internal pull resistor and edge based triggering.

A button is semantically a PinIn. So if you are looking to read from a button, PinIn is the interface you are looking for.

Example

package main

import (
	"fmt"
	"log"

	"periph.io/x/periph/conn/gpio"
	"periph.io/x/periph/conn/gpio/gpioreg"
	"periph.io/x/periph/host"
)

func main() {
	// Make sure periph is initialized.
	if _, err := host.Init(); err != nil {
		log.Fatal(err)
	}

	// Use gpioreg GPIO pin registry to find a GPIO pin by name.
	p := gpioreg.ByName("GPIO6")
	if p == nil {
		log.Fatal("Failed to find GPIO6")
	}

	// Set it as input, with a pull down (defaults to Low when unconnected) and
	// enable rising edge triggering.
	if err := p.In(gpio.PullDown, gpio.RisingEdge); err != nil {
		log.Fatal(err)
	}
	fmt.Printf("%s is %s\n", p, p.Read())

	// Wait for rising edges (Low -> High) and print when one occur.
	for p.WaitForEdge(-1) {
		fmt.Printf("%s went %s\n", p, gpio.High)
	}
}

type PinOut

type PinOut interface {
	pin.Pin
	// Out sets a pin as output if it wasn't already and sets the initial value.
	//
	// After the initial call to ensure that the pin has been set as output, it
	// is generally safe to ignore the error returned.
	//
	// Out() tries to empty the accumulated edges detected if the gpio was
	// previously set as input but this is not 100% guaranteed due to the OS.
	Out(l Level) error
	// PWM sets the PWM output on supported pins, if the pin has hardware PWM
	// support.
	//
	// To use as a general purpose clock, set duty to DutyHalf. Some pins may
	// only support DutyHalf and no other value.
	//
	// Using 0 as frequency will use the optimal value as supported/preferred by
	// the pin.
	//
	// To use as a servo, see https://en.wikipedia.org/wiki/Servo_control as an
	// explanation how to calculate duty.
	PWM(duty Duty, f physic.Frequency) error
}

PinOut is an output GPIO pin.

A LED, a buzzer, a servo, are semantically a PinOut. So if you are looking to control these, PinOut is the interface you are looking for.

Example

package main

import (
	"log"

	"periph.io/x/periph/conn/gpio"
	"periph.io/x/periph/conn/gpio/gpioreg"
	"periph.io/x/periph/host"
)

func main() {
	// Make sure periph is initialized.
	if _, err := host.Init(); err != nil {
		log.Fatal(err)
	}

	// Use gpioreg GPIO pin registry to find a GPIO pin by name.
	p := gpioreg.ByName("GPIO6")
	if p == nil {
		log.Fatal("Failed to find GPIO6")
	}

	// Set the pin as output High.
	if err := p.Out(gpio.High); err != nil {
		log.Fatal(err)
	}
}

type Pull

type Pull uint8

Pull specifies the internal pull-up or pull-down for a pin set as input.

const (
	PullNoChange Pull = 0 // Do not change the previous pull resistor setting or an unknown value
	Float        Pull = 1 // Let the input float
	PullDown     Pull = 2 // Apply pull-down
	PullUp       Pull = 3 // Apply pull-up
)

Acceptable pull values.

func (Pull) String

func (i Pull) String() string

type RealPin

type RealPin interface {
	Real() PinIO // Real returns the real pin behind an Alias
}

RealPin is implemented by aliased pin and allows the retrieval of the real pin underlying an alias.

Aliases are created by RegisterAlias. Aliases permits presenting a user friendly GPIO pin name while representing the underlying real pin.

The purpose of the RealPin is to be able to cleanly test whether an arbitrary gpio.PinIO returned by ByName is an alias for another pin, and resolve it.

Example

package main

import (
	"fmt"
	"log"

	"periph.io/x/periph/conn/gpio"
	"periph.io/x/periph/conn/gpio/gpioreg"
	"periph.io/x/periph/host"
)

func main() {
	// Make sure periph is initialized.
	if _, err := host.Init(); err != nil {
		log.Fatal(err)
	}

	// Use gpioreg GPIO pin registry to find a GPIO pin by name.
	p := gpioreg.ByName("P1_3")
	if p == nil {
		log.Fatal("Failed to find P1_3")
	}
	fmt.Printf("P1_3: %s", p)

	// Resolve the real underlying pin.
	if r, ok := p.(gpio.RealPin); ok {
		// On Raspberry Pis, pin #3 on header P1 is an alias for GPIO2.
		fmt.Printf("%s is in fact %s", p, r.Real())
	} else {
		log.Printf("%s is not an alias", p)
	}
}