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github.com/kidoman/embd

package embd

v0.0.0 (d3d8c0c)
Latest Go to latest
Published: May 8, 2017 | License: MIT | Module: github.com/kidoman/embd

Overview

Package embd provides a hardware abstraction layer for doing embedded programming on supported platforms like the Raspberry Pi, BeagleBone Black and CHIP. Most of the examples below will work without change (i.e. the same binary) on all supported platforms.

== Overall structure

It's best to think of the top-level embd package as a switchboard that doesn't implement anything on its own but rather relies on sub-packages for hosts drivers and devices and stitches them together. The exports in the top-level package serve a number of different purposes, which can be confusing at first: - it defines a number of driver interfaces, such as the GPIODriver, this is the interface that the driver for each specific platform must implement and is not something of concern to the typical user. - it defines the main low-level hardware interface types: analog pins, digital pins, interrupt pins, I2Cbuses, SPI buses, PWM pins and LEDs. Each type has a New function to instantiate one of these pins or buses. - it defines a number of InitXXX functions that initialize the various drivers, however, these are called by the coresponding NewXXX functions, so can be ignored. - it defines a number of top-level convenience functions, such as DigitalWrite, that can be called as 1-liners instead of first instantiating a DigitalPin and then writing to it

To get started a host driver needs to be registered with the top-level embd package. This is most easily accomplished by doing an "underscore import" on of the sub-packages of embd/host, e.g., `import _ "github.com/kidoman/embd/host/chip"`. An `Init()` function in the host driver registers all the individual drivers with embd.

After getting the host driver the next step might be to instantiate a GPIO pin using `NewDigitalPin` or an I2CBus using `NewI2CBus`. Such a pin or bus can be used directly but often it is passed into the initializer of a sensor, controller or other user-level driver which provides a high-level interface to some device. For example, the New function for the BMP180 type in the `embd/sensor/bmp180` package takes an I2CBus as argument, which it will use to reach the sensor.

== Samples

This section shows a few choice samples, more are available in the samples folder.

Use the LED driver to toggle LEDs on the BBB:

import "github.com/kidoman/embd"
...
embd.InitLED()
defer embd.CloseLED()
...
led, err := embd.NewLED("USR3")
...
led.Toggle()

Even shorter while prototyping:

import "github.com/kidoman/embd"
...
embd.InitLED()
defer embd.CloseLED()
...
embd.ToggleLED(3)

BBB + PWM:

import "github.com/kidoman/embd"
...
embd.InitGPIO()
defer embd.CloseGPIO()
...
pwm, _ := embd.NewPWMPin("P9_14")
defer pwm.Close()
...
pwm.SetDuty(1000)

Control GPIO pins on the RaspberryPi / BeagleBone Black:

import "github.com/kidoman/embd"
...
embd.InitGPIO()
defer embd.CloseGPIO()
...
embd.SetDirection(10, embd.Out)
embd.DigitalWrite(10, embd.High)

Could also do:

import "github.com/kidoman/embd"
...
embd.InitGPIO()
defer embd.CloseGPIO()
...
pin, err := embd.NewDigitalPin(10)
...
pin.SetDirection(embd.Out)
pin.Write(embd.High)

Or read data from the Bosch BMP085 barometric sensor:

import "github.com/kidoman/embd"
import "github.com/kidoman/embd/sensor/bmp085"
...
bus := embd.NewI2CBus(1)
...
baro := bmp085.New(bus)
...
temp, err := baro.Temperature()
altitude, err := baro.Altitude()

Even find out the heading from the LSM303 magnetometer:

import "github.com/kidoman/embd"
import "github.com/kidoman/embd/sensor/lsm303"
...
bus := embd.NewI2CBus(1)
...
mag := lsm303.New(bus)
...
heading, err := mag.Heading()

The above two examples depend on I2C and therefore will work without change on almost all platforms.

Index

Constants

const (
	// HostNull reprents a null host.
	HostNull Host = ""

	// HostRPi represents the RaspberryPi.
	HostRPi = "Raspberry Pi"

	// HostBBB represents the BeagleBone Black.
	HostBBB = "BeagleBone Black"

	// HostGalileo represents the Intel Galileo board.
	HostGalileo = "Intel Galileo"

	// HostCubieTruck represents the Cubie Truck.
	HostCubieTruck = "CubieTruck"

	// HostRadxa represents the Radxa board.
	HostRadxa = "Radxa"

	// HostCHIP represents the NextThing C.H.I.P.
	HostCHIP = "CHIP"
)
const (
	// Low represents 0.
	Low int = iota

	// High represents 1.
	High
)
const (
	// CapDigital represents the digital IO capability.
	CapDigital int = 1 << iota

	// CapI2C represents pins with the I2C capability.
	CapI2C

	// CapUART represents pins with the UART capability.
	CapUART

	// CapSPI represents pins with the SPI capability.
	CapSPI

	// CapGPMS represents pins with the GPMC capability.
	CapGPMC

	// CapLCD represents pins used to carry LCD data.
	CapLCD

	// CapPWM represents pins with PWM capability.
	CapPWM

	// CapAnalog represents pins with analog IO capability.
	CapAnalog
)
const (

	// SPIMode0 represents the mode0 operation (CPOL=0 CPHA=0) of spi.
	SPIMode0 = (0 | 0)

	// SPIMode1 represents the mode0 operation (CPOL=0 CPHA=1) of spi.
	SPIMode1 = (0 | spiCpha)

	// SPIMode2 represents the mode0 operation (CPOL=1 CPHA=0) of spi.
	SPIMode2 = (spiCpol | 0)

	// SPIMode3 represents the mode0 operation (CPOL=1 CPHA=1) of spi.
	SPIMode3 = (spiCpol | spiCpha)
)

Variables

var ErrFeatureNotImplemented = errors.New("embd: requested feature is not implemented")

ErrFeatureNotImplemented is returned when a particular feature is supported by the host but not implemented yet.

var ErrFeatureNotSupported = errors.New("embd: requested feature is not supported")

ErrFeatureNotSupported is returned when the host does not support a particular feature.

func ActiveLow

func ActiveLow(key interface{}, b bool) error

ActiveLow makes the pin active low. A low logical state is represented by a high state on the physical pin, and vice-versa.

func AnalogRead

func AnalogRead(key interface{}) (int, error)

AnalogWrite reads a value from the pin.

func CloseGPIO

func CloseGPIO() error

CloseGPIO releases resources associated with the GPIO driver.

func CloseI2C

func CloseI2C() error

CloseI2C releases resources associated with the I2C driver.

func CloseLED

func CloseLED() error

CloseLED releases resources associated with the LED driver.

func CloseSPI

func CloseSPI() error

CloseSPI releases resources associated with the SPI driver.

func DigitalRead

func DigitalRead(key interface{}) (int, error)

DigitalRead reads a value from the pin.

func DigitalWrite

func DigitalWrite(key interface{}, val int) error

DigitalWrite writes val to the pin.

func FindFirstMatchingFile

func FindFirstMatchingFile(glob string) (string, error)

FindFirstMatchingFile finds the first glob match in the filesystem. Inspiration: https://github.com/mrmorphic/hwio/blob/master/hwio.go#L451

func InitGPIO

func InitGPIO() error

InitGPIO initializes the GPIO driver.

func InitI2C

func InitI2C() error

InitI2C initializes the I2C driver.

func InitLED

func InitLED() error

InitLED initializes the LED driver.

func InitSPI

func InitSPI() error

InitSPI initializes the SPI driver.

func LEDOff

func LEDOff(key interface{}) error

LEDOff switches the LED off.

func LEDOn

func LEDOn(key interface{}) error

LEDOn switches the LED on.

func LEDToggle

func LEDToggle(key interface{}) error

LEDToggle toggles the LED.

func PullDown

func PullDown(key interface{}) error

PullDown pulls the pin down.

func PullUp

func PullUp(key interface{}) error

PullUp pulls the pin up.

func Register

func Register(host Host, describer Describer)

Register makes a host describer available by the provided host key. If Register is called twice with the same host or if describer is nil, it panics.

func SetDirection

func SetDirection(key interface{}, dir Direction) error

SetDirection sets the direction of the pin (in/out).

func SetHost

func SetHost(host Host, rev int)

SetHost overrides the host and revision no.

type AnalogPin

type AnalogPin interface {
	// N returns the logical GPIO number.
	N() int

	// Read reads the value from the pin.
	Read() (int, error)

	// Close releases the resources associated with the pin.
	Close() error
}

AnalogPin implements access to a analog IO capable GPIO pin.

func NewAnalogPin

func NewAnalogPin(key interface{}) (AnalogPin, error)

NewAnalogPin returns a AnalogPin interface which allows control over the analog GPIO pin.

type Describer

type Describer func(rev int) *Descriptor

The Describer type is a Descriptor provider.

type Descriptor

type Descriptor struct {
	GPIODriver func() GPIODriver
	I2CDriver  func() I2CDriver
	LEDDriver  func() LEDDriver
	SPIDriver  func() SPIDriver
}

Descriptor represents a host descriptor.

func DescribeHost

func DescribeHost() (*Descriptor, error)

DescribeHost returns the detected host descriptor. Can be overriden by calling SetHost though.

type DigitalPin

type DigitalPin interface {
	InterruptPin

	// N returns the logical GPIO number.
	N() int

	// Write writes the provided value to the pin.
	Write(val int) error

	// Read reads the value from the pin.
	Read() (int, error)

	// TimePulse measures the duration of a pulse on the pin.
	TimePulse(state int) (time.Duration, error)

	// SetDirection sets the direction of the pin (in/out).
	SetDirection(dir Direction) error

	// ActiveLow makes the pin active low. A low logical state is represented by
	// a high state on the physical pin, and vice-versa.
	ActiveLow(b bool) error

	// PullUp pulls the pin up.
	PullUp() error

	// PullDown pulls the pin down.
	PullDown() error

	// Close releases the resources associated with the pin.
	Close() error
}

DigitalPin implements access to a digital IO capable GPIO pin.

func NewDigitalPin

func NewDigitalPin(key interface{}) (DigitalPin, error)

NewDigitalPin returns a DigitalPin interface which allows control over the digital GPIO pin.

type Direction

type Direction int

The Direction type indicates the direction of a GPIO pin.

const (
	// In represents read mode.
	In Direction = iota

	// Out represents write mode.
	Out
)

type Edge

type Edge string

The Edge trigger for the GPIO Interrupt

const (
	EdgeNone    Edge = "none"
	EdgeRising  Edge = "rising"
	EdgeFalling Edge = "falling"
	EdgeBoth    Edge = "both"
)

type GPIODriver

type GPIODriver interface {
	// PinMap returns the pinmap for this driver.
	PinMap() PinMap

	// Unregister unregisters the pin from the driver. Should be called when the pin is closed.
	Unregister(string) error

	// DigitalPin returns a pin capable of doing digital IO.
	DigitalPin(key interface{}) (DigitalPin, error)

	// AnalogPin returns a pin capable of doing analog IO.
	AnalogPin(key interface{}) (AnalogPin, error)

	// PWMPin returns a pin capable of generating PWM.
	PWMPin(key interface{}) (PWMPin, error)

	// Close releases the resources associated with the driver.
	Close() error
}

GPIODriver implements a generic GPIO driver.

func NewGPIODriver

func NewGPIODriver(pinMap PinMap, dpf digitalPinFactory, apf analogPinFactory, ppf pwmPinFactory) GPIODriver

NewGPIODriver returns a GPIODriver interface which allows control over the GPIO subsystem.

type Host

type Host string

The Host type represents all the supported host types.

func DetectHost

func DetectHost() (host Host, rev int, err error)

DetectHost returns the detected host and its revision number.

type I2CBus

type I2CBus interface {
	// ReadByte reads a byte from the given address.
	ReadByte(addr byte) (value byte, err error)
	// ReadBytes reads a slice of bytes from the given address.
	ReadBytes(addr byte, num int) (value []byte, err error)
	// WriteByte writes a byte to the given address.
	WriteByte(addr, value byte) error
	// WriteBytes writes a slice bytes to the given address.
	WriteBytes(addr byte, value []byte) error

	// ReadFromReg reads n (len(value)) bytes from the given address and register.
	ReadFromReg(addr, reg byte, value []byte) error
	// ReadByteFromReg reads a byte from the given address and register.
	ReadByteFromReg(addr, reg byte) (value byte, err error)
	// ReadU16FromReg reads a unsigned 16 bit integer from the given address and register.
	ReadWordFromReg(addr, reg byte) (value uint16, err error)

	// WriteToReg writes len(value) bytes to the given address and register.
	WriteToReg(addr, reg byte, value []byte) error
	// WriteByteToReg writes a byte to the given address and register.
	WriteByteToReg(addr, reg, value byte) error
	// WriteU16ToReg
	WriteWordToReg(addr, reg byte, value uint16) error

	// Close releases the resources associated with the bus.
	Close() error
}

I2CBus interface is used to interact with the I2C bus.

func NewI2CBus

func NewI2CBus(l byte) I2CBus

NewI2CBus returns a I2CBus.

type I2CDriver

type I2CDriver interface {
	Bus(l byte) I2CBus

	// Close releases the resources associated with the driver.
	Close() error
}

I2CDriver interface interacts with the host descriptors to allow us control of I2C communication.

func NewI2CDriver

func NewI2CDriver(ibf i2cBusFactory) I2CDriver

NewI2CDriver returns a I2CDriver interface which allows control over the I²C subsystem.

type InterruptPin

type InterruptPin interface {

	// Start watching this pin for interrupt
	Watch(edge Edge, handler func(DigitalPin)) error

	// Stop watching this pin for interrupt
	StopWatching() error
}

InterruptPin implements access to an interrupt capable GPIO pin. The basic capability provided is to watch for a transition on the pin and generate a callback to a handler when a transition occurs. On Linux the underlying implementation generally uses epoll to receive the interrupts at user-level.

type LED

type LED interface {
	// On switches the LED on.
	On() error

	// Off switches the LED off.
	Off() error

	// Toggle toggles the LED.
	Toggle() error

	// Close releases resources associated with the LED.
	Close() error
}

The LED interface is used to control a led on the prototyping board.

func NewLED

func NewLED(key interface{}) (LED, error)

NewLED returns a LED interface which allows control over the LED.

type LEDDriver

type LEDDriver interface {
	LED(key interface{}) (LED, error)

	Close() error
}

LEDDriver interface interacts with the host descriptors to allow us control of the LEDs.

func NewLEDDriver

func NewLEDDriver(ledMap LEDMap, lf ledFactory) LEDDriver

NewLEDDriver returns a LEDDriver interface which allows control over the LED subsystem.

type LEDMap

type LEDMap map[string][]string

LEDMap type represents a LED mapping for a host.

type PWMPin

type PWMPin interface {
	// N returns the logical PWM id.
	N() string

	// SetPeriod sets the period of a pwm pin.
	SetPeriod(ns int) error

	// SetDuty sets the duty of a pwm pin.
	SetDuty(ns int) error

	// SetPolarity sets the polarity of a pwm pin.
	SetPolarity(pol Polarity) error

	// SetMicroseconds sends a command to the PWM driver to generate a us wide pulse.
	SetMicroseconds(us int) error

	// SetAnalog allows easy manipulation of the PWM based on a (0-255) range value.
	SetAnalog(value byte) error

	// Close releases the resources associated with the pin.
	Close() error
}

PWMPin implements access to a pwm capable GPIO pin.

func NewPWMPin

func NewPWMPin(key interface{}) (PWMPin, error)

NewPWMPin returns a PWMPin interface which allows PWM signal generation over a the PWM pin.

type PinDesc

type PinDesc struct {
	ID      string
	Aliases []string
	Caps    int

	DigitalLogical int
	AnalogLogical  int
}

PinDesc represents a pin descriptor.

type PinMap

type PinMap []*PinDesc

PinMap type represents a collection of pin descriptors.

func (PinMap) Lookup

func (m PinMap) Lookup(k interface{}, cap int) (*PinDesc, bool)

Lookup returns a pin descriptor matching the provided key and capability combination. This allows the same keys to be used across pins with differing capabilities. For example, it is perfectly fine to have:

pin1: {Aliases: [10, GPIO10], Cap: CapDigital}
pin2: {Aliases: [10, AIN0], Cap: CapAnalog}

Searching for 10 with CapDigital will return pin1 and searching for 10 with CapAnalog will return pin2. This makes for a very pleasant to use API.

type Polarity

type Polarity int

The Polarity type indicates the polarity of a pwm pin.

const (
	// Positive represents (default) positive polarity.
	Positive Polarity = iota

	// Negative represents negative polarity.
	Negative
)

type SPIBus

type SPIBus interface {
	io.Writer

	// TransferAndReceiveData transmits data in a buffer(slice) and receives into it.
	TransferAndReceiveData(dataBuffer []uint8) error

	// ReceiveData receives data of length len into a slice.
	ReceiveData(len int) ([]uint8, error)

	// TransferAndReceiveByte transmits a byte data and receives a byte.
	TransferAndReceiveByte(data byte) (byte, error)

	// ReceiveByte receives a byte data.
	ReceiveByte() (byte, error)

	// Close releases the resources associated with the bus.
	Close() error
}

SPIBus interface allows interaction with the SPI bus.

func NewSPIBus

func NewSPIBus(mode, channel byte, speed, bpw, delay int) SPIBus

NewSPIBus returns a SPIBus.

type SPIDriver

type SPIDriver interface {
	// Bus returns a SPIBus interface which allows us to use spi functionalities
	Bus(byte, byte, int, int, int) SPIBus

	// Close cleans up all the initialized SPIbus
	Close() error
}

SPIDriver interface interacts with the host descriptors to allow us control of SPI communication.

func NewSPIDriver

func NewSPIDriver(spiDevMinor int, sbf spiBusFactory, i func() error) SPIDriver

NewSPIDriver returns a SPIDriver interface which allows control over the SPI bus.

Documentation was rendered with GOOS=linux and GOARCH=amd64.

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