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package conn

import ""

Package conn defines core interfaces for protocols and connections.

This package and its subpackages describe the base interfaces to connect the software with the real world. It doesn't contain any implementation but includes registries to enable the application to discover the available hardware.


periph uses 3 layered concepts for interfacing:

Bus → Port → Conn

Not every subpackage expose all 3 concepts. In fact, most packages don't. For example, SPI doesn't expose Bus as the OSes generally only expose the Port, that is, a Chip Select (CS) line must be selected right upfront to get an handle. For I²C, there's no Port to configure, so selecting a "slave" address is sufficient to jump directly from a Bus to a Conn.

periph doesn't have yet a concept of star-like communication network, like an IP network.


A Bus is a multi-point communication channel where one "master" and multiple "slaves" communicate together. In the case of periph, the Bus handle is assumed to be the "master". The "master" generally initiates communications and selects the "slave" to talk to.

As the "master" selects a "slave" over a bus, a virtual Port is automatically created.

Examples include SPI, I²C and 1-wire. In each case, selecting a communication line (Chip Select (CS) line for SPI, address for I²C or 1-wire) converts the Bus into a Port.


A port is a point-to-point communication channel that is yet to be initialized. It cannot be used for communication until it is connected and transformed into a Conn. Configuring a Port converts it into a Conn. Not all Port need configuration.


A Conn is a fully configured half or full duplex communication channel that is point-to-point, only between two devices. It is ready to use like any readable and/or writable pipe.


Most connection-type specific subpackages include subpackages:

→ XXXreg: registry as that is populated by the host drivers and that can be leveraged by applications.

→ XXXtest: fake implementation that can be leveraged when writing device driver unit test.


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

// Using SPI as an example. See package ./spi/spireg for more details.
p, err := spireg.Open("")
if err != nil {
defer p.Close()
c, err := p.Connect(physic.MegaHertz, spi.Mode3, 8)
if err != nil {

// Write 0x10 to the device, and read a byte right after.
write := []byte{0x10, 0x00}
read := make([]byte, len(write))
if err := c.Tx(write, read); err != nil {
// Use read.
fmt.Printf("%v\n", read[1:])



Package Files

conn.go doc.go duplex_string.go

type Conn Uses

type Conn interface {
    String() string
    // Tx does a single transaction.
    // For full duplex protocols (generally SPI, UART), the two buffers must have
    // the same length as both reading and writing happen simultaneously.
    // For half duplex protocols (I²C), there is no restriction as reading
    // happens after writing, and r can be nil.
    // Query Limits.MaxTxSize() to know if there is a limit on the buffer size
    // per Tx() call.
    Tx(w, r []byte) error
    // Duplex returns the current duplex setting for this point-to-point
    // connection.
    // It is expected to be either Half or Full unless the connection itself is
    // in an unknown state.
    Duplex() Duplex

Conn defines the interface for a connection on a point-to-point communication channel.

The connection can either be unidirectional (read-only, write-only) or bidirectional (read-write). It can either be half-duplex or full duplex.

This is the lowest common denominator for all point-to-point communication channels.

Implementation are expected but not required to also implement the following interfaces:

- fmt.Stringer which returns something meaningful to the user like "SPI0.1", "I2C1.76", "COM6", etc.

- io.Reader and io.Writer as a way to use io.Copy() for half duplex operation.

- io.Closer for the owner of the communication channel.

type Duplex Uses

type Duplex int

Duplex declares whether communication can happen simultaneously both ways.

Some protocol can be either depending on configuration settings, like UART.

const (
    // DuplexUnknown is used when the duplex of a connection is yet to be known.
    // Some protocol can be configured either as half-duplex or full-duplex and
    // the connection is not yet is a determinate state.
    DuplexUnknown Duplex = 0
    // Half means that communication can only occurs one way at a time.
    // Examples include 1-wire and I²C.
    Half Duplex = 1
    // Full means that communication occurs simultaneously both ways in a
    // synchronized manner.
    // Examples include SPI (except 3-wire variant).
    Full Duplex = 2

func (Duplex) String Uses

func (i Duplex) String() string

type Limits Uses

type Limits interface {
    // MaxTxSize returns the maximum allowed data size to be sent as a single
    // I/O.
    // Returns 0 if undefined.
    MaxTxSize() int

Limits returns information about the connection's limits.

type Resource Uses

type Resource interface {
    // String returns a human readable identifier representing this resource in a
    // descriptive way for the user. It is the same signature as fmt.Stringer.
    String() string
    // Halt stops the resource.
    // Unlike a Conn, a Resource may not be closable, On the other hand, a
    // resource can be halted. What halting entails depends on the resource
    // device but it should stop motion, sensing loop, light emission or PWM
    // output and go back into an inert state.
    Halt() error

Resource is a basic resource (like a gpio pin) or a device.


conntestPackage conntest implements fakes for package conn.
displayPackage display implements interfaces for visual output devices.
display/displaytestPackage displaytest contains non-hardware devices implementations for testing or emulation purpose.
gpioPackage gpio defines digital pins.
gpio/gpioregPackage gpioreg defines a registry for the known digital pins.
gpio/gpiostreamPackage gpiostream defines digital streams.
gpio/gpiostream/gpiostreamtestPackage gpiostreamtest enables testing device driver using gpiostream.PinIn or PinOut.
gpio/gpiotestPackage gpiotest is meant to be used to test drivers using fake Pins.
i2cPackage i2c defines the API to communicate with devices over the I²C protocol.
i2c/i2cregPackage i2creg defines I²C bus registry to list buses present on the host.
i2c/i2ctestPackage i2ctest is meant to be used to test drivers over a fake I²C bus.
i2sPackage i2s will eventually define the API to communicate with devices over the I²S protocol.
irPackage ir defines InfraRed codes for use with a IR remote control.
jtagPackage jtag will eventually define the API to communicate with devices over the JTAG protocol.
mmrPackage mmr defines helpers to interact with devices exposing Memory Mapped Registers protocol.
onewirePackage onewire defines the API to communicate with devices over the Dallas Semiconductor / Maxim Integrated 1-wire protocol.
onewire/onewireregPackage onewirereg defines a registry for onewire buses present on the host.
onewire/onewiretestPackage onewiretest is meant to be used to test drivers over a fake 1-wire bus.
physicPackage physic declares types for physical input, outputs and measurement units.
pinPackage pin declare well known pins.
pin/pinregPackage pinreg is a registry for the physical headers (made up of pins) on a host.
spiPackage spi defines the API to communicate with devices over the SPI protocol.
spi/spiregPackage spireg defines the SPI registry for SPI ports discovered on the host.
spi/spitestPackage spitest is meant to be used to test drivers over a fake SPI port.
uartPackage uart will eventually define the API to communicate with devices over the UART protocol.

Package conn imports 1 packages (graph) and is imported by 77 packages. Updated 2019-08-06. Refresh now. Tools for package owners.