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// Copyright 2016 The Periph Authors. All rights reserved.
// Use of this source code is governed under the Apache License, Version 2.0
// that can be found in the LICENSE file.
package conn
import "strconv"
// Resource is a basic resource (like a gpio pin) or a device.
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
// Duplex declares whether communication can happen simultaneously both ways.
// Some protocol can be either depending on configuration settings, like UART.
type Duplex int
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
const duplexName = "DuplexUnknownHalfFull"
var duplexIndex = [...]uint8{0, 13, 17, 21}
func (i Duplex) String() string {
if i < 0 || i >= Duplex(len(duplexIndex)-1) {
return "Duplex(" + strconv.Itoa(int(i)) + ")"
return duplexName[duplexIndex[i]:duplexIndex[i+1]]
// 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 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
// Limits returns information about the connection's limits.
type Limits interface {
// MaxTxSize returns the maximum allowed data size to be sent as a single
// I/O.
// Returns 0 if undefined.
MaxTxSize() int
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