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incremental_encoder.go
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/
incremental_encoder.go
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// Package incremental implements an incremental encoder
package incremental
import (
"context"
"math"
"sync"
"sync/atomic"
"github.com/pkg/errors"
"go.uber.org/multierr"
"go.viam.com/utils"
"go.viam.com/rdk/components/board"
"go.viam.com/rdk/components/encoder"
"go.viam.com/rdk/logging"
"go.viam.com/rdk/resource"
)
var incrModel = resource.DefaultModelFamily.WithModel("incremental")
func init() {
resource.RegisterComponent(
encoder.API,
incrModel,
resource.Registration[encoder.Encoder, *Config]{
Constructor: NewIncrementalEncoder,
})
}
// Encoder keeps track of a motor position using a rotary incremental encoder.
type Encoder struct {
resource.Named
mu sync.Mutex
A, B board.DigitalInterrupt
// The position is pRaw with the least significant bit chopped off.
position int64
// pRaw is the number of half-ticks we've gone through: it increments or decrements whenever
// either pin on the encoder changes.
pRaw int64
// pState is the previous state: the least significant bit is the value of pin A, and the
// second-least-significant bit is pin B. It is used to determine whether to increment or
// decrement pRaw.
pState int64
boardName string
encAName string
encBName string
logger logging.Logger
cancelCtx context.Context
cancelFunc func()
activeBackgroundWorkers sync.WaitGroup
positionType encoder.PositionType
}
// Pins describes the configuration of Pins for a quadrature encoder.
type Pins struct {
A string `json:"a"`
B string `json:"b"`
}
// Config describes the configuration of a quadrature encoder.
type Config struct {
Pins Pins `json:"pins"`
BoardName string `json:"board"`
}
// Validate ensures all parts of the config are valid.
func (conf *Config) Validate(path string) ([]string, error) {
var deps []string
if conf.Pins.A == "" {
return nil, errors.New("expected nonempty string for a")
}
if conf.Pins.B == "" {
return nil, errors.New("expected nonempty string for b")
}
if len(conf.BoardName) == 0 {
return nil, errors.New("expected nonempty board")
}
deps = append(deps, conf.BoardName)
return deps, nil
}
// NewIncrementalEncoder creates a new Encoder.
func NewIncrementalEncoder(
ctx context.Context,
deps resource.Dependencies,
conf resource.Config,
logger logging.Logger,
) (encoder.Encoder, error) {
cancelCtx, cancelFunc := context.WithCancel(context.Background())
e := &Encoder{
Named: conf.ResourceName().AsNamed(),
logger: logger,
cancelCtx: cancelCtx,
cancelFunc: cancelFunc,
position: 0,
positionType: encoder.PositionTypeTicks,
pRaw: 0,
pState: 0,
}
if err := e.Reconfigure(ctx, deps, conf); err != nil {
return nil, err
}
return e, nil
}
// Reconfigure atomically reconfigures this encoder in place based on the new config.
func (e *Encoder) Reconfigure(
ctx context.Context,
deps resource.Dependencies,
conf resource.Config,
) error {
newConf, err := resource.NativeConfig[*Config](conf)
if err != nil {
return err
}
e.mu.Lock()
existingBoardName := e.boardName
existingEncAName := e.encAName
existingEncBName := e.encBName
e.mu.Unlock()
needRestart := existingBoardName != newConf.BoardName ||
existingEncAName != newConf.Pins.A ||
existingEncBName != newConf.Pins.B
board, err := board.FromDependencies(deps, newConf.BoardName)
if err != nil {
return err
}
encA, err := board.DigitalInterruptByName(newConf.Pins.A)
if err != nil {
return multierr.Combine(errors.Errorf("cannot find pin (%s) for incremental Encoder", newConf.Pins.A), err)
}
encB, err := board.DigitalInterruptByName(newConf.Pins.B)
if err != nil {
return multierr.Combine(errors.Errorf("cannot find pin (%s) for incremental Encoder", newConf.Pins.B), err)
}
if !needRestart {
return nil
}
utils.UncheckedError(e.Close(ctx))
cancelCtx, cancelFunc := context.WithCancel(context.Background())
e.cancelCtx = cancelCtx
e.cancelFunc = cancelFunc
e.mu.Lock()
e.A = encA
e.B = encB
e.boardName = newConf.BoardName
e.encAName = newConf.Pins.A
e.encBName = newConf.Pins.B
// state is not really valid anymore
atomic.StoreInt64(&e.position, 0)
atomic.StoreInt64(&e.pRaw, 0)
atomic.StoreInt64(&e.pState, 0)
e.mu.Unlock()
e.Start(ctx, board)
return nil
}
// Start starts the Encoder background thread.
func (e *Encoder) Start(ctx context.Context, b board.Board) {
/**
a rotary encoder looks like
picture from https://github.com/joan2937/pigpio/blob/master/EXAMPLES/C/ROTARY_ENCODER/rotary_encoder.c
1 2 3 4 1 2 3 4 1
+---------+ +---------+ 0
| | | |
A | | | |
| | | |
+---------+ +---------+ +----- 1
+---------+ +---------+ 0
| | | |
B | | | |
| | | |
----+ +---------+ +---------+ 1
*/
// State Transition Table
// +---------------+----+----+----+----+
// | pState/nState | 00 | 01 | 10 | 11 |
// +---------------+----+----+----+----+
// | 00 | 0 | -1 | +1 | x |
// +---------------+----+----+----+----+
// | 01 | +1 | 0 | x | -1 |
// +---------------+----+----+----+----+
// | 10 | -1 | x | 0 | +1 |
// +---------------+----+----+----+----+
// | 11 | x | +1 | -1 | 0 |
// +---------------+----+----+----+----+
// 0 -> same state
// x -> impossible state
ch := make(chan board.Tick)
err := b.StreamTicks(e.cancelCtx, []board.DigitalInterrupt{e.A, e.B}, ch, nil)
if err != nil {
utils.Logger.Errorw("error getting digital interrupt ticks", "error", err)
return
}
aLevel, err := e.A.Value(ctx, nil)
if err != nil {
utils.Logger.Errorw("error reading a level", "error", err)
}
bLevel, err := e.B.Value(ctx, nil)
if err != nil {
utils.Logger.Errorw("error reading b level", "error", err)
}
e.pState = aLevel | (bLevel << 1)
e.activeBackgroundWorkers.Add(1)
utils.ManagedGo(func() {
for {
// This looks redundant with the other select statement below, but it's not: if we're
// supposed to return, we need to do that even if chanA and chanB are full of data, and
// the other select statement will pick random cases in that situation. This select
// statement guarantees that we'll return if we're supposed to, regardless of whether
// there's data in the other channels.
select {
case <-e.cancelCtx.Done():
return
default:
}
var tick board.Tick
select {
case <-e.cancelCtx.Done():
return
case tick = <-ch:
if tick.Name == e.encAName {
aLevel = 0
if tick.High {
aLevel = 1
}
}
if tick.Name == e.encBName {
bLevel = 0
if tick.High {
bLevel = 1
}
}
}
nState := aLevel | (bLevel << 1)
if e.pState == nState {
continue
}
switch (e.pState << 2) | nState {
case 0b0001:
fallthrough
case 0b0111:
fallthrough
case 0b1000:
fallthrough
case 0b1110:
atomic.AddInt64(&e.pRaw, -1)
case 0b0010:
fallthrough
case 0b0100:
fallthrough
case 0b1011:
fallthrough
case 0b1101:
atomic.AddInt64(&e.pRaw, 1)
}
atomic.StoreInt64(&e.position, atomic.LoadInt64(&e.pRaw)>>1)
e.pState = nState
}
}, e.activeBackgroundWorkers.Done)
}
// Position returns the current position in terms of ticks or
// degrees, and whether it is a relative or absolute position.
func (e *Encoder) Position(
ctx context.Context,
positionType encoder.PositionType,
extra map[string]interface{},
) (float64, encoder.PositionType, error) {
if positionType == encoder.PositionTypeDegrees {
return math.NaN(), encoder.PositionTypeUnspecified, encoder.NewPositionTypeUnsupportedError(positionType)
}
res := atomic.LoadInt64(&e.position)
return float64(res), e.positionType, nil
}
// ResetPosition sets the current position of the motor (adjusted by a given offset)
// to be its new zero position.
func (e *Encoder) ResetPosition(ctx context.Context, extra map[string]interface{}) error {
atomic.StoreInt64(&e.position, 0)
atomic.StoreInt64(&e.pRaw, atomic.LoadInt64(&e.pRaw)&0x1)
return nil
}
// Properties returns a list of all the position types that are supported by a given encoder.
func (e *Encoder) Properties(ctx context.Context, extra map[string]interface{}) (encoder.Properties, error) {
return encoder.Properties{
TicksCountSupported: true,
AngleDegreesSupported: false,
}, nil
}
// RawPosition returns the raw position of the encoder.
func (e *Encoder) RawPosition() int64 {
return atomic.LoadInt64(&e.pRaw)
}
// Close shuts down the Encoder.
func (e *Encoder) Close(ctx context.Context) error {
e.logger.Info("closing encoder")
e.cancelFunc()
e.logger.Info("cancelled context")
e.activeBackgroundWorkers.Wait()
e.logger.Info("background workers done")
return nil
}