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digital_interrupts.go
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digital_interrupts.go
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package board
import (
"context"
"sync"
"sync/atomic"
"github.com/erh/scheme"
"github.com/pkg/errors"
"go.viam.com/rdk/utils"
)
// ServoRollingAverageWindow is how many entries to average over for
// servo ticks.
const ServoRollingAverageWindow = 10
// Tick represents a signal received by an interrupt pin. This signal is communicated
// via registered channel to the various drivers. Depending on board implementation there may be a
// wraparound in timestamp values past 4294967295000 nanoseconds (~72 minutes) if the value
// was originally in microseconds as a 32-bit integer. The timestamp in nanoseconds of the
// tick SHOULD ONLY BE USED FOR CALCULATING THE TIME ELAPSED BETWEEN CONSECUTIVE TICKS AND NOT
// AS AN ABSOLUTE TIMESTAMP.
type Tick struct {
High bool
TimestampNanosec uint64
}
// A DigitalInterrupt represents a configured interrupt on the board that
// when interrupted, calls the added callbacks. Post processors can also
// be added to modify what Value ultimately returns.
type DigitalInterrupt interface {
// Value returns the current value of the interrupt which is
// based on the type of interrupt.
Value(ctx context.Context, extra map[string]interface{}) (int64, error)
// Tick is to be called either manually if the interrupt is a proxy to some real
// hardware interrupt or for tests.
// nanoseconds is from an arbitrary point in time, but always increasing and always needs
// to be accurate.
Tick(ctx context.Context, high bool, nanoseconds uint64) error
// AddCallback adds a callback to be sent a low/high value to when a tick
// happens.
AddCallback(c chan Tick)
// AddPostProcessor adds a post processor that should be used to modify
// what is returned by Value.
AddPostProcessor(pp PostProcessor)
// RemoveCallback removes a listener for interrupts
RemoveCallback(c chan Tick)
Close(ctx context.Context) error
}
// A ReconfigurableDigitalInterrupt is a simple reconfigurable digital interrupt that expects
// reconfiguration within the same type.
type ReconfigurableDigitalInterrupt interface {
DigitalInterrupt
Reconfigure(cfg DigitalInterruptConfig) error
}
// CreateDigitalInterrupt is a factory method for creating a specific DigitalInterrupt based
// on the given config. If no type is specified, a BasicDigitalInterrupt is returned.
func CreateDigitalInterrupt(cfg DigitalInterruptConfig) (DigitalInterrupt, error) {
if cfg.Type == "" {
cfg.Type = "basic"
}
var i ReconfigurableDigitalInterrupt
switch cfg.Type {
case "basic":
i = &BasicDigitalInterrupt{}
case "servo":
i = &ServoDigitalInterrupt{ra: utils.NewRollingAverage(ServoRollingAverageWindow)}
default:
panic(errors.Errorf("unknown interrupt type (%s)", cfg.Type))
}
if err := i.Reconfigure(cfg); err != nil {
return nil, err
}
return i, nil
}
// A BasicDigitalInterrupt records how many ticks/interrupts happen and can
// report when they happen to interested callbacks.
type BasicDigitalInterrupt struct {
count int64
callbacks []chan Tick
mu sync.RWMutex
cfg DigitalInterruptConfig
pp PostProcessor
}
// Config returns the config used to create this interrupt.
func (i *BasicDigitalInterrupt) Config(ctx context.Context) (DigitalInterruptConfig, error) {
i.mu.RLock()
defer i.mu.RUnlock()
return i.cfg, nil
}
// Value returns the amount of ticks that have occurred.
func (i *BasicDigitalInterrupt) Value(ctx context.Context, extra map[string]interface{}) (int64, error) {
i.mu.RLock()
defer i.mu.RUnlock()
count := atomic.LoadInt64(&i.count)
if i.pp != nil {
return i.pp(count), nil
}
return count, nil
}
// Ticks is really just for testing.
func (i *BasicDigitalInterrupt) Ticks(ctx context.Context, num int, now uint64) error {
for x := 0; x < num; x++ {
if err := i.Tick(ctx, true, now+uint64(x)); err != nil {
return err
}
}
return nil
}
// Tick records an interrupt and notifies any interested callbacks. See comment on
// the DigitalInterrupt interface for caveats.
func (i *BasicDigitalInterrupt) Tick(ctx context.Context, high bool, nanoseconds uint64) error {
if high {
atomic.AddInt64(&i.count, 1)
}
i.mu.RLock()
defer i.mu.RUnlock()
for _, c := range i.callbacks {
select {
case <-ctx.Done():
return errors.New("context cancelled")
case c <- Tick{High: high, TimestampNanosec: nanoseconds}:
}
}
return nil
}
// AddCallback adds a listener for interrupts.
func (i *BasicDigitalInterrupt) AddCallback(c chan Tick) {
i.mu.Lock()
defer i.mu.Unlock()
i.callbacks = append(i.callbacks, c)
}
// RemoveCallback removes a listener for interrupts.
func (i *BasicDigitalInterrupt) RemoveCallback(c chan Tick) {
i.mu.Lock()
defer i.mu.Unlock()
for id := range i.callbacks {
if i.callbacks[id] == c {
// To remove this item, we replace it with the last item in the list, then truncate the
// list by 1.
i.callbacks[id] = i.callbacks[len(i.callbacks)-1]
i.callbacks = i.callbacks[:len(i.callbacks)-1]
break
}
}
}
// AddPostProcessor sets the post processor that will modify the value that
// Value returns.
func (i *BasicDigitalInterrupt) AddPostProcessor(pp PostProcessor) {
i.mu.Lock()
defer i.mu.Unlock()
i.pp = pp
}
// Close does nothing.
func (i *BasicDigitalInterrupt) Close(ctx context.Context) error {
return nil
}
func processFormula(oldFormula, newFormula, name string) (func(raw int64) int64, bool, error) {
if oldFormula == newFormula {
return nil, false, nil
}
x, err := scheme.Parse(newFormula)
if err != nil {
return nil, false, errors.Wrapf(err, "couldn't parse formula for %s", name)
}
testScope := scheme.Scope{}
num := 1.0
testScope["raw"] = &scheme.Value{Float: &num}
_, err = scheme.Eval(x, testScope)
if err != nil {
return nil, false, errors.Wrapf(err, "test exec failed for %s", name)
}
return func(raw int64) int64 {
scope := scheme.Scope{}
rr := float64(raw) // TODO(erh): fix
scope["raw"] = &scheme.Value{Float: &rr}
res, err := scheme.Eval(x, scope)
if err != nil {
panic(err)
}
f, err := res.ToFloat()
if err != nil {
panic(err)
}
return int64(f)
}, true, nil
}
// Reconfigure reconfigures this digital interrupt with a new formula.
func (i *BasicDigitalInterrupt) Reconfigure(conf DigitalInterruptConfig) error {
i.mu.Lock()
defer i.mu.Unlock()
newFormula, isNew, err := processFormula(i.cfg.Formula, conf.Formula, conf.Name)
if err != nil {
return err
}
if !isNew {
return nil
}
i.pp = newFormula
i.cfg = conf
return nil
}
// A ServoDigitalInterrupt is an interrupt associated with a servo in order to
// track the amount of time that has passed between low signals (pulse width). Post processors
// make meaning of these widths.
type ServoDigitalInterrupt struct {
last uint64
ra *utils.RollingAverage
mu sync.RWMutex
cfg DigitalInterruptConfig
pp PostProcessor
}
// Config returns the config the interrupt was created with.
func (i *ServoDigitalInterrupt) Config(ctx context.Context) (DigitalInterruptConfig, error) {
i.mu.RLock()
defer i.mu.RUnlock()
return i.cfg, nil
}
// Value will return the window averaged value followed by its post processed
// result.
func (i *ServoDigitalInterrupt) Value(ctx context.Context, extra map[string]interface{}) (int64, error) {
i.mu.RLock()
defer i.mu.RUnlock()
v := int64(i.ra.Average())
if i.pp != nil {
return i.pp(v), nil
}
return v, nil
}
// Tick records the time between two successive low signals (pulse width). How it is
// interpreted is based off the consumer of Value.
func (i *ServoDigitalInterrupt) Tick(ctx context.Context, high bool, now uint64) error {
i.mu.RLock()
defer i.mu.RUnlock()
diff := now - i.last
i.last = now
if i.last == 0 {
return nil
}
if high {
// this is time between signals, ignore
return nil
}
i.ra.Add(int(diff / 1000))
return nil
}
// AddCallback currently panics.
func (i *ServoDigitalInterrupt) AddCallback(c chan Tick) {
i.mu.Lock()
defer i.mu.Unlock()
panic("servos can't have callback")
}
// RemoveCallback currently panics.
func (i *ServoDigitalInterrupt) RemoveCallback(c chan Tick) {
i.mu.Lock()
defer i.mu.Unlock()
panic("servos can't have callback")
}
// AddPostProcessor sets the post processor that will modify the value that
// Value returns.
func (i *ServoDigitalInterrupt) AddPostProcessor(pp PostProcessor) {
i.mu.Lock()
defer i.mu.Unlock()
i.pp = pp
}
// Reconfigure reconfigures this digital interrupt with a new formula.
func (i *ServoDigitalInterrupt) Reconfigure(conf DigitalInterruptConfig) error {
i.mu.Lock()
defer i.mu.Unlock()
newFormula, isNew, err := processFormula(i.cfg.Formula, conf.Formula, conf.Name)
if err != nil {
return err
}
if !isNew {
return nil
}
i.pp = newFormula
i.cfg = conf
return nil
}
// Close does nothing.
func (i *ServoDigitalInterrupt) Close(ctx context.Context) error {
return nil
}