hx711: implement analog.PinADC (#335)

Add locking.
Add minimal testing.

experimental/devices/hx711/hx711.go

@@ -2,7 +2,8 @@
 // Use of this source code is governed under the Apache License, Version 2.0
 // that can be found in the LICENSE file.
 
-// Package hx711 implements an interface to the HX711 analog to digital converter.
+// Package hx711 implements an interface to the 24-bits HX711 analog to digital
+// converter.
 //
 // Datasheet
 //
@@ -11,9 +12,11 @@ package hx711
 
 import (
 	"errors"
+	"sync"
 	"time"
 
 	"periph.io/x/periph/conn/gpio"
+	"periph.io/x/periph/experimental/conn/analog"
 )
 
 var (
@@ -33,27 +36,32 @@ const (
 	CHANNEL_B_GAIN_32  InputMode = 2
 )
 
+// Dev is a handle to a hx711.
 type Dev struct {
+	// Immutable.
+	name string
+	clk  gpio.PinOut
+	data gpio.PinIn
+
+	// Mutable.
+	mu        sync.Mutex
 	inputMode InputMode
-	clk       gpio.PinOut
-	data      gpio.PinIn
 	done      chan struct{}
 }
 
 // New creates a new HX711 device.
-// The data pin must support edge detection.  If your pin doesn't natively
-// support edge detection you can use PollEdge from
-// periph.io/x/periph/experimental/conn/gpio/gpioutil
+//
+// The data pin must support edge detection. If your pin doesn't natively
+// support edge detection you can use PollEdge from gpioutil.
 func New(clk gpio.PinOut, data gpio.PinIn) (*Dev, error) {
 	if err := data.In(gpio.PullDown, gpio.FallingEdge); err != nil {
 		return nil, err
 	}
-
 	if err := clk.Out(gpio.Low); err != nil {
 		return nil, err
 	}
-
 	return &Dev{
+		name:      "hx711{" + clk.Name() + ", " + data.Name() + "}",
 		inputMode: CHANNEL_A_GAIN_128,
 		clk:       clk,
 		data:      data,
@@ -61,68 +69,63 @@ func New(clk gpio.PinOut, data gpio.PinIn) (*Dev, error) {
 	}, nil
 }
 
-// SetInputMode changes the voltage gain and channel multiplexer mode.
-func (d *Dev) SetInputMode(inputMode InputMode) {
-	d.inputMode = inputMode
-	d.readImmediately()
+// String implements analog.PinADC.
+func (d *Dev) String() string {
+	return d.name
 }
 
-// IsReady returns true if there is data ready to be read from the ADC.
-func (d *Dev) IsReady() bool {
-	return d.data.Read() == gpio.Low
+// Name implements analog.PinADC.
+func (d *Dev) Name() string {
+	return d.String()
 }
 
-// Read reads a single value from the ADC.  It blocks until the ADC indicates
-// there is data ready for retrieval.  If the ADC doesn't pull its Data pin low
-// to indicate there is data ready before the timeout is reached, TimeoutError
-// is returned.
-func (d *Dev) Read(timeout time.Duration) (int32, error) {
-	// Wait for the falling edge that indicates the ADC has data.
-	if !d.IsReady() {
-		if !d.data.WaitForEdge(timeout) {
-			return 0, TimeoutError
-		}
-	}
+// Number implements analog.PinADC.
+func (d *Dev) Number() int {
+	return -1
+}
 
-	return d.readImmediately(), nil
+// Function implements analog.PinADC.
+func (d *Dev) Function() string {
+	return "ADC"
 }
 
-func (d *Dev) readImmediately() int32 {
-	// Shift the 24-bit 2's compliment value.
-	var value uint32
-	for i := 0; i < 24; i++ {
-		d.clk.Out(gpio.High)
-		level := d.data.Read()
-		d.clk.Out(gpio.Low)
+// SetInputMode changes the voltage gain and channel multiplexer mode.
+func (d *Dev) SetInputMode(inputMode InputMode) error {
+	d.mu.Lock()
+	defer d.mu.Unlock()
+	d.inputMode = inputMode
+	_, err := d.readRaw()
+	return err
+}
 
-		value <<= 1
-		if level {
-			value |= 1
-		}
-	}
+// Range implements analog.PinADC.
+func (d *Dev) Range() (analog.Sample, analog.Sample) {
+	return analog.Sample{Raw: -(1 << 23)}, analog.Sample{Raw: 1 << 23}
+}
 
-	// Pulse the clock 1-3 more times to set the new ADC mode.
-	for i := 0; i < int(d.inputMode); i++ {
-		d.clk.Out(gpio.High)
-		d.clk.Out(gpio.Low)
-	}
-	// Convert the 24-bit 2's compliment value to a 32-bit signed value.
-	return int32(value<<8) >> 8
+// Read implements analog.PinADC.
+func (d *Dev) Read() (analog.Sample, error) {
+	d.mu.Lock()
+	defer d.mu.Unlock()
+	raw, err := d.readRaw()
+	return analog.Sample{Raw: raw}, err
 }
 
-// StartContinuousRead starts reading values continuously from the ADC.  It
+// ReadContinuous starts reading values continuously from the ADC. It
 // returns a channel that you can use to receive these values.
 //
 // You must call Halt to stop reading.
 //
-// Calling StartContinuousRead again before Halt is an error,
+// Calling ReadContinuous again before Halt is an error,
 // and nil will be returned.
-func (d *Dev) StartContinuousRead() <-chan int32 {
+func (d *Dev) ReadContinuous() <-chan analog.Sample {
+	d.mu.Lock()
+	defer d.mu.Unlock()
 	if d.done != nil {
 		return nil
 	}
 	done := make(chan struct{})
-	ret := make(chan int32)
+	ret := make(chan analog.Sample)
 
 	go func() {
 		for {
@@ -131,9 +134,9 @@ func (d *Dev) StartContinuousRead() <-chan int32 {
 				close(ret)
 				return
 			default:
-				value, err := d.Read(time.Second)
+				value, err := d.ReadTimeout(time.Second)
 				if err == nil {
-					ret <- value
+					ret <- analog.Sample{Raw: value}
 				}
 			}
 		}
@@ -143,11 +146,70 @@ func (d *Dev) StartContinuousRead() <-chan int32 {
 	return ret
 }
 
-// Halt stops a continuous read that was started with StartContinuousRead.
-// This will close the channel that was returned by StartContinuousRead.
-func (d *Dev) Halt() {
+// Halt stops a continuous read that was started with ReadContinuous.
+//
+// This will close the channel that was returned by ReadContinuous.
+func (d *Dev) Halt() error {
+	d.mu.Lock()
+	defer d.mu.Unlock()
 	if d.done != nil {
 		close(d.done)
 		d.done = nil
 	}
+	return nil
+}
+
+// IsReady returns true if there is data ready to be read from the ADC.
+func (d *Dev) IsReady() bool {
+	return d.data.Read() == gpio.Low
+}
+
+// ReadTimeout reads a single value from the ADC.
+//
+// It blocks until the ADC indicates there is data ready for retrieval. If the
+// ADC doesn't pull its Data pin low to indicate there is data ready before the
+// timeout is reached, TimeoutError is returned.
+func (d *Dev) ReadTimeout(timeout time.Duration) (int32, error) {
+	// Wait for the falling edge that indicates the ADC has data.
+	d.mu.Lock()
+	defer d.mu.Unlock()
+	if !d.IsReady() {
+		if !d.data.WaitForEdge(timeout) {
+			return 0, TimeoutError
+		}
+	}
+	return d.readRaw()
 }
+
+func (d *Dev) readRaw() (int32, error) {
+	// Shift the 24-bit 2's compliment value.
+	var value uint32
+	for i := 0; i < 24; i++ {
+		if err := d.clk.Out(gpio.High); err != nil {
+			return 0, err
+		}
+		level := d.data.Read()
+		if err := d.clk.Out(gpio.Low); err != nil {
+			return 0, err
+		}
+
+		value <<= 1
+		if level {
+			value |= 1
+		}
+	}
+
+	// Pulse the clock 1-3 more times to set the new ADC mode.
+	for i := 0; i < int(d.inputMode); i++ {
+		if err := d.clk.Out(gpio.High); err != nil {
+			return 0, err
+		}
+		if err := d.clk.Out(gpio.Low); err != nil {
+			return 0, err
+		}
+	}
+	// Convert the 24-bit 2's compliment value to a 32-bit signed value.
+	return int32(value<<8) >> 8, nil
+}
+
+var _ analog.PinADC = &Dev{}

experimental/devices/hx711/hx711_test.go

@@ -0,0 +1,128 @@
+// Copyright 2018 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 hx711
+
+import (
+	"errors"
+	"testing"
+	"time"
+
+	"periph.io/x/periph/conn/gpio"
+	"periph.io/x/periph/conn/gpio/gpiotest"
+)
+
+func TestNew(t *testing.T) {
+	clk := gpiotest.Pin{N: "clk"}
+	data := gpiotest.Pin{N: "data", EdgesChan: make(chan gpio.Level)}
+	d, err := New(&clk, &data)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if s := d.String(); s != "hx711{clk, data}" {
+		t.Fatal(s)
+	}
+	if s := d.Name(); s != "hx711{clk, data}" {
+		t.Fatal(s)
+	}
+	if n := d.Number(); n != -1 {
+		t.Fatal(n)
+	}
+	if f := d.Function(); f != "ADC" {
+		t.Fatal(f)
+	}
+	min, max := d.Range()
+	// TODO(davidsansome): Is that the right values?
+	if min.Raw != -8388608 {
+		t.Fatal(min.Raw)
+	}
+	if max.Raw != 8388608 {
+		t.Fatal(max.Raw)
+	}
+	if !d.IsReady() {
+		t.Fatal("data is low")
+	}
+	if err := d.SetInputMode(CHANNEL_A_GAIN_128); err != nil {
+		t.Fatal(err)
+	}
+	if err := d.Halt(); err != nil {
+		t.Fatal(err)
+	}
+}
+
+func TestNew_Fail(t *testing.T) {
+	ok := gpiotest.Pin{N: "ok", EdgesChan: make(chan gpio.Level)}
+	fail := failPin{gpiotest.Pin{N: "fail"}}
+	if _, err := New(&fail, &ok); err == nil {
+		t.Fatal("expected failure")
+	}
+	if _, err := New(&ok, &fail); err == nil {
+		t.Fatal("expected failure")
+	}
+}
+
+func TestRead(t *testing.T) {
+	clk := gpiotest.Pin{N: "clk"}
+	data := gpiotest.Pin{N: "data", EdgesChan: make(chan gpio.Level)}
+	d, err := New(&clk, &data)
+	if err != nil {
+		t.Fatal(err)
+	}
+	// TODO(davidsansome): Real testing.
+	r, err := d.Read()
+	if err != nil {
+		t.Fatal(err)
+	}
+	if r.Raw != 0 {
+		t.Fatal("we should implement something")
+	}
+}
+
+func TestReadTimeout(t *testing.T) {
+	clk := gpiotest.Pin{N: "clk"}
+	data := gpiotest.Pin{N: "data", EdgesChan: make(chan gpio.Level)}
+	d, err := New(&clk, &data)
+	if err != nil {
+		t.Fatal(err)
+	}
+	// TODO(davidsansome): Real testing.
+	r, err := d.ReadTimeout(time.Second)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if r != 0 {
+		t.Fatal("we should implement something")
+	}
+}
+
+func TestReadContinuous(t *testing.T) {
+	clk := gpiotest.Pin{N: "clk"}
+	data := gpiotest.Pin{N: "data", EdgesChan: make(chan gpio.Level)}
+	d, err := New(&clk, &data)
+	if err != nil {
+		t.Fatal(err)
+	}
+	// TODO(davidsansome): Real testing.
+	c := d.ReadContinuous()
+	if c == nil {
+		t.Fatal("expected chan")
+	}
+	if err := d.Halt(); err != nil {
+		t.Fatal(err)
+	}
+}
+
+//
+
+type failPin struct {
+	gpiotest.Pin
+}
+
+func (f *failPin) In(pull gpio.Pull, edge gpio.Edge) error {
+	return errors.New("fail")
+}
+
+func (f *failPin) Out(l gpio.Level) error {
+	return errors.New("fail")
+}