cap1188: tweaks in the device driver (#244)

- Change DefaultOpts to be a struct instead of a function. This makes the godoc
  much more descriptive.
- Change InputStatus() to accept a slice, so that the driver will be able to
  eventually support the flavors cap1155 and cap1166.

experimental/devices/cap1188/cap1188.go

@@ -17,6 +17,7 @@ import (
 	"encoding/binary"
 	"fmt"
 	"log"
+	"strconv"
 	"time"
 
 	"periph.io/x/periph/conn"
@@ -47,7 +48,7 @@ var touchStatusIndex = [...]uint8{0, 9, 22, 32, 46}
 
 func (i TouchStatus) String() string {
 	if i < 0 || i >= TouchStatus(len(touchStatusIndex)-1) {
-		return fmt.Sprintf("TouchStatus(%d)", i)
+		return "TouchStatus(" + strconv.Itoa(int(i)) + ")"
 	}
 	return touchStatusName[touchStatusIndex[i]:touchStatusIndex[i+1]]
 }
@@ -57,7 +58,7 @@ func (i TouchStatus) String() string {
 // Use default options if nil is used.
 func NewI2C(b i2c.Bus, opts *Opts) (*Dev, error) {
 	if opts == nil {
-		opts = DefaultOpts()
+		opts = &DefaultOpts
 	}
 	addr, err := opts.i2cAddr()
 	if err != nil {
@@ -100,13 +101,17 @@ func (d *Dev) Halt() error {
 	return nil
 }
 
-// InputStatus reads and returns the status of the 8 inputs.
+// InputStatus reads and returns the status of the inputs.
-func (d *Dev) InputStatus() ([8]TouchStatus, error) {
+//
+// The slice t will have the sensed inputs updated upon successful read. If the
+// slice is too long, extraneous elements are ignored. If the slice is too
+// short, only the provided subset is updated without error.
+func (d *Dev) InputStatus(t []TouchStatus) error {
 	d.resetSinceAtLeast(200 * time.Millisecond)
 	// Read inputs.
 	status, err := d.c.ReadUint8(0x3)
 	if err != nil {
-		return d.inputStatuses, wrapf("failed to read the input values: %v", err)
+		return wrapf("failed to read the input values: %v", err)
 	}
 
 	// Read deltas (in two's complement, capped at -128 to 127).
@@ -143,8 +148,8 @@ func (d *Dev) InputStatus() ([8]TouchStatus, error) {
 			d.inputStatuses[i] = OffStatus
 		}
 	}
-
+	copy(t, d.inputStatuses[:])
-	return d.inputStatuses, nil
+	return nil
 }
 
 // LinkLEDs links the behavior of the LEDs to the touch sensors.

experimental/devices/cap1188/cap1188_options.go

@@ -13,7 +13,6 @@ import (
 // SamplingTime determines the time to make a single sample.
 type SamplingTime uint8
 
-// Possible sampling time values. (written as 2 bits)
 const (
 	S320us SamplingTime = 0
 	S640us SamplingTime = 1
@@ -25,7 +24,6 @@ const (
 // AvgSampling set the number of samples per measurement that get averaged.
 type AvgSampling uint8
 
-// Possible average sampling values. (written as 3 bits)
 const (
 	// Avg1 means that 1 sample is taken per measurement
 	Avg1   AvgSampling = iota // 0
@@ -142,16 +140,14 @@ func (o *Opts) i2cAddr() (uint16, error) {
 	}
 }
 
-// DefaultOpts returns a pointer to a new Opts with the default option values.
+// DefaultOpts contains default options to use.
-func DefaultOpts() *Opts {
+var DefaultOpts = Opts{
-	return &Opts{
+	LinkedLEDs:            true,
-		LinkedLEDs:            true,
+	MaxTouchDuration:      MaxDur5600ms,
-		MaxTouchDuration:      MaxDur5600ms,
+	RetriggerOnHold:       false,
-		RetriggerOnHold:       false,
+	EnableRecalibration:   false,
-		EnableRecalibration:   false,
+	InterruptOnRelease:    false,
-		InterruptOnRelease:    false,
+	SamplesPerMeasurement: Avg1,
-		SamplesPerMeasurement: Avg1,
+	SamplingTime:          S1_28ms,
-		SamplingTime:          S1_28ms,
+	CycleTime:             C35ms,
-		CycleTime:             C35ms,
-	}
 }

experimental/devices/cap1188/cap1188_test.go

@@ -141,12 +141,12 @@ func TestDev_InputStatus(t *testing.T) {
 	}
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
-			d, err := NewI2C(tt.bus, DefaultOpts())
+			d, err := NewI2C(tt.bus, &DefaultOpts)
 			if err != nil {
 				t.Fatal(err)
 			}
-			got, err := d.InputStatus()
+			var got [8]TouchStatus
-			if err != nil {
+			if err := d.InputStatus(got[:]); err != nil {
 				t.Fatalf("Dev.InputStatus() error = %v", err)
 			}
 			if !reflect.DeepEqual(got, tt.want) {
@@ -173,24 +173,23 @@ func TestDev_InputStatus(t *testing.T) {
 		}
 		// Set the recorded response to have the retrigger option on.
 		bus.Ops[10] = i2ctest.IO{Addr: 40, W: []byte{0x28, 0xff}, R: nil}
-		opts := DefaultOpts()
+		opts := DefaultOpts
 		// Following option needs to be true so we can get the held status.
 		opts.RetriggerOnHold = true
-		d, err := NewI2C(bus, opts)
+		d, err := NewI2C(bus, &opts)
 		if err != nil {
 			t.Fatal(err)
 		}
 		// first check
-		got, err := d.InputStatus()
+		var got [8]TouchStatus
-		if err != nil {
+		if err := d.InputStatus(got[:]); err != nil {
 			t.Fatal(err)
 		}
 		if !reflect.DeepEqual(got, [8]TouchStatus{PressedStatus, OffStatus, OffStatus, OffStatus, OffStatus, OffStatus, OffStatus, OffStatus}) {
 			t.Fatalf("expected to have the first sensor touched but instead got %v", got)
 		}
 		// 2nd check
-		got, err = d.InputStatus()
+		if err = d.InputStatus(got[:]); err != nil {
-		if err != nil {
 			t.Fatal(err)
 		}
 		if !reflect.DeepEqual(got, [8]TouchStatus{HeldStatus, OffStatus, OffStatus, OffStatus, OffStatus, OffStatus, OffStatus, OffStatus}) {

experimental/devices/cap1188/example_test.go

@@ -42,12 +42,12 @@ func Example() {
 
 	// We will configure the cap1188 by setting some options, we can start by the
 	// defaults.
-	opts := cap1188.DefaultOpts()
+	opts := cap1188.DefaultOpts
 	opts.AlertPin = alertPin
 	opts.ResetPin = resetPin
 
 	// Open the device so we can detect touch events.
-	dev, err := cap1188.NewI2C(i2cBus, opts)
+	dev, err := cap1188.NewI2C(i2cBus, &opts)
 	if err != nil {
 		log.Fatalf("couldn't open cap1188: %v", err)
 	}
@@ -57,8 +57,8 @@ func Example() {
 	for maxTouches > 0 {
 		if alertPin.WaitForEdge(-1) {
 			maxTouches--
-			statuses, err := dev.InputStatus()
+			var statuses [8]cap1188.TouchStatus
-			if err != nil {
+			if err := dev.InputStatus(statuses[:]); err != nil {
 				fmt.Printf("Error reading inputs: %v\n", err)
 				continue
 			}