hx711: implement pin.PinFunc

The interface pin.PinFunc will be merged into pin.Pin in v4.

Increase coverage to 84%.

experimental/devices/hx711/hx711.go

@@ -16,6 +16,7 @@ import (
 	"time"
 
 	"periph.io/x/periph/conn/gpio"
+	"periph.io/x/periph/conn/pin"
 	"periph.io/x/periph/experimental/conn/analog"
 )
 
@@ -87,7 +88,25 @@ func (d *Dev) Number() int {
 
 // Function implements analog.PinADC.
 func (d *Dev) Function() string {
-	return "ADC"
+	return string(d.Func())
+}
+
+// Func implements analog.PinADC.
+func (d *Dev) Func() pin.Func {
+	return analog.ADC
+}
+
+// SupportedFuncs implements analog.PinADC.
+func (d *Dev) SupportedFuncs() []pin.Func {
+	return []pin.Func{analog.ADC}
+}
+
+// SetFunc implements analog.PinADC.
+func (d *Dev) SetFunc(f pin.Func) error {
+	if f == analog.ADC {
+		return nil
+	}
+	return errors.New("pin function cannot be changed")
 }
 
 // SetInputMode changes the voltage gain and channel multiplexer mode.

experimental/devices/hx711/hx711_test.go

@@ -6,11 +6,14 @@ package hx711
 
 import (
 	"errors"
+	"reflect"
 	"testing"
 	"time"
 
 	"periph.io/x/periph/conn/gpio"
 	"periph.io/x/periph/conn/gpio/gpiotest"
+	"periph.io/x/periph/conn/pin"
+	"periph.io/x/periph/experimental/conn/analog"
 )
 
 func TestNew(t *testing.T) {
@@ -32,6 +35,18 @@ func TestNew(t *testing.T) {
 	if f := d.Function(); f != "ADC" {
 		t.Fatal(f)
 	}
+	if f := d.Func(); f != analog.ADC {
+		t.Fatal(f)
+	}
+	if v := d.SupportedFuncs(); !reflect.DeepEqual(v, []pin.Func{analog.ADC}) {
+		t.Fatal(v)
+	}
+	if err := d.SetFunc(analog.ADC); err != nil {
+		t.Fatal(err)
+	}
+	if err := d.SetFunc(pin.FuncNone); err == nil {
+		t.Fatal("expected failure")
+	}
 	min, max := d.Range()
 	// TODO(davidsansome): Is that the right values?
 	if min.Raw != -8388608 {