make the process of registered available hosts less clunky

describe.go

@@ -1,31 +0,0 @@
-package embd
-
-import (
-	"errors"
-
-	"github.com/kidoman/embd/gpio"
-	"github.com/kidoman/embd/host/bbb"
-	"github.com/kidoman/embd/host/rpi"
-	"github.com/kidoman/embd/i2c"
-)
-
-type descriptor interface {
-	GPIO() gpio.GPIO
-	I2C() i2c.I2C
-}
-
-func describeHost() (descriptor, error) {
-	host, rev, err := DetectHost()
-	if err != nil {
-		return nil, err
-	}
-
-	switch host {
-	case HostRPi:
-		return rpi.Descriptor(rev), nil
-	case HostBBB:
-		return bbb.Descriptor(rev), nil
-	default:
-		return nil, errors.New("host: invalid host")
-	}
-}

hal.go

@@ -2,6 +2,7 @@ package embd
 
 import (
 	"github.com/kidoman/embd/gpio"
+	"github.com/kidoman/embd/host"
 	"github.com/kidoman/embd/i2c"
 )
 
@@ -16,7 +17,7 @@ const (
 )
 
 func NewGPIO() (gpio.GPIO, error) {
-	desc, err := describeHost()
+	desc, err := host.Describe()
 	if err != nil {
 		return nil, err
 	}
@@ -25,7 +26,7 @@ func NewGPIO() (gpio.GPIO, error) {
 }
 
 func NewI2C() (i2c.I2C, error) {
-	desc, err := describeHost()
+	desc, err := host.Describe()
 	if err != nil {
 		return nil, err
 	}

host/bbb/descriptor.go

@@ -4,20 +4,18 @@ import (
 	lgpio "github.com/kidoman/embd/driver/linux/gpio"
 	li2c "github.com/kidoman/embd/driver/linux/i2c"
 	"github.com/kidoman/embd/gpio"
-	"github.com/kidoman/embd/i2c"
+	"github.com/kidoman/embd/host"
 )
 
-type descriptor struct {
+func init() {
+	host.Describers[host.BBB] = describer
 }
 
-func (d *descriptor) GPIO() gpio.GPIO {
-	return lgpio.New(pins)
-}
-
-func (d *descriptor) I2C() i2c.I2C {
-	return li2c.New()
-}
-
-func Descriptor(rev int) *descriptor {
-	return &descriptor{}
+func describer(rev int) *host.Descriptor {
+	return &host.Descriptor{
+		GPIO: func() gpio.GPIO {
+			return lgpio.New(pins)
+		},
+		I2C: li2c.New,
+	}
 }

host/descriptor.go

@@ -0,0 +1,31 @@
+package host
+
+import (
+	"errors"
+
+	"github.com/kidoman/embd/gpio"
+	"github.com/kidoman/embd/i2c"
+)
+
+type Descriptor struct {
+	GPIO func() gpio.GPIO
+	I2C  func() i2c.I2C
+}
+
+type Describer func(rev int) *Descriptor
+
+var Describers = map[Host]Describer{}
+
+func Describe() (*Descriptor, error) {
+	host, rev, err := Detect()
+	if err != nil {
+		return nil, err
+	}
+
+	describer, ok := Describers[host]
+	if !ok {
+		return nil, errors.New("host: invalid host")
+	}
+
+	return describer(rev), nil
+}

host/detect.go

@@ -1,4 +1,4 @@
-package embd
+package host
 
 import (
 	"fmt"
@@ -10,11 +10,11 @@ import (
 type Host int
 
 const (
-	HostNull Host = iota
-	HostRPi
-	HostBBB
-	HostCubieTruck
-	HostGalileo
+	Null Host = iota
+	RPi
+	BBB
+	CubieTruck
+	Galileo
 )
 
 func execOutput(name string, arg ...string) (output string, err error) {
@@ -51,7 +51,7 @@ func kernelVersion() (major, minor, patch int, err error) {
 	return
 }
 
-func DetectHost() (host Host, rev int, err error) {
+func Detect() (host Host, rev int, err error) {
 	major, minor, patch, err := kernelVersion()
 	if err != nil {
 		return
@@ -69,9 +69,9 @@ func DetectHost() (host Host, rev int, err error) {
 
 	switch node {
 	case "raspberrypi":
-		host = HostRPi
+		host = RPi
 	case "beaglebone":
-		host = HostBBB
+		host = BBB
 	default:
 		err = fmt.Errorf("embd: your host %q is not supported at this moment. please request support at https://github.com/kidoman/embd/issues", node)
 	}

host/rpi/descriptor.go

@@ -7,23 +7,20 @@ import (
 	"github.com/kidoman/embd/i2c"
 )
 
-type descriptor struct {
-	rev int
+func init() {
+	host.Describers[host.RPi] = describer
 }
 
-func (d *descriptor) GPIO() gpio.GPIO {
+func describer(rev int) *host.Descriptor {
 	var pins = rev1Pins
 	if d.rev > 1 {
 		pins = rev2Pins
 	}
 
-	return lgpio.New(pins)
-}
-
-func (d *descriptor) I2C() i2c.I2C {
-	return li2c.New()
-}
-
-func Descriptor(rev int) *descriptor {
-	return &descriptor{rev}
+	return &host.Descriptor{
+		GPIO: func() gpio.GPIO {
+			return lgpio.New(pins)
+		},
+		I2C: li2c.New,
+	}
 }

samples/gpiodetect.go

@@ -4,10 +4,11 @@ import (
 	"time"
 
 	"github.com/kidoman/embd"
+	"github.com/kidoman/embd/host"
 )
 
 func main() {
-	h, _, err := embd.DetectHost()
+	h, _, err := host.Detect()
 	if err != nil {
 		return
 	}
@@ -15,9 +16,9 @@ func main() {
 	var pinNo interface{}
 
 	switch h {
-	case embd.HostBBB:
+	case host.BBB:
 		pinNo = "P9_31"
-	case embd.HostRPi:
+	case host.RPi:
 		pinNo = 10
 	default:
 		panic("host not supported (yet :P)")