make the process of registered available hosts less clunky

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

@@ -0,0 +1,80 @@
+package host
+
+import (
+	"fmt"
+	"os/exec"
+	"strconv"
+	"strings"
+)
+
+type Host int
+
+const (
+	Null Host = iota
+	RPi
+	BBB
+	CubieTruck
+	Galileo
+)
+
+func execOutput(name string, arg ...string) (output string, err error) {
+	var out []byte
+	if out, err = exec.Command(name, arg...).Output(); err != nil {
+		return
+	}
+	output = string(out)
+	return
+}
+
+func nodeName() (string, error) {
+	return execOutput("uname", "-n")
+}
+
+func kernelVersion() (major, minor, patch int, err error) {
+	output, err := execOutput("uname", "-r")
+	if err != nil {
+		return
+	}
+
+	parts := strings.Split(output, ".")
+
+	if major, err = strconv.Atoi(parts[0]); err != nil {
+		return
+	}
+	if minor, err = strconv.Atoi(parts[1]); err != nil {
+		return
+	}
+	if patch, err = strconv.Atoi(parts[2]); err != nil {
+		return
+	}
+
+	return
+}
+
+func Detect() (host Host, rev int, err error) {
+	major, minor, patch, err := kernelVersion()
+	if err != nil {
+		return
+	}
+
+	if major < 3 || (major == 3 && minor < 8) {
+		err = fmt.Errorf("embd: linux kernel versions lower than 3.8 are not supported. you have %v.%v.%v", major, minor, patch)
+		return
+	}
+
+	node, err := nodeName()
+	if err != nil {
+		return
+	}
+
+	switch node {
+	case "raspberrypi":
+		host = RPi
+	case "beaglebone":
+		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)
+	}
+
+	return
+}

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,
+	}
 }