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// Host descriptor data structures.
package embd
import (
// Descriptor represents a host descriptor.
type Descriptor struct {
GPIODriver func() GPIODriver
I2CDriver func() I2CDriver
LEDDriver func() LEDDriver
SPIDriver func() SPIDriver
// The Describer type is a Descriptor provider.
type Describer func(rev int) *Descriptor
// Describers is a global list of registered host Describers.
var describers = make(map[Host]Describer)
// Register makes a host describer available by the provided host key.
// If Register is called twice with the same host or if describer is nil,
// it panics.
func Register(host Host, describer Describer) {
if describer == nil {
panic("embd: describer is nil")
if _, dup := describers[host]; dup {
panic("embd: describer already registered")
describers[host] = describer
glog.V(1).Infof("embd: host %v is registered", host)
var hostOverride Host
var hostRevOverride int
var hostOverriden bool
// SetHost overrides the host and revision no.
func SetHost(host Host, rev int) {
hostOverride = host
hostRevOverride = rev
hostOverriden = true
// DescribeHost returns the detected host descriptor.
// Can be overriden by calling SetHost though.
func DescribeHost() (*Descriptor, error) {
var host Host
var rev int
if hostOverriden {
host, rev = hostOverride, hostRevOverride
} else {
var err error
host, rev, err = DetectHost()
if err != nil {
return nil, err
describer, ok := describers[host]
if !ok {
return nil, fmt.Errorf("host: invalid host %q", host)
return describer(rev), nil
// ErrFeatureNotSupported is returned when the host does not support a
// particular feature.
var ErrFeatureNotSupported = errors.New("embd: requested feature is not supported")
// ErrFeatureNotImplemented is returned when a particular feature is supported
// by the host but not implemented yet.
var ErrFeatureNotImplemented = errors.New("embd: requested feature is not implemented")