implemented USB HID composite keyboard support

src/machine/usb/hid.go

@@ -0,0 +1,42 @@
+package usb
+
+import (
+	"errors"
+)
+
+var (
+	ErrHIDInvalidPort    = errors.New("invalid USB port")
+	ErrHIDInvalidCore    = errors.New("invalid USB core")
+	ErrHIDReportTransfer = errors.New("failed to transfer HID report")
+)
+
+type HID struct {
+	Port int
+	core *core
+}
+
+type HIDConfig struct {
+	// Port is the MCU's native USB core number. If in doubt, leave it
+	// uninitialized for default (0).
+	Port int
+}
+
+func (hid *HID) Configure(config HIDConfig) error {
+
+	if config.Port >= CoreCount || config.Port >= dcdCount {
+		return ErrHIDInvalidPort
+	}
+	hid.Port = config.Port
+
+	// verify we have a free USB port and take ownership of it
+	var st status
+	hid.core, st = initCore(hid.Port, class{id: classDeviceHID, config: 1})
+	if !st.ok() {
+		return ErrHIDInvalidPort
+	}
+	return nil
+}
+
+func (hid *HID) Keyboard() *Keyboard {
+	return hid.core.dc.keyboard()
+}