waveshare2in13v2: Add function to put controller to sleep

waveshare2in13v2/waveshare213v2.go

@@ -25,6 +25,7 @@ const (
 	driverOutputControl            byte = 0x01
 	gateDrivingVoltageControl      byte = 0x03
 	sourceDrivingVoltageControl    byte = 0x04
+	deepSleepMode                  byte = 0x10
 	dataEntryModeSetting           byte = 0x11
 	swReset                        byte = 0x12
 	masterActivation               byte = 0x20
@@ -301,6 +302,19 @@ func (d *Dev) String() string {
 	return fmt.Sprintf("epd.Dev{%s, %s, Height: %d, Width: %d}", d.c, d.dc, d.opts.Height, d.opts.Width)
 }
 
+// Sleep makes the controller enter deep sleep mode. It can be woken up by
+// calling Init again.
+func (d *Dev) Sleep() error {
+	eh := errorHandler{d: *d}
+
+	// Turn off DC/DC converter, clock, output load and MCU. RAM content is
+	// retained.
+	eh.sendCommand(deepSleepMode)
+	eh.sendData([]byte{0x01})
+
+	return eh.err
+}
+
 // Reset the hardware
 func (d *Dev) reset() error {
 	eh := errorHandler{d: *d}