Add callback to stopPoll

Author: kevinmehall

Readme.md

@@ -219,10 +219,11 @@ the kernel at all times to ensure continuous data flow. This is handled by the
 libusb event thread, so it continues even if the Node v8 thread is busy. The
 `data` and `error` events are emitted as transfers complete.
 
-### .stopPoll()
+### .stopPoll(cb)
 Stop polling.
 
-Further data may still be received. The `end` event is emitted once all transfers have completed or canceled.
+Further data may still be received. The `end` event is emitted and the callback
+is called once all transfers have completed or canceled.
 
 ### Event: data(data : Buffer)
 Emitted with data received by the polling transfers

usb.js

@@ -247,14 +247,15 @@ Endpoint.prototype.startPoll = function(nTransfers, transferSize, callback){
 	return transfers;
 }
 
-Endpoint.prototype.stopPoll = function(){
+Endpoint.prototype.stopPoll = function(cb){
 	if (!this.pollTransfers) {
 		throw new Error('Polling is not active.');
 	}
 	for (var i=0; i<this.pollTransfers.length; i++){
 		this.pollTransfers[i].cancel()
 	}
 	this.pollActive = false
+	if (cb) this.once('end', cb);
 }
 
 function InEndpoint(device, descriptor){