Increase ci (#889)

* Change MTU size of BLE transfer packets

This change allows us to monkeypatch the increase in MTU size to
optimize the data transfer rate. Currently, we are setting it at
505, which is the limit the android can accept.

* Allow for Changing the Connection Interval

This change allows us to change the connection interval through
system calls when we obtain the connection handle. It's hacky,
but it accomplishes the task. It's important to note a few things.
First, the Bluetooth specs require that a connection interval as low
as 7.5 ms. Second, there is a 1.25 multiplier on the min & max
settings.

Author: iankchristie

nodejs/FatBeaconPeripheral/FatBeacon.js

@@ -14,6 +14,8 @@ var AdvertisementData =
         require('eddystone-beacon/lib/util/advertisement-data');
 var Eir = require('eddystone-beacon/lib/util/eir');
 var Gatt = require('bleno/lib/hci-socket/gatt');
+var Hci = require('bleno/lib/hci-socket/hci');
+var exec = require('child_process').exec;
 
 var FAT_BEACON_FRAME_TYPE = 0x0e;
 var MAX_URL_LENGTH = 18;
@@ -81,6 +83,55 @@ Gatt.prototype.handleMtuRequest = function(request) {
   return response;
 };
 
+/**
+ * Change the connection interval through commandline tool hcileup. Specs,
+ * allow for a 7.5ms connection interval. Note, there is a 1.25 multiplier
+ * on the min and max values.
+ */
+Hci.changeConnectionInterval = function(handle) {
+  var min = 6;  // Will be multiplied by 1.25.
+  var max = 7;  // Will be multiplied by 1.25.
+  var latency = 0;
+  var timeout = 500;
+
+  var cmd = `hcitool lecup --handle ${handle} --min ${min} --max ${max} ` +
+            `--latency ${latency} --timeout ${timeout}`;
+
+  console.log(cmd);
+
+  exec(cmd, function(error, stdout, stderr) {
+    if(stdout !== null) {
+      console.log('stdout:\t' + stdout );
+    }
+    if(stderr !== null) {
+      console.log('stderr:\t' + stderr);
+    }
+    if(error !== null) {
+      console.log('ERROR:\t' + error);
+    }
+  });
+};
+
+/**
+ * Does the standard processLeConnComplete library behavior, but calls our
+ * custom changeConnectionInterval function to optimize CI.
+ */
+Hci.prototype.processLeConnComplete = function(status, data) {
+  var handle = data.readUInt16LE(0);
+  var role = data.readUInt8(2);
+  var addressType = data.readUInt8(3) === 0x01 ? 'random': 'public';
+  var address = data.slice(4, 10).toString('hex').match(/.{1,2}/g).reverse().join(':');
+  var interval = data.readUInt16LE(10) * 1.25;
+  var latency = data.readUInt16LE(12); // TODO: multiplier?
+  var supervisionTimeout = data.readUInt16LE(14) * 10;
+  var masterClockAccuracy = data.readUInt8(16); // TODO: multiplier?
+
+  Hci.changeConnectionInterval(handle);
+
+  this.emit('leConnComplete', status, handle, role, addressType, address,
+             interval, latency, supervisionTimeout, masterClockAccuracy);
+};
+
 /*********************************************************/
 
 var characteristic = new webpageCharacteristic();