diff --git a/README.md b/README.md
index 22a12bd5b..326599d14 100644
--- a/README.md
+++ b/README.md
@@ -241,7 +241,8 @@ and which gives information about the app for the Launcher.
                               // add an icon to allow your app to be tested
 
   "storage": [                // list of files to add to storage
-    {"name":"appid.js",         // filename to use in storage
+    {"name":"appid.js",       // filename to use in storage.
+                              // If name=='RAM', the code is sent directly to Bangle.js and is not saved to a file
      "url":"",                // URL of file to load (currently relative to apps/)
      "content":"..."          // if supplied, this content is loaded directly
      "evaluate":true          // if supplied, data isn't quoted into a String before upload
diff --git a/apps.json b/apps.json
index 7f97b6f84..284116c5e 100644
--- a/apps.json
+++ b/apps.json
@@ -895,6 +895,17 @@
       {"name":"gpsinfo.img","url": "gps-info-icon.js","evaluate": true}
     ]
   },
+  { "id": "assistedgps",
+    "name": "Assisted GPS Update",
+    "icon": "app.png",
+    "version":"0.01",
+    "description": "Downloads assisted GPS data to Bangle.js for faster GPS startup and more accurate fixes",
+    "custom": "custom.html",
+    "tags": "tool,outdoors",
+    "readme": "README.md",
+    "storage": [
+    ]
+  },
   {
     "id": "pomodo",
     "name":"Pomodoro",
diff --git a/apps/assistedgps/ChangeLog b/apps/assistedgps/ChangeLog
new file mode 100644
index 000000000..5560f00bc
--- /dev/null
+++ b/apps/assistedgps/ChangeLog
@@ -0,0 +1 @@
+0.01: New App!
diff --git a/apps/assistedgps/app.png b/apps/assistedgps/app.png
new file mode 100644
index 000000000..970e85139
Binary files /dev/null and b/apps/assistedgps/app.png differ
diff --git a/apps/assistedgps/custom.html b/apps/assistedgps/custom.html
new file mode 100644
index 000000000..e86c660b9
--- /dev/null
+++ b/apps/assistedgps/custom.html
@@ -0,0 +1,113 @@
+<html>
+  <head>
+    <link rel="stylesheet" href="../../css/spectre.min.css">
+  </head>
+  <body>
+
+    <h2>Assisted GPS</h2>
+    <p>GPS can take a long time (~5 minutes) to get an accurate position the first time it is used.
+    AGPS uploads a few hints to the GPS receiver about satellite positions that allow it
+    to get a faster, more accurate fix - however they are only valid for a short period of time.</p>
+    <p>You can upload data that covers a longer period of time, but the upload will take longer.</p>
+    <div class="form-group">
+      <label class="form-label">AGPS Validity time</label>
+      <label class="form-radio">
+        <input type="radio" name="agpsperiod" value="1d" checked><i class="form-icon"></i> 1 day (8kB)
+      </label>
+      <label class="form-radio">
+        <input type="radio" name="agpsperiod" value="2d"><i class="form-icon"></i> 2 days (14kB)
+      </label>
+      <label class="form-radio">
+        <input type="radio" name="agpsperiod" value="3d"><i class="form-icon"></i> 3 days (20kB)
+      </label>
+      <label class="form-radio">
+        <input type="radio" name="agpsperiod" value="1wk"><i class="form-icon"></i> 1 week (46kB)
+      </label>
+    </div>
+    <p>Click <button id="upload" class="btn btn-primary">Upload</button></p>
+
+    <script src="../../core/lib/customize.js"></script>
+
+    <script>
+      // When the 'upload' button is clicked...
+      document.getElementById("upload").addEventListener("click", function() {
+        var radios = document.getElementsByName('agpsperiod');
+        var url = "https://www.espruino.com/agps/assistnow_1d.base64";
+        for (var i=0; i<radios.length; i++)
+          if (radios[i].checked)
+            url = "https://www.espruino.com/agps/assistnow_"+radios[i].value+".base64";
+        console.log("Sending...");
+        //var text = document.getElementById("agpsperiod").value;
+        get(url, function(b64) {
+          var js = jsFromBase64(b64);
+          sendCustomizedApp({
+            storage:[
+              {name:"RAM", content:js},
+            ]
+          });
+        });
+      });
+
+      function UBX_CMD(cmd) {
+        var d = [0xB5,0x62]; // sync chars
+        d = d.concat(cmd);
+        var a=0,b=0;
+        for (var i=2;i<d.length;i++) {
+          a += d[i];
+          b += a;
+        }
+        d.push(a&255,b&255);
+        return d;
+      }
+      function UBX_MGA_INI_TIME_UTC() {
+        var a = new Uint8Array(4+24);
+        a.set([0x13,0x40,24,0]);
+        a.set([ 0x10, // 0: type
+                0,  // 1: version
+                0, // 2: ref - none
+                0x80] ); // 3: leapsecs - unknown
+        var d = new Date();
+        d.setTime(d.getTime()+d.getTimezoneOffset()*60000); // get as UTC
+        var dv = new DataView(a.buffer, 4);
+        dv.setUint16(4, d.getFullYear());
+        dv.setUint8(6, d.getMonth()+1);
+        dv.setUint8(7, d.getDate());
+        dv.setUint8(8, d.getHours());
+        dv.setUint8(9, d.getMinutes());
+        dv.setUint8(10, d.getSeconds());
+        dv.setUint16(16, 10*60); // seconds part of accuracy - 10 minutes
+        return UBX_CMD([].slice.call(a));
+      }
+
+      function jsFromBase64(b64) {
+        var bin = atob(b64);
+        var chunkSize = 128;
+        var js = "\x10Bangle.setGPSPower(1);\n"; // turn GPS on
+        //js += `\x10Bangle.on('GPS-raw',function (d) { if (d.startsWith("\\xB5\\x62\\x05\\x01")) Terminal.println("GPS ACK"); else if (d.startsWith("\\xB5\\x62\\x05\\x00")) Terminal.println("GPS NACK"); })\n`;
+        js += "\x10E.showMessage('Uploading...','AGPS');function p(n) {g.fillRect(0,g.getHeight()-80,g.getWidth()*n,g.getHeight()-60);}";
+        //js += "\x10var t=getTime()+1;while(t>getTime());\n"; // wait 1 sec
+        js += `\x10Serial1.write(atob("${btoa(String.fromCharCode.apply(null,UBX_MGA_INI_TIME_UTC()))}"))\n`; // set GPS time
+        
+        for (var i=0;i<bin.length;i+=chunkSize) {
+          var chunk = bin.substr(i,chunkSize);
+          js += `\x10p(${Math.round(100*i/bin.length)/100});Serial1.write(atob("${btoa(chunk)}"))\n`;
+        }
+        js += "\x10p(1);\n"; // finish progress bar
+        return js;
+      }
+
+      function get(url,callback) {
+        console.log("Loading "+url);
+        var oReq = new XMLHttpRequest();
+        oReq.addEventListener("load", function() {
+          var b64 = this.responseText;
+          console.log("Response received...");
+          callback(b64);
+        });
+        oReq.open("GET", url);
+        oReq.send();
+      }
+
+    </script>
+  </body>
+</html>
diff --git a/core b/core
index c99967381..1b66c4ce1 160000
--- a/core
+++ b/core
@@ -1 +1 @@
-Subproject commit c99967381280f483877c3f11ae7b0d4dc8c53e0e
+Subproject commit 1b66c4ce1ba71036bcb612a2f16bbd7fbc2c66de
diff --git a/testing/GPS-comms.js b/testing/GPS-comms.js
index 38d4c9dde..ca0db16b6 100644
--- a/testing/GPS-comms.js
+++ b/testing/GPS-comms.js
@@ -16,7 +16,7 @@ function writeGPScmd(cmd) {
     a += d[i];
     b += a;
   }
-  d.push(a,b);
+  d.push(a&255,b&255);
   Serial1.write(d);
 }
 function readGPScmd(cmd, callback) {
@@ -131,7 +131,7 @@ function setUBX_MGA_INI_TIME_UTC() {
   dv.setUint8(9, d.getMinutes());
   dv.setUint8(10, d.getSeconds());
   dv.setUint16(16, 10*60); // seconds part of accuracy - 10 minutes
-  writeGPScmd(a.slice());
+  writeGPScmd([].slice.call(a));
 }
 
 setUBX_MGA_INI_TIME_UTC();
