A new Garmin Communicator plugin

As part of my plan to create a workout editor, I had to look into the method of communicating between the Garmin plugin and the browser.

It feels like a Java application. It’s documented like it, too. But, it’s written in Prototype, and includes a whole stack of other tools, like XML handling, Ajax communication, and messaging. Things that should belong in seperate parts, IMHO.

So, after a fair bit of plugging around, I was able to make enough sense of it to figure out exactly how it works:

  1. You unlock the plugin with a key-pair
  2. You get a list of devices
  3. If this is a send, then you set the value of a certain property.
  4. You start an Async communication.
  5. You poll the ‘finish’ version of that communication.
  6. When the communication is finished, if this was a receive, you load the data from a property.

I understand why they have made the plugin handle it’s communication in an async manner, but seriously: why not allow for a callback function when the communication is finished? To me, that feels like it would make so much more sense.

Anyway, my other main criticism is that it is inherently unsafe for multiple operations. Instead of, as would be possible with a callback that gets executed when the communication is finished, returning the data, it puts it into a property within the plugin. Which does mean that any bit of code can read it, but also means it’s possible to accidentally overwrite it, as the same property is used for writes.

So, the API for replacing it looks more like:

var plugin = new Garmin.Communicator();
plugin.readActivities(function(data) {
  // data contains the XML activity data.

It’s actually a little more complicated than this: we can pass in delegates, that will have callback methods called when certain events occur. These events are also pushed (using jQuery) onto the HTML element that is the plugin object. But, due to a jQuery bug, you need to listen further up the chain: so you can listen for these events on body.

This script will also add the plugin to the page if it cannot find it, and will run as a singleton: calling the constructor a second time will return the original object, but also add a new delegate to the list of delegates.

I’m tempted to remove the delegate handling, and simply have it as callback-based, but this is sort-of a transition from the way the Garmin team have done it. I’m concerned there may be issues with non-UI initiated read/write events (ie, those that happen on page load) ‘beating’ the plugin being ready, but that is a job for another day.

I’ve also written some Knockout bindings for this: but those are not quite ready for public consumption. I may actually write parsing code for the Training Center Database XML file, and the types it contains, and include that with this project. But, then I may be approaching the bloat seen in the actual Garmin plugin. At this stage, if you have a server that accepts TCX files, then this should be enough.

The project is on BitBucket, as usual: garmin-plugin.

TCX Files and Garmin Goals

I’m partway through writing a workout planning tool: it’s web-based, similar to Garmin Connect, but hopefully with a better interface. I want to be able to create workouts, but I’m really happy with Strava for my activity tracking.

Part of the appeal is being able to export the data to my Garmin Forerunner HRM: this really is one of those ‘scratch my own itch’ tools. So, I’ve had to learn a bit about the Garmin TCX format. There is documentation: it is just an XML file that matches the desired schema.

I’ve made a lot of progress with the workout creation, and even exporting this to TCX. Today, I decided to work on the Goal planning.

Some Garmin HRMs have a neat feature where you can set goals, which the watch will track as you work out. Thus, you could decide you want to run 50km in a given week, and it will show you how far along that goal you are, and how much time you have remaining. However, there is no way on the Forerunner 405cx to set goals on the device, nor with Garmin Training Center, and you have to use Garmin Connect.

The thing is, this part of the TCX file is undocumented. It is stored in the <Extensions> section, and here is my plan to document it a little better.

The basic structure of the file is:

<?xml version="1.0" encoding="UTF-8" standalone="no" ?>


  <Author xsi:type="Application_t">
    <!-- Application info goes here -->

  <ActivityGoals xmlns="http://www.garmin.com/xmlschemas/ActivityGoals/v1">
    <!-- List of goals goes here -->

We are only interested in what happens in the list of goals.

Mostly, a goal is fairly simple:

<ActivityGoal Current="0.0000000" Measure="DistanceMeters" Sport="All" Target="1000.0000000">
  <Name>Run 1km</Name>
  <Period Recurrence="Once">

From this we can see the following fields:

  • Current The amount of Measure that has been completed.
  • Measure The type of goal. Allowable values are: DistanceMeters, TimeSeconds, Calories and NumberOfSessions.
  • Sport You may limit the goal to activities of a given sport. Allowable values are: All, Running, Biking and Other. Note that Garmin Connect will allow you to choose other sports, however, the value will effectively be cast to one of these. Note also that these are the exact same values that are valid for a Workout sport type (with the addition of All).
  • Target What the actual target is.
  • Name The name of this goal. This will not be displayed on a Forerunner 405cx: not sure about other devices.
  • Period Recurrence At this stage, I’m not sure what other values than Once are permitted, but I will be investigating this: this could turn out to be a really nice way to have a repeating weekly goal.
  • StartDateTime, EndDateTime happy to see these in ISO8601 format. Not surprised by that, as the Activity spec stuff (as well as Workout scheduling) is also all in ISO8601.

I do have a couple of comments so far: the HRM watches are essentially timezone aware, and they pull their time from the GPS satellites. I wonder if goals will then respect this: I’m at +0930: if I set a goal to end at 2012-07-21T23:59:59Z, will it finish at that time (which is a UTC timestamp), or will it finish at midnight local time? Can you set goals that finish at other times than midnight?

Initial experiments appear to show no. Setting a time other than 23:59:59 means that the goal is not shown on the device. I don’t see this as a big disadvantage. Testing the timezone-ness of the period is harder: I need to wait until midnight to do so!

Secondly, what values are valid for the recurrence period? This requires some experimentation.

It appears to accept a value of Weekly, but as to if this actually does anything, I’m yet to discover. Considering it has an explicit StartDateTime and EndDateTime, unless the watch extrapolates and updates it, I’m not expecting it to do anything. Certainly, setting an EndDateTime in the past, and choosing Weekly does not appear to have any effect. Again, I’m going to have to wait until midnight clicks over to test this properly. Hopefully, it will update the start and finish times, and reset the current amount.

Also of interest: Garmin Connect sends through a Dummy <X>goal for every goal Measure you do not provide a goal for. However, this is not necessary: removing all but the goals you want to use from the generated TCX file does not prevent sending it to the device, but having an invalid Author block does prevent it from sending.

The Forerunner 405cx will only display one goal of each type (Measure). I believe it shows only the one that is closest to expiring.

When the Garmin agent sends the data to the watch, it removes it from the filesystem. This prevents it being re-sent. When data is recieved from the watch, it appears re-create the activity file from the current goals set up in Garmin Connect. This kind-of makes sense, but is annoying, as any goals that have been set up in Garmin Connect will override the goals created elsewhere.

In practice, it means that in order to send goal data to the device, you must first download the relevant activities, and calculate just how much of each goal has been completed. I was hoping to be able to avoid this: if the watch sent us the goal Current figure, then we could just load this, and apply any changes to targets, without affecting the current value. However, with my device, at least, ActivityGoals are InputToUnit only. At least, if you have no goals in Garmin Connect, it doesn’t send back bogus (dummy) goal data!