Include the datasource-pollable extension in your Y.use() statement to add the setInterval(), clearInterval(), and clearAllInterval() methods to all your DataSource instances.

YUI().use("datasource-function", "datasource-polling", function(Y) {
    var myFunction = function() {
            return new Date();
        },
        myDataSource = new Y.DataSource.Function({source:myFunction}),
        request = {
            callback: {
                success: function(e){
                    Y.one("#demo_output_polling")
                     .setHTML("At the tone the time will be: " +
                                Y.dump(e.response.results[0].toString()));
                },
                failure: function(e){
                    Y.one("#demo_output_polling")
                     .setHTML("Could not retrieve data: " + e.error.message);
                }
            }
        },
        id = myDataSource.setInterval(1000, request); // Starts polling

        myDataSource.clearInterval(id); // Ends polling
});