How can I create a custom XML feed?

I have not done an XML feed in codeigniter but I am sure you will have no problems at all.

XML is just an alternative markup language like HTML (but not HTML) which was designed specifically for transferring data.

So your controller just collects your data as it would for a normal page, and loads a view that has xml markup rather than html markup. The url to that controller is then your feed url. If you visit it in a browser it is not very pretty, but it is not HTML.

Hope that helps,

Paul.