Posted by Perna
"It looks like a lot of people getting confused about this. Here is what works now:
If you run PX4 flight stack on your FC it is now able to talk direct to crossfire, core pro, blackbox by BST. PX4 will provide BST frames like current senor ( battery, current, capacity ), GPS ( the same data like the TBS GPS ) and attitude ( artificial horizon ). For all who run a blackbox I would not touch it ( never touch a running system
).
For all core pro and crossfire users this gives you the ability to get all relevant information direct from your FC and you will have the same features available like you have by connecting a TBS GPS and TBS current sensor to your crossfire ( latest coordinates on the crossfire OLED, MAVLink emulator with real time position tracking on any MAVLink GCS ). With a GPS source it's also much more easy to find your lost plane again. Due the internal battery it will always send you the latest recorded coordinates as soon as you get into crossfire range.
This update does not cover full telemetry like upload waypoints or configure your FC. Full MAVLink support will come with the next crossfire update. It's just an interface who makes PX4 talk BST with the frames mentioned above.
APM, PX4, Pixhawk...
Pixhawk, Pixhack, PixFalco are the hardware and APM and PX4 is the software you run on those FCs. All of them can run both APM and PX4
http://diydrones.com/forum/topics/differences-between-apm-px4-pixhawk
APM could actually merge this code as they use the same driver sets.
MAVLink inside crossfire.
It my be confusing because you can connect to the crossfire TX by the same GCS ( APM Planner, Droid Planner, QGroundControl ) you can configure your FC and plan missions but not yet over crossfire.
This is why the crossfire TX is emulating an FC internally to make it work with already existing tools and apps. Due the low bandwidth but great range we are really limited in sending data up and down. So we decided to send only the most important stuff back to the crossfire TX. The link is not capable of sending all FC frames up and down. Up to crossfire version V1.09 Mavlink is only to see live tracking of your wing/copter on a MAVLink GCS.
With the next update we are going to change this. We are going to merge a data radio inside crossfire so you have all features you are used to have with your MAVLink data radio. This means an additional data radio will be not required anymore and everything FC related can also be done direct over crossfire.
I hope this helps to figure out how it works now and how it will work any time soon
"