If the timing chain has broken, it will have a very strange sound when you crank it over trying to start it....and the valves will not be going up and down, nor will the cam sensor be turning...if it has jumped a few teeth, it will probably sound a bit different and the compression will be much lower than normal.
to do a chain, you have to get the intercooler out of the way, pull the water pump off, unbolt the balancer, and then remove the front cover...tediou s and a pain in the rear....David could do it in his sleep
Don't panic yet