[quote user="Ant Scranney"]Just tried this in a Stellaris program that runs ok. With the debug window opened I click the run menu, then scroll down to clock, but all the options are "grey'ed out" [/quote]
Please see this wiki page for information on how to measure clock cycles on Stellaris devices:
http://processors.wiki.ti.com/index.php/Watchpoints_for_Stellaris_in_CCS#Configure_a_Count_Event