FreeRTOS Real Time Kernel

Cheers John and Dave for your suggestions. John the interrupt is a specific one for ARM, the undef IRQ happens when a instruction not recognised by the CPU or it's coprocessor(s) is attempted to be executed. Dave you are right, the IRQ link register (R14_undef) contained the return address which was the same as the stack view. This is what I was seeing as 'the functions the undefined IRQ had seemed to jump from'. Thanks for both your help.