EXC_RETURN when is floating point stack save?

On the M4F when does the EXC_RETURN  bit[4] get cleared to indicate the floating point stack is saved? 

Specifically does the core push the floating point stack (S0-S15) on the stack anytime the floating point hardware is enabled or does it do it only when a floating point operation is in process and the exception occurs? 

Thanks

Trampas

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