RTI

from Jargon File (4.4.4, 14 Aug 2003)

RTI
 /R.T.I/, interj.

   The mnemonic for the `return from interrupt' instruction on many
   computers including the 6502 and 6800. The variant RETI is found among
   Z80 hackers. Equivalent to "Now, where was I?" or used to end a
   conversational digression. See {pop}.

from The Free On-line Dictionary of Computing (8 July 2008)

RTI
RETI

   {Return from interrupt}

from V.E.R.A. -- Virtual Entity of Relevant Acronyms (June 2006)

RTI
       ReTurn from Interrupt