1. A method of performing background processing in a multithreaded digital signal processor comprising a plurality of processing threads, said method comprising: forming a background thread interrupt as one of a plurality of interrupt types, said background thread interrupt to initiate a background process using one of a plurality of processing threads of said multithreaded digital signal processor; storing said background thread interrupt in an interrupt register; forming a background processing mask; and associating said background processing mask with at least a subset of said plurality of processing threads; sensing a predetermined event in an active thread of said plurality of processing threads during processing of said multithreaded digital signal processor; issuing said background thread interrupt from said interrupt register in response to said predetermined event; initiating background processing using an idle thread of said subset of said plurality of processing threads having an associated background process mask, wherein said multithreaded digital signal processor is operable to support concurrent execution of two or more of said plurality of processing threads; storing said background thread interrupt as a background prefetch interrupt; forming said background processing mask as a background prefetch processing mask; and initiating said background processing as background prefetch processing.