BOSSA is a flash programming utility for Atmel's SAM family of flash-based ARM microcontrollers. The motivation behind BOSSA is to create a simple, easy-to-use, open source utility to replace Atmel's SAM-BA software. BOSSA is an acronym for Basic Open Source SAM-BA Application to reflect that goal.
The chip ID's for the ATSAM4SD16 series are incorrect. See the datasheet, page 561.