In some (or all, I wouldn't know) firmwares there exists compressed code that has been guessed to be code for loading to DSP program memory at startup. AFAIK, little has been done to investigate this.
jp52_firmware build#0014 2005/01/31 Akihiro Uehara, Satoshi Naito, Yukio Chib
This is associated with a binary blob that is clearly not ARM code. In a540, this is associated with sub_FFC79AFC
launcher.s rev-1.0 2001/07/17 author Satoshi Naitod
The .s suggests some kind of object built from assembler code, but again, clearly not ARM.
The similar blobs exist in later cameras, with less of the identifying strings.
Some (possibly) related string "JPEGICError", "JpCore.c", "JpCoreIntrHandler", "SUBCPU SIO FAILED"
I've always assumed the EngDrv* functions were related to controlling the other half of digic.