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  • IMxxxxxxxxxx directories are described in the 1998 JEIDA (Japan Electronic Industry Development Association) patent
  • IMxxxxxxxxxx are referred to as an 'Exif directory'.
  • Exif directories can store Exif files. It's difficult to understand exactly what the paper says, but it's clear that this folder is used for general purpose file (image, sound, video) manipulation.
  • In Fujifilm cameras, an S3 file is stored in the IMFIDX10 directory. For the XF1, it is C:\IMFIDX10\XF10RS.S3.
  • In the JEIDA paper, IMFIDX10 is described as a 'self-recorded Exif directory'.
  • S3 files are standard Motorola S-record files. Fujifilm has a long history of using these files. On cameras from the early 2000s, they were used to apply early firmware updates.
  • These files appear on Fujifilm cameras as far back as the S3 Pro to the XH2S (C:\IMFIDX10\LX46.S).
  • See /etc/s3 for a lousy attempt to understand S3 files.

The S3 file reader seems to apply patches to EEPROM (possibly allowing script execution, TGKAI stuff), and possibly write bytes to RAM or flash memory. It is called by a function table handler that can be traced back to the usbcont task. This means it could possibly be triggered via USB. It's impossible to tell because of how cryptic the RTOS is.