It is mentioned on the IDA Pro Hex-Rays site under decompiler error messages
16-bit functions are not supported
It goes on to say:
The decompiler itself CAN be fine tuned to decompile 16-bit code, however this is not a priority for now.
Does anyone know how to "fine-tune" the decompiler in this way?
That is meant to say that the developers at Hex-Rays can fine tune the decompiler code to work on 16-bit code, but it is not a priority for them right now.
It would be non-trivial for an end-user without the decompiler's source code to fine-tune the decompiler plugin. But, if you feel you're up for the challenge, go for it! :)
