No working solution update right now, but analyzing the BIOS dump file i found out that the 128Kb BIOS FLASH contains:
- VGA BIOS (marked 55AA as option rom)
- (EXTENDED) BIOS Utility for configuration
- The actual BIOS defining the interrupts and POST.
Luckily it turns out that IDA (a great disassembler) has its 7.0 released as freeware for x64. It works also for 16bit real mode.
Some strings are found that shows hidden options, I also noted some LPT (0x378) and COM port (int 14h) communication during startup.
For the CF Card modification i will need to alter:
- The visual setup thing to select the CF Card mode and save it to NV RAM.
- The actual BIOS/POST setting the right contents where DOS can find the HDD info.