: So, you're not actually writing BIOS code -- you're just wanting to
: look at some of the data that the BIOS has already stored.
No, not exactly. I am modifying an existing local module for the BIOS (custom BCM) that is called from the main bios code after completion and before the OS, which resides on a compact flash, is loaded. My code, which is loaded at 0D000h, calculates an MD5 over itself as well as certain values that are stored beginning at bios address 60000h; these values are stored there by an offline utility program when the BIOS chip is created. The data stored there includes an MD5 of the bios itself and of the OS compact flash, etc. If the calculated MD5 does not match the pre-stored value, then I issue an error message and do not load the OS.
I have verified that the entire 80000h bytes of the bios can be read from addresses 0xFFF80000-0xFFFFFFFF as this is either an exact image of the bios chip or the bios chip ROM itself (I'm not sure which.) In either case, I figure that if I can switch the CPU into protected mode from my bios code, I should be able to read what I need from that upper memory.
Another complication which is probably superfluous to this discussion, but is important nonetheless, is that the BCM binary plus my module's binary are compressed by a program MKROM.exe from Whizpro Technology, which apparently no longer exists so I have been unable to contact them to ask questions. There is a website http://www.whizpro.com.tw
which appears to be abandoned, as the only email contact there is inactive. If it were not for this compression, the data stored at 0x60000 could be stored internal to my module by the offline utility program and there would be no problem.
I must admit that, although I have been writing code for over 40 years, this is one of the more challenging projects I have encountered. It is my first foray into the bios so obviously I'm not an expert in that area, but expect that I will be before this is done. -:)
Thanks again Bret, for your help.