Jim Stewart wrote:
Chris Arguin wrote:
Off-the-wall idea #132: How much legacy BIOS support do we really need *just* to boot DOS to the point that it loads config.sys and/or autoexec.bat? If we supported just that much, and then had a program you ran (first) in DOS that basically put a legacy BIOS in as if the real BIOS had been shadowed, then we have the best of both worlds. A great BIOS with that supports all the nice boot-stuff w/o too much legacy code, but available legacy code when you need it for DOS.
I can answer that,
Int 10h, function Eh teletype ouput mostly trivial for serial portredirect, done for you with most vga cards Int 11h get equipment config trivial Int 12h mem size trivial Int 13h function 0,1,2 disk read write reset not trivial, probably don't need write for boot, some dos need funct 8 Int 16h function 0,1 keyboard poll and read mostly trivial for serial port redirect, don't know about PC keyboard Int 1Ah function 0,1,2,3 RTC ok if only stub code to return a valid constant - must not return nonsense Int 19h Bootstrap trivial
Why any legacy BIOS support? The answer to this question, in my opinion, highly depends on the hardware and operating systems that are going to be supported.Are those operating systems Intel x86 compatible, then the operating systems fall into three categories:
* real-mode OSs (eg. MS-DOS and the like) * 286-protected mode OSs * 386 protected mode OSs o using segmented model o using flat model
To access PCI BIOS functions, only 386 flat model 386 protected mode OSs (32-bit OSs) do NOT use INT 1Ah. However the calling program does execute a far call to the BIOS entry point. PCI BIOS supports both 16-bit and 32-bit calls.At the other hand if there should be extensive testing in the OpenBIOS (POST), then you are already implementing lots of low-level routines, up to a certain level quite the same as the ints.
You also need the adapter scan stuff if you intend to use vga or disk controllers with on-board bios.
Jim
Can't do without ROM scan if you intend to use video above CGA, SCSI or other adapters with onboard ROM.
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