I love the idea of freedom that Coreboot gives, but feel like they should really be using more Asm. I remember doing a comparison a few years ago and CB had far less functionality, while being quite a bit larger, than the standard commercial BIOS for a given machine.
Also, almost all BIOSes go into flat real mode ("unreal mode") not far from the reset entry point, as otherwise they would be unable to access most of the memory and devices in the system.
If you're interested in BIOS stuff one of the things I'd recommend is to get a copy of the PC/AT technical reference - the full BIOS listings are in there, and make for great studying of historical significance since much of the hardware has remained essentially software-compatible since then, only physically changed form. For example, the latest 8-series chipsets for i5/i7 still contain a pair of 8237s, 8259s, and an 8254 in the same configuration as the original AT.
coreboot moves into 32bit protected mode (without paging) within ~30 instructions after power-on. Contemporary PC firmware now does as well, or even moves to 64bit long mode.
For BIOS services, there's SeaBIOS (www.seabios.org) which we can run as a payload. DOS works fine with it.
I'd be more interested in how many cycles it takes. I mean at 2 billion instructions per second, do you really notice a difference between 30 and 10 instructions? However, if any/all/many of the stall on data or something, then yes, it matters.
Also, almost all BIOSes go into flat real mode ("unreal mode") not far from the reset entry point, as otherwise they would be unable to access most of the memory and devices in the system.
If you're interested in BIOS stuff one of the things I'd recommend is to get a copy of the PC/AT technical reference - the full BIOS listings are in there, and make for great studying of historical significance since much of the hardware has remained essentially software-compatible since then, only physically changed form. For example, the latest 8-series chipsets for i5/i7 still contain a pair of 8237s, 8259s, and an 8254 in the same configuration as the original AT.
Here is someone who could boot the very first version of DOS on a Ivy Bridge system: http://www.msfn.org/board/topic/153995-will-ms-dos-3x-run-on...