Bochs Works, Real PC Doesn't

[PlayOS]

Hi,

Just wondering if anyone knew why bochs would work, and a real PC will not?

I have just attempted to run my OS on a real PC and it failed to work. I have been developing it for a while and testing in bochs, but for some reason bochs allows what my PC doesn't.

[Pype.Clicker]

for the same kind of reason it could work on real PC #A and not on real PC #B, including (but not limited to):

• bios aren't same, so one could have extension the other hasn't
• clocks or cycles per instruction aren't same, so timings of CPU vs I/O aren't conserved and some I/O device might go wrong. For instance, some code i wrote for Pentium that used a short jmp to wait for I/O cycle completion didn't work on my new AMD K6-II because that computer had some jump-anticipation hardware that prevented it to flush its pipeline.
• one of the PC don't have a standard hardware (laptops, mostly)
• one has a bug the other hasn't...

welcome to the real world :-/

[PlayOS]

In my code I go into unreal mode, could this be the problem code?

I am going to test this, however I though maybe you have experienced this.

[PlayOS]

OK, this was the problem, now I need to know this (not really need, but more I want to know) how does GRUB get the kernel at 1MB+.

I have looked for the sources for GRUB and this site http://www.gnu.org/software/grub says that it is not realesed to the public yet.

So does anyone know how to get the kernel at or above 1MB, I was thinking that GRUB would read the floppy directly, but that would require alot of code, is this how it does it?

thanks.

[Pype.Clicker]

In my code I go into unreal mode, could this be the problem code?

unreal mode is usually well-supported (though undocumented) by processors ... however, you should not expect your BIOS loads sectors beyond 1Mb barrier successfuly: you need a 2-steps code (first load from floppy using bios into a low-memory area and then move it above 1MB either with the help of unreal mode or through the high-mem-copy feature of BIOS INT15h ...

[PlayOS]

Yeah, I will probably try INT15 because I was loading the kernel in below 1MB and then copying it above so I dont know why it was failing.

[Pype.Clicker]

maybe you can also try to find a program that _do_ use unreal mode and see if it runs on your machine ...

[K.J.]

GRUB switches from PMode to Real Mode over and over again in it's code so that it can use BIOS interrupts yet still get the OS loaded @ the 1MB mark. You can see the code for GRUB here:
http://savannah.gnu.org/cgi-bin/viewcvs/grub/grub/

K.J.

[Pype.Clicker]

oh, and just to mention ... My own OS works pretty fine on real hardware, but on BOCHS (unknown version - about 4 monthes aged ?), it just freezes the main processing task once the CLOCK has been pushed to 1KHz !??

any clue ? do someone know how i could see where the hang occurs ? the keyboard IRQ are still processed ... maybe i just asked for a too fast clock and have no time to process anything else (would be weird, though ...)

[Tom]

Well...my FritzOS won't EVEN boot with bochs...a Linux Seg Fault happens just when it starts reading the floppy...

I can't wait for Bochs 2...

[Tom]

YES YEA!!!!!!

Bochs Pre 2 boots FritzOS!!!!!!!!!!!

Never mind whatever I said about bochs!

2 is wonderful!!!!!

No more reboot -f's!!!!!

;D ;D ;D ;D ;D ;D ;D ;D ;D ;D ;D ;D ;D ;D ;D ;D ;D ;D ;D ;D ;D ;D ;D ;D ;D ;D ;D ;D ;D