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OS hangs on initializing HAL.
Posted: Thu Nov 22, 2012 10:24 am
by drunkenfox
I decided to start my OS based on broken thorn's OS dev series. I modified the interface to my liking and changed file names a little bit. I also added debug messages to the kernel startup to diagnose problems. I can run it fine in virtual box because it quickly goes to the prompt after initializing HAL, interrupts, ect. However, when I run it on a real hardware it just hangs at initializing the HAL code. I can't seem to figure out why
](./images/smilies/eusa_wall.gif "Brick wall")
I have uploaded the source @
https://www.dropbox.com/s/9tx3rt13x994b98/otdos.zip
Re: OS hangs on initializing HAL.
Posted: Thu Nov 22, 2012 10:47 am
by bluemoon
This is indeed the result one would expect. You did not expect it to run on real hardware on first attempt, do you?
Some common problem on running test OS (especially tutorials) real hardware is having assumptions - assume hardware(eg. PS2 controller, A20) exists, or accessible at special location.
Re: OS hangs on initializing HAL.
Posted: Thu Nov 22, 2012 2:24 pm
by gerryg400
If it hangs, it should be trivial to find out at which instruction it hangs. Even in a programme 1 million lines long you should be able to use a 'divide and conquer' method and find your problem within 20 guesses. Have you done that yet ?
From there, it should be simple to see what's wrong and fix it.
Re: OS hangs on initializing HAL.
Posted: Thu Nov 22, 2012 3:11 pm
by mich
The HAL initialization has only 6 points where it could "hang":
Code: Select all
int _cdecl hal_initialize () {
//! disable hardware interrupts
disable ();
//! initialize motherboard controllers and system timer
i86_cpu_initialize ();
i86_pic_initialize (0x20,0x28);
i86_pit_initialize ();
i86_pit_start_counter (100,I86_PIT_OCW_COUNTER_0, I86_PIT_OCW_MODE_SQUAREWAVEGEN);
//! enable interrupts
enable ();
return 0;
}
Like gerryg400 suggested use some output functionality (like printf(), or even an LED would do) to determine at which of those 6 points it "hangs". Then recursively apply that strategy to the functions being called until you end up at the exact instruction it all goes wrong.
Re: OS hangs on initializing HAL.
Posted: Sat Nov 24, 2012 11:59 am
by drunkenfox
It appears to hang on enabling interrupts, or when returning back to init() in the kernel.
Output:
Code: Select all
Starting OT-DOS...
Initializing HAL
Disabling interrupts
Enabling interrupts
It ceases to move on.
Re: OS hangs on initializing HAL.
Posted: Sat Nov 24, 2012 12:29 pm
by mich
ponyboy wrote:It appears to hang on enabling interrupts, or when returning back to init() in the kernel.
You can place an output function call right in front of the return in hal_initialize() and then another one right after the call to hal_initialize() in init(). That way you can figure out whether it is either or.
Re: OS hangs on initializing HAL.
Posted: Sat Nov 24, 2012 12:40 pm
by drunkenfox
Found out that it hangs on enabling interrupts (which is just '_asm sti'). I don't know why it would happen though.
Re: OS hangs on initializing HAL.
Posted: Sat Nov 24, 2012 7:00 pm
by mich
ponyboy wrote:Found out that it hangs on enabling interrupts (which is just '_asm sti'). I don't know why it would happen though.
Maybe it doesn't hang it just happens to receive an interrupt and then wander off into the interrupt handler. Does an interrupt handler exist?
Will the code run if you don't enable the interrupt there?
If so will it "hang" when you enable the interrupt later on?
Is the HAL initialized appropriately and correctly? (See bluemoon's post)
Re: OS hangs on initializing HAL.
Posted: Sun Nov 25, 2012 11:48 am
by neon
Hello,
The error is most probably the interrupt handler for the PIT itself. The typical censuses is to write the actual interrupt handler in assembly language rather then C to prevent problems caused by the compiler and increases portability (no need for odd stack manipulation that can break between compiler versions or compiler extensions.) If you really prefer to use C for the interrupt handler, though, I recommend making it a naked function and getting rid of your stack changes:
Code: Select all
/* note: __declspec(naked) is MSVC specific. It is better to write
this in assembler, or use a generic ISR stub in assembler that calls your C handler */
__declspec(naked) void _cdecl i86_pit_irq () {
//! increment tick count
_pit_ticks++;
//! tell hal we are done
interruptdone(0);
}