[SeaBIOS] [PATCH] Ctrl-Break support (INT 1B, etc)

[Nikolay Nikolov]

On 07/21/2011 03:51 AM, Kevin O'Connor wrote:
>> I'm new to git (and this is my first SeaBIOS patch ever), so I'm not
>> sure what's the preferred way to submit patches. I just did a "git
>> diff" and attached the result. Sorry if that's not the best way :)
> Best way is to run "git format-patch", but "git diff" is also fine.
> Please do include a "Signed-off-by" line in your commit message or
> email message though.
ok:

Signed-off-by: Nikolay Nikolov <nickysn at users.sourceforge.net>

>> +            asm volatile ("int $0x1B":::"memory");
> Can this use call16_simpint() instead?  If not, calling an interrupt
> should probably backup/restore the register state.
I'm not sure if the registers need to be saved for int 1Bh. I don't know 
what the "spec" says about it. MS-DOS and FreeDOS by themselves 
certainly don't need it - they don't change any of the registers on 
return from their int 1B handlers. Also, the BIOSes I checked didn't 
seem to care about saving any registers before calling int 1B. On the 
other hand, potentially any DOS application might want to install its 
own int 1B handler and we don't know if some of them destroy the values 
in some registers but still happens to work with the most common BIOSes 
(by accident or otherwise). But saving all registers adds an extra 
overhead on the stack that may turn out to be unnecessary? What happens 
if we tell gcc in that inline asm block that all registers may be 
destroyed. Will it increase the overhead on the stack or will it just 
generate slightly less efficient code?
>> +            enqueue_key(0, 0);
> RBIL implies the 0000 should be added to the keyboard buffer before
> the int 0x1B - though I'm not really familiar enough to say which is
> really correct.
I have tested this on several BIOSes and most of them add it after int 
0x1B. These include:

an AWARD BIOS on a GA-K8NF9 mainboard
Insyde H2o BIOS on a Sony VAIO laptop
Microsoft Windows NT/2000/XP/Vista/7's dos box (NTVDM.EXE)
MS-DOS 6.22's own keyb.exe driver, which replaces the BIOS' int 09h handler.

I have also found at least one BIOS, that adds it *before* int 0x1B. 
It's an IBM ThinkPad R30 laptop, with an IBM branded BIOS. Anyhow, I 
assumed that adding it after int 1B is more "standard", because it 
appears to be more common and at least that's what Microsoft does.

Nikolay