To: djgpp AT delorie DOT com
Subject: Re: My interrupt handler
References: <7fcm2k$31g$2 AT news DOT luth DOT se>
From: Michael Bukin <M DOT A DOT Bukin AT inp DOT nsk DOT su>
Date: 18 Apr 1999 23:43:40 +0700
In-Reply-To: ams@ludd.luth.se's message of "18 Apr 1999 13:18:12 GMT"
Message-ID: <20iuatubeq.fsf@Sky.inp.nsk.su>
Lines: 29
X-Mailer: Gnus v5.5/Emacs 19.34
Reply-To: djgpp AT delorie DOT com

ams AT ludd DOT luth DOT se (Martin Str|mberg) writes:

> Now I'm back to the basics. Here follows a minimal interrupt handler
> that only chains to the previous one. After that one is installed I
> issue an interrupt just to make sure it's working. Alas it isn't; the
> program stops after inserting the interrupt handler. The last thing it
> prints is "Now.".

> 
> popl %ds
> ljmp %fs:_old_isr

IMHO, it should be %cs:_old_isr.  And you don't need to clobber %fs.

>   new_isr.offset32 = (unsigned long)&handler;
>   asm("movw %%cs, %0": "=g" (new_isr.selector) );

It can be written as

new_isr.selector = _my_cs ();

>   address_of_old_isr = old_isr.offset32;
>   selector_of_old_isr = old_isr.selector;

This is not necessary when using ljmp %cs:_old_isr and
lcall %cs:_old_isr.

-- 
Michael Bukin