8254, interrupt

captainstorm · 09-22-2003, 08:00 AM

Hello all,

I have a puzzle here. I have found a couple of different options on the internet on how to program the 8254, and the following are 3 versions to retrive the original init vector.

1. 2. 3.
mov al, 1ch mov al,08h mov al,00h
mov ah, 35h mov ah,35h mov ah,35h
int 21h int 21h int 21h

The first puzzle is: al=00h is the IRQ for timer/counter but al=08h is for real time clock. The example utilize 08h, but why not 00h?

Also I am not sure whether to use al=1ch or al=08h

Thank you all

captainstorm · 09-22-2003, 08:02 AM

Oh, I lost the format, the 1~3 versions should be:
1.
mov al, 1ch
mov ah, 35h
int 21h

2.
mov al,08h
mov ah,35h
int 21h

3.
mov al,00h
mov ah,35h
int 21h

kev82 · 09-22-2003, 08:20 AM

int 0x21 is installed by dos and wont exist unless your running it, for extensive docs on 8254 try here

captainstorm · 09-23-2003, 08:05 AM

Thank you kev, but sorry I do not understand this "won't exist unless your running it". Do you mean int 0x21 is not available under linux? Sorry for this.

captainstorm · 09-23-2003, 10:08 AM

Quote:

Originally posted by kev82
int 0x21 is installed by dos and wont exist unless your running it[/url]

I think the "it" is referring to "DOS". I see.

But are there any ways to treat the interrupt under linux (gas)? I am curious since it makes less sense to me that assembler could not deal with the interrupt. I have searched on the internet but it appears only int 21h 35 and int 21h 25 could do the job.

Any suggestions?
(Thanks again Kev)

kev82 · 09-23-2003, 12:35 PM

you understood correctly, int 0x21 is a service provided by dos and thus only works under dos. however im pretty sure you can program the 8254 from somewhere in /proc i think mplayer uses it to sync video. there is a LinuxGazette article about driving a speaker using the 8254. and the link i gave above has full technical documents on the chip.

captainstorm · 09-24-2003, 08:39 AM

Yeah thanks kev

While actually the application is not a time-critical one. To set time out or something like that. I originally plan to take a chance to learn how to deal with interrupt under linux, but in this typical program, "singal handling" by gcc might also be a good choice.

I have read the datasheet and like a datasheet, its explanation is clear and straight forward. But the things I will look for is the interrupt, which is different from simply "org0004".
A short break