[SOS] frequence timer - QEMU

[anthoine.bourgeois]

Bonjour Adrien,

Je n'ai aucune idée de ce que ça peut être mais je veux
bien y jeter un coup d'oeil.
Peux-tu nous donner le parametre freq et la methode que tu
utilises pour tester la frequence après le changement ?

Cordialement,
Anthoine


> Message du 05/11/08 19:41
> De : "free mail" <lebre.adrien at free.fr>
> A : sos at the-doors.enix.org
> Copie à : 
> Objet : [SOS] frequence timer - QEMU
> 
> 
> Salut,
> 
> J'ai posté sur les mailings list de Qemu (users et dev)
> 
>   Je ne suis pas parvenu à modifier la fréquence du timer PIC8254 en  
> m'appuyant sur le bout de code que a été presenté dans SOS.
> Je pense que le souci vient de Qemu. Je voulais savoir si quelqu'un a  
> deja rencontré ce type de probleme ?
> 
> Merci par avance
> Adrien,
> 
> Pour infos, j'ai poste sur les mailings lists users et dev de qemu. Je  
> n'ai pas vraiment obtenu d'infos pour le moment :
> http://lists.gnu.org/archive/html/qemu-devel/2008-10/msg00384.html
> 
> In the context of study, we have to develop a simple operating system  
> from
> scratch. To develop our ''kernel'' we are using QEMU.
> For few days, we have fighted with the I8254 chip in order to create a  
> timer for
> our system.
> Based on the code provided in the Simple OS
> (http://sos.enix.org/lxr/source/hwcore/i8254.c), we are trying to  
> change the
> frequency.
> Unfortunately, whatever the value of nb_tick, the frequency does not  
> change.
> Here, I just copied the related code. We tried by setting the nb_tick  
> with
> 11931, 1193 and 119 directly in the following functions.  
> Unfortunately, the time
> frequency (according to the IRQ timer handler) is still the same .
> 
> Does anyone have an idea ?
> 
> Thanks in advance,
> Adrien.
> 
> /** 82c54 clock frequency */
> #define I8254_MAX_FREQ 1193180
> 
> /* Ports to communicate with the 82c54 */
> #define I8254_TIMER0  0x40
> #define I8254_TIMER1  0x41
> #define I8254_TIMER2  0x42
> #define I8254_CONTROL 0x43
> 
> ...
> 
> int i8254_set_frequency(unsigned int freq){
>     unsigned int nb_tick;
> 
>     if (freq <= 0)
>        return -255;
> 
>     /* Compute counter value */
>     nb_tick = I8254_MAX_FREQ / freq;
> 
>     /* Counter must be between 1 and 65536 */
>     if (nb_tick > 65536)
>        return -255;
>     if (nb_tick <= 0)
>       return -255;
> 
>     /* The i8254 interprets 0 to mean counter == 65536, because 65536
>        cannot be coded on 16bits */
>     if (nb_tick == 65536)
>       nb_tick = 0;
> 
>     /* We want to configure timer0, we want to send both LSB+MSB to set
>        timer0 freq (-> 0x30), and we configure timer0 in mode 2, ie as a
>        rate generator (-> 0x4) ==> 0x34 */
>     outb(0x34, I8254_CONTROL);
> 
>     /* Send LSB of counter first */
>     outb((nb_tick & 0xFF), I8254_TIMER0);
> 
>     /* Send MSB of counter */
>     outb((nb_tick >> 8) & 0xFF, I8254_TIMER0);
> 
>    return 1;
> }
> 
> 
> Re: i8254 - Cannot change Timer frequency
> by alebre on Wed Sep 17, 2008 4:37 pm
> 
> What is the behavior of QEMU with regard to such instructions ?
> Does QEMU emulate the I8254 chip or does it simply forward the  
> instruction to
> the host OS ? In that case, the host OS could simply does not consider  
> such an
> instruction ?
> 
> Adrien, still looking for some explanations....
> 
> 
> 
> 
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