Re: hw_rule

[Takashi Iwai <tiwai@suse.de>]

At 08 May 2003 23:19:28 +0000,
Giuliano Pochini wrote:
> 
> 
> I wrote this rule:
> 
> 
> static int hw_rule_format_set_channels(snd_pcm_hw_params_t *params,
> snd_pcm_hw_rule_t *rule) {
>   snd_interval_t *c=hw_param_interval(params,
> SNDRV_PCM_HW_PARAM_CHANNELS);
>   snd_mask_t *f=hw_param_mask(params, SNDRV_PCM_HW_PARAM_FORMAT);
>   snd_interval_t ch;
> 
>   printk("Rule f=%x %x %x\n", f->bits[0], f->bits[1], f->bits[2]);
>   memset(&ch, 0, sizeof(ch));
> 
>   // S32_BE is mono only
>   if (f->bits[0]==SNDRV_PCM_FMTBIT_S32_BE) {
>     ch.min=1;
>     ch.max=1;
>     ch.integer=1;
>     return(snd_interval_refine(c, &ch));
>   }
>   // U8 and S16_LE are stereo only
>   if (f->bits[0]==SNDRV_PCM_FMTBIT_U8 ||
>       f->bits[0]==SNDRV_PCM_FMTBIT_S16_LE) {
>     ch.min=2;
>     ch.max=2;
>     ch.integer=1;
>     return(snd_interval_refine(c, &ch));
>   }
>   // S32_LE supports any number of channels.
>   return(0);
> }
> 
> 
> It seems to work, but since it's based on other drivers (no docs...),
> there are some thing I don't know:
> - Is f->bits[0] correct ?  All formats supported by the card are < 31. I
> suppose formats >=32 go in bits[1], isn't it ?

yes.  but over 32 is rarely used.

> - what are ch.openmin, openmax, empty ?  They are taken into account
> because if I don't clear the structure the rule doesn't work anymore.

openmin/openmax are the minimum and maximum value but the
configuration cannot be exactly these values.
empty is set if the configuration is empty.

> - How many stupid bugs are there ? :)

i see only subtle issues.
it's better to use snd_interval_any() instead of memset().
the resultant interval_t would accept all values.

the constraint for the another direction would be needed, too,
that is, the constraint for the channels which checks the acceptable
formats from the current values.


ciao,

Takashi


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