Hi,
There's at least one USB audio chipset out there which supports only one
non-standard rate (ID 0e6a:0310 supports 46875Hz). There's a few other
patches for this card which are unsatisfactory because they attempt to
map this rate to 44.1k leading to sound distortion.
The patch below uses SNDRV_PCM_RATE_KNOT to properly support the
non-standard rates where they are available.
Cheers,
Luke
--- usbaudio.c.b4 2006-08-05 15:22:17.000000000 +0100
+++ usbaudio.c 2006-08-05 15:05:43.000000000 +0100
@@ -119,6 +119,7 @@
unsigned int rate_min, rate_max; /* min/max rates */
unsigned int nr_rates; /* number of rate table entries */
unsigned int *rate_table; /* rate table */
+ unsigned int needs_knot; /* any unusual rates? */
};
struct snd_usb_substream;
@@ -1727,6 +1728,8 @@
}
channels[f->format] |= (1 << f->channels);
rates[f->format] |= f->rates;
+ /* needs knot? */
+ if (f->needs_knot) goto __out;
}
/* check whether channels and rates match for all formats */
cmaster = rmaster = 0;
@@ -1767,6 +1770,35 @@
return err;
}
+/*
+ * If the device supports unusual bit rates, does the request meet these?
+ */
+static int snd_usb_pcm_check_knot(struct snd_pcm_runtime *runtime, struct snd_usb_substream *subs)
+{
+ struct list_head *p;
+ struct snd_pcm_hw_constraint_list constraints_rates;
+ int err;
+
+ list_for_each(p, &subs->fmt_list) {
+ struct audioformat *fp;
+ fp = list_entry(p, struct audioformat, list);
+
+ if (!fp->needs_knot) continue;
+
+ constraints_rates.count = fp->nr_rates;
+ constraints_rates.list = fp->rate_table;
+ constraints_rates.mask = 0;
+
+ err = snd_pcm_hw_constraint_list(runtime, 0,
+ SNDRV_PCM_HW_PARAM_RATE,
+ &constraints_rates);
+
+ if (err < 0) return err;
+ }
+
+ return 0;
+}
+
/*
* set up the runtime hardware information.
@@ -1829,6 +1861,8 @@
SNDRV_PCM_HW_PARAM_CHANNELS,
-1)) < 0)
return err;
+ if ((err = snd_usb_pcm_check_knot(runtime, subs)) < 0)
+ return err;
}
return 0;
}
@@ -2366,6 +2401,7 @@
unsigned char *fmt, int offset)
{
int nr_rates = fmt[offset];
+ int found = 0;
if (fmt[0] < offset + 1 + 3 * (nr_rates ? nr_rates : 2)) {
snd_printk(KERN_ERR "%d:%u:%d : invalid FORMAT_TYPE desc\n",
chip->dev->devnum, fp->iface, fp->altsetting);
@@ -2388,6 +2424,7 @@
return -1;
}
+ fp->needs_knot = 0;
fp->nr_rates = nr_rates;
fp->rate_min = fp->rate_max = combine_triple(&fmt[8]);
for (r = 0, idx = offset + 1; r < nr_rates; r++, idx += 3) {
@@ -2396,13 +2433,19 @@
fp->rate_min = rate;
else if (rate > fp->rate_max)
fp->rate_max = rate;
+ found = 0;
for (c = 0; c < (int)ARRAY_SIZE(conv_rates); c++) {
if (rate == conv_rates[c]) {
+ found = 1;
fp->rates |= (1 << c);
break;
}
}
+ if (!found) {
+ fp->needs_knot = 1;
+ }
}
+ if (fp->needs_knot) fp->rates |= SNDRV_PCM_RATE_KNOT;
} else {
/* continuous rates */
fp->rates = SNDRV_PCM_RATE_CONTINUOUS;
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