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[ALSA] usb-audio: use 1 ms URBs when capturing 

USB generic driver
When capturing audio data, we do not know beforehand how many samples
the device sends per frame, so we have to use URBs that are as short as
possible to make sure that we can handle period boundaries without any
additional latencies.

Furthermore, the total count of URBs submitted doesn't matter when
capturing, so we can just use the maximum number.

Signed-off-by: Clemens Ladisch <clemens@ladisch.de>
This commit is contained in:
Clemens Ladisch 2005-08-12 08:25:26 +02:00 committed by Jaroslav Kysela
parent a53fc188ec
commit 15a24c0778
1 changed files with 12 additions and 6 deletions
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18
sound/usb/usbaudio.c
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@ -97,7 +97,7 @@ MODULE_PARM_DESC(async_unlink, "Use async unlink mode.");
#define MAX_PACKS 10
#define MAX_PACKS_HS (MAX_PACKS * 8) /* in high speed mode */
#define MAX_URBS 5 /* max. 20ms long packets */
#define MAX_URBS 8
#define SYNC_URBS 4 /* always four urbs for sync */
#define MIN_PACKS_URB 1 /* minimum 1 packet per urb */
@ -920,10 +920,12 @@ static int init_substream_urbs(snd_usb_substream_t *subs, unsigned int period_by
else
subs->curpacksize = maxsize;
if (snd_usb_get_speed(subs->dev) == USB_SPEED_FULL)
if (is_playback)
urb_packs = nrpacks;
else
urb_packs = (nrpacks * 8) >> subs->datainterval;
urb_packs = 1;
if (snd_usb_get_speed(subs->dev) == USB_SPEED_HIGH)
urb_packs = (urb_packs * 8) >> subs->datainterval;
/* allocate a temporary buffer for playback */
if (is_playback) {
@ -935,9 +937,13 @@ static int init_substream_urbs(snd_usb_substream_t *subs, unsigned int period_by
}
/* decide how many packets to be used */
total_packs = (period_bytes + maxsize - 1) / maxsize;
if (total_packs < 2 * MIN_PACKS_URB)
total_packs = 2 * MIN_PACKS_URB;
if (is_playback) {
total_packs = (period_bytes + maxsize - 1) / maxsize;
if (total_packs < 2 * MIN_PACKS_URB)
total_packs = 2 * MIN_PACKS_URB;
} else {
total_packs = MAX_URBS * urb_packs;
}
subs->nurbs = (total_packs + urb_packs - 1) / urb_packs;
if (subs->nurbs > MAX_URBS) {
/* too much... */