From 15a24c0778e9bdd48d8e1cf60a263837b5c30ed5 Mon Sep 17 00:00:00 2001 From: Clemens Ladisch Date: Fri, 12 Aug 2005 08:25:26 +0200 Subject: [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 --- sound/usb/usbaudio.c | 18 ++++++++++++------ 1 file changed, 12 insertions(+), 6 deletions(-) diff --git a/sound/usb/usbaudio.c b/sound/usb/usbaudio.c index 8298c462c29..9e38d3d1322 100644 --- a/sound/usb/usbaudio.c +++ b/sound/usb/usbaudio.c @@ -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... */ -- cgit v1.2.3