[alsa-devel] [PATCH] US-122L Driver, v0

[Karsten Wiese]

Am Donnerstag, 8. November 2007 schrieb Clemens Ladisch:
> 
> I'm using the 8-microframes alignment because ehci-hcd configures the
> controller to interrupt at most every 1 ms.  It has a module option to
> change this, but as long as snd-usb-audio cannot detect a lower setting,
> it would not make sense to allow shorter periods.

For an 1ms interrupt alignment ehci-hcd must be loaded with non-default
parameters.
In ehci-hcd.c as of 2.6.23:

/* Initial IRQ latency:  faster than hw default */
static int log2_irq_thresh = 0;		// 0 to 6
module_param (log2_irq_thresh, int, S_IRUGO);
MODULE_PARM_DESC (log2_irq_thresh, "log2 IRQ latency, 1-64 microframes");

That makes a default IRQ latency of 1/8ms. This is also what I see here:
The us122l driver works with 64frames/period 2 periods at 96kHz sample rate.
Thats about 1400 interupts/s. Wouldn't be possible with 1ms alignment.

kind regards,
      Karsten