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