Re: [alsa-devel] [PATCH 1/5] ALSA: snd-usb: implement new endpoint streaming model

Daniel Mack wrote:

+++ b/sound/usb/card.h +struct snd_usb_endpoint {

• struct snd_usb_endpoint *sync_slave;

In theory, there could be more than one slave.

+struct snd_usb_endpoint *snd_usb_add_endpoint(struct snd_usb_audio *chip, ...

• /* select the alt setting once so the endpoints become valid */
• snd_printk("%s() calling usb_set_interface()\n", __func__);
• usb_set_interface(ep->chip->dev, ep->iface, ep->alt_idx);

This needs error handling.

+void snd_usb_endpoint_activate(struct snd_usb_endpoint *ep) +{

• usb_set_interface(ep->chip->dev, ep->iface, ep->alt_idx);
  

This too.

+void snd_usb_handle_sync_urb(struct snd_usb_endpoint *ep, +{

• for (i = 0; i < in_ctx->packets; i++) {
  

• 	if (urb->iso_frame_desc[i].status == 0)
  

• 		out_ctx->packet_size[i] =
  

• 			urb->iso_frame_desc[i].actual_length / ep->stride;
  

• 	else
  

• 		out_ctx->packet_size[i] = 0;
  

When there is any error in any received packet (status != 0), we do not know how many frames to send. Sending zero frames is certain to be wrong and will break synchronization between the two streams.

As far as I can see, the only way to handle such errors is to stop the stream(s) and the PCM device(s).

Regards, Clemens