On Tue, May 11, 2010 at 12:06:09PM -0400, Alan Stern wrote: > On Wed, 12 May 2010, FUJITA Tomonori wrote: > > > > > Can you tell me all the exact process of DMA that the usb core and the > > > > driver do? > > > > > > 1. The audio driver stores data in urb->transfer_buffer. > > > > How urb->transfer_buffer is allocated? > > By kmalloc(). Right, Daniel? Yes, and that's precisely the reason for the whole thread ;) [...] > > The driver does only DMA_TO_DEVICE? Or you see DMA problems only with > > DMA_TO_DEVICE? > > The particular test that Pedro is running uses audio output only -- > he's sending sound data to a speaker and it comes out noisy. > > But the audio data has to come from somewhere, and I don't remember > where. Pedro, does the noise occur only when you're playing sound that > comes from a different USB device? What happens if you play sounds > that are stored on your hard disk, like an MP3 file? AFAIK that was playback from a file, yes. It would be interesting to have some results for the other direction as well, that's true. Thanks, Daniel -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
