Ask a question about TI AM1808 usb-host-controler.

["majianpeng" <majianpeng@xxxxxxxxx>]

Hi all:
	At present,I used am1808 usb-host-controler to link usb-to-serial device(using to chips all 8 serial console.)
	But I only used three console, the fourth console blocked.
	I reviewed the code and found the reason which urb bloked.
	I readed the datasheet which supporting NAKTIMEOUT for bulk transport.
	
	But the function : musb_urb_enqueue()
>>case USB_ENDPOINT_XFER_ISOC:
		/* ISO always uses logarithmic encoding */
		interval = min_t(u8, epd->bInterval, 16);
		break;
	default:
		/* REVISIT we actually want to use NAK limits, hinting to the
		 * transfer scheduling logic to try some other qh, e.g. try
		 * for 2 msec first:
		 *
		 * interval = (USB_SPEED_HIGH == urb->dev->speed) ? 16 : 2;
		 *
		 * The downside of disabling this is that transfer scheduling
		 * gets VERY unfair for nonperiodic transfers; a misbehaving
		 * peripheral could make that hurt.  That's perfectly normal
		 * for reads from network or serial adapters ... so we have
		 * partial NAKlimit support for bulk RX.
		 *
		 * The upside of disabling it is simpler transfer scheduling.
		 */
	>>	interval = 0;
	>>}
	>>qh->intv_reg = interval;
   
For bulk tran,set interval is 0,so no NAKtimeout interrupt can hanppen? Is it?
But I readed the NAKLIMINT handle:  musb_h_ep0_irq() :
>>} else if (csr & MUSB_CSR0_H_NAKTIMEOUT) {
		dev_dbg(musb->controller, "control NAK timeout\n");

		/* NOTE:  this code path would be a good place to PAUSE a
		 * control transfer, if another one is queued, so that
		 * ep0 is more likely to stay busy.  That's already done
		 * for bulk RX transfers.
		 *
		 * if (qh->ring.next != &musb->control), then
		 * we have a candidate... NAKing is *NOT* an error
		 */
>>		musb_writew(epio, MUSB_CSR0, 0);
>>		retval = IRQ_HANDLED;
	}

But did not do anything.

Is it the code error or I?
			Thanks for !
 				
--------------
majianpeng
2012-05-18

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