Requests following a rejected SETUP requests failed too, which sometimes

produces user-visible errors and may confuse implementations. (E.g., when
probing for an unimplemented feature and subsequently being greeted by a
timeout.)

- fw/comon/usb.c (handle_setup): set SOPRDY when answering a request error
  with a stall, according to the example in AN139. This seems to eliminate
  the timeouts observed in requests following after bad requests.
- fw/boot/boot.c (run_payload): described how the host is expected to
  respond to the device resetting its USB stack

fw/boot/boot.c

@@ -71,6 +71,15 @@ void run_payload(void)
 	/* Restart USB */
 	USB0XCN = 0;
 
+	/*
+	 * The USB host must detect a disconnect (pull-ups absent) within 2 and
+	 * 2.5 us according to parameter Tddis in table 7-13 on page 186 of the
+	 * Universal Serial Bus Specification Revision 2.0.
+	 *
+	 * If our application calls usb_init really really quickly, we may need
+	 * an extra delay here.
+	 */
+
 	debug("launching payload\n");
 
 	__asm

fw/common/usb.c

@@ -1,8 +1,8 @@
 /*
  * common/usb.c - USB hardware setup and standard device requests
  *
- * Written 2008, 2009 by Werner Almesberger
- * Copyright 2008m 2009 Werner Almesberger
+ * Written 2008-2010 by Werner Almesberger
+ * Copyright 2008-2010 Werner Almesberger
  *
  * This program is free software; you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -258,8 +258,9 @@ okay:
 	}
 stall:
 	printk("STALL\n");
-	usb_write(E0CSR, SDSTL_0);
-	ep0.state = EP_STALL;
+	/* AN139 recommends this sequence */
+	usb_write(E0CSR, SOPRDY | SDSTL_0);
+	ep0.state = EP_IDLE;
 }