From 9d604ddc4770f8f25de148e9b35687817a5d4110 Mon Sep 17 00:00:00 2001

From: Hans de Goede <hdegoede@redhat.com>

Date: Wed, 28 Mar 2012 20:31:32 +0200

Subject: [PATCH 141/146] usb-ehci: frindex always is a 14 bits counter

frindex always is a 14 bits counter, and not a 13 bits one as we were

emulating. There are some subtle hints to this in the spec, first of all

"Table 2-12. FRINDEX - Frame Index Register" says:

"Bit 13:0 Frame Index. The value in this register increments at the end of

each time frame (e.g. micro-frame). Bits [N:3] are used for the Frame List

current index. This means that each location of the frame list is accessed

8 times (frames or micro-frames) before moving to the next index. The

following illustrates values of N based on the value of the Frame List

Size field in the USBCMD register.

USBCMD[Frame List Size]	Number Elements		 N

00b				1024		12

01b				 512		11

10b				 256		10

11b			    Reserved"

Notice how the text talks about "Bits [N:3]" are used ..., it does

NOT say that when N == 12 (our case) the counter will wrap from 8191 to 0,

or in otherwords that it is a 13 bits counter (bits 0 - 12).

The other hint is in "Table 2-10. USBSTS USB Status Register Bit Definitions":

"Bit 3 Frame List Rollover - R/WC. The Host Controller sets this bit to a one

when the Frame List Index (see Section 2.3.4) rolls over from its maximum value

to zero. The exact value at which the rollover occurs depends on the frame

list size. For example, if the frame list size (as programmed in the Frame

List Size field of the USBCMD register) is 1024, the Frame Index Register

rolls over every time FRINDEX[13] toggles. Similarly, if the size is 512,

the Host Controller sets this bit to a one every time FRINDEX[12] toggles."

Notice how this text talks about setting bit 3 when bit 13 of frindex toggles

(when there are 1024 entries, so our case), so this indicates that frindex

has a bit 13 making it a 14 bit counter.

Besides these clear hints the real proof is in the pudding. Before this

patch I could not stream data from a USB2 webcam under Windows XP, after

this cam using a USB2 webcam under Windows XP works fine, and no regressions

with other operating systems were seen.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>

---

 hw/usb-ehci.c |    8 ++++++--

 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/hw/usb-ehci.c b/hw/usb-ehci.c

index b5d7037..3934bf0 100644

--- a/hw/usb-ehci.c

+++ b/hw/usb-ehci.c

@@ -2157,11 +2157,15 @@ static void ehci_frame_timer(void *opaque)

         if ( !(ehci->usbsts & USBSTS_HALT)) {

             ehci->frindex += 8;

-            if (ehci->frindex > 0x00001fff) {

-                ehci->frindex = 0;

+            if (ehci->frindex == 0x00002000) {

                 ehci_set_interrupt(ehci, USBSTS_FLR);

             }

+            if (ehci->frindex == 0x00004000) {

+                ehci_set_interrupt(ehci, USBSTS_FLR);

+                ehci->frindex = 0;

+            }

+

             ehci->sofv = (ehci->frindex - 1) >> 3;

             ehci->sofv &= 0x000003ff;

         }

-- 

1.7.9.3