From 58ea88d87a834923b31271750b8eab6403a797be Mon Sep 17 00:00:00 2001 From: Hans de Goede Date: Wed, 28 Mar 2012 20:47:51 +0200 Subject: [PATCH] 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 Signed-off-by: Gerd Hoffmann --- hw/usb/hcd-ehci.c | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-) diff --git a/hw/usb/hcd-ehci.c b/hw/usb/hcd-ehci.c index 34f7538066..be02308242 100644 --- a/hw/usb/hcd-ehci.c +++ b/hw/usb/hcd-ehci.c @@ -2149,11 +2149,15 @@ 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; }