On Mon, 25 Sep 2006, Vivek Dharmadhikari wrote:
> > The driver _did_ enqueue commands after the timeout errors.
>
> Got it ! The USB analyzer indicates that same CBW was repeated three
> times in row because the device did not generate ACK for the CBW. After
> three failed attempts, usb_stor_Bulk_reset is invoked. Is there a way to
> increase the retry count from its current value of 3 ?
Not easily. The retry count is limited in the hardware to 3, or it can be
disabled so that you get unlimited retries. Maybe this would help you, I
don't know. In my experience when a device fails to send an ACK or a NAK
in response to a packet, more retries don't help -- the device usually
needs to be reset. But perhaps your case is different.
The patch for unlimited retries is below. Note this patch is for 2.6.18;
it may need some adjusting to apply to your old kernel.
> Note also that when the same key attached to a linux PC, successfully
> generates ACK for all the CBW.
This indicates that the problem is a small hardware incompatibility, as I
have said before. For whatever reason, sometimes the device isn't able to
understand the signals coming from the computer. Maybe the embedded
device (or something near it) puts out just a little too much
electromagnetic interference.
Alan Stern
Index: mm/drivers/usb/host/ohci-q.c
===================================================================
--- mm.orig/drivers/usb/host/ohci-q.c
+++ mm/drivers/usb/host/ohci-q.c
@@ -625,8 +625,8 @@ static void td_submit_urb (
/* FALLTHROUGH */
case PIPE_BULK:
info = is_out
- ? TD_T_TOGGLE | TD_CC | TD_DP_OUT
- : TD_T_TOGGLE | TD_CC | TD_DP_IN;
+ ? TD_T_TOGGLE | TD_CC | TD_DP_OUT | TD_EC
+ : TD_T_TOGGLE | TD_CC | TD_DP_IN | TD_EC;
/* TDs _could_ transfer up to 8K each */
while (data_len > 4096) {
td_fill (ohci, info, data, 4096, urb, cnt);
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