Ports and Interfaces > USB

Bulk transaction fails on some devices.

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Jonatan44:
Hi,
I've developed a EHCI driver working with full-speed devices.
Bulk transactions work for some devices, but for other the transactions fails (QTD status is 0x42).
it's impotent to note that the configuration process is positive for all devices, means get device descriptor, get configuration, etc, are working well.
all the devices are connected through usb 2.0 hub.

my usb tracer shown that a turn-around error occurred, I've checked the specification for this kind of issue and understood that it's happening because the delay between every package the HC submit to the device is the small.
I've tried to change the micro-frame rate (by default it's set to 8 micro-frame) but with no success.
could it be related to the fact that I'm working with a usb 2.0 hub?

Thanks,
Jonatan.

Jan Axelson:
The hub adds the complication that the host must use split transactions to access the device so you might look at where the error is occurring in relation to that.

Jan

Jonatan44:
Hi Jan,
my driver does uses split transactions, as i noted it is working for some devices (from the same class, speed, etc..)
the turnaround error occurs on the first bulk transaction, do you have any hint about what parameters do i need to change in my driver? do you think it's related to the TT buffer?

thanks!

Jan Axelson:
7.1.18.2 in the USB spec defines inter-packet delays and turnaround times. The minimum high-speed turnaround time is 8 bit widths. Are you sure that is the problem? Which transaction (Start Split, Complete Split) does the error occur in?

Jan

Jonatan44:
Hi Jan
There is only one transaction (Start Split) for now.
as i sad he transaction works for some devices (from the same manufacture)  but for others it just doesn't work.
my USB Tracer shows that there is a turn-around problem for the transaction, I did try to program FLADJ register to every combination but it's seems that it don't solve the problem.
im pretty sure it's really a turn-around problem, i'm just not sure were is the next place to try fixing the problem.

hope you could help me.
Jonatan.

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