\>>>>> "Alan" == Alan Stern <[EMAIL PROTECTED]> writes:
Alan> On Sun, 13 Feb 2005, Uwe Bonnes wrote:
...
Alan> Now I understand your question.
Alan> The rate at which control messages are sent to the bus depends on
Alan> factors other than the controller speed. It's possible for a
Alan> driver or program to "queue" messages (submit more than one
Alan> without waiting for the first one to complete). Queued messages
Alan> are sent to the bus about as fast as possible: Each is sent as
Alan> soon as the acknowledgment for the previous one is received,
Alan> without regard to 1 kHz or 8 kHz frame boundaries.
Alan> However completion of messages is reported to drivers only at a
Alan> frame or micro-frame boundary. If a driver or program waits for
Alan> the first message to complete before submitting the second, then
Alan> the behavior you observed would result.
Alan,
thanks for you time. We are close now, but still the main answer is
touched NYET :-)
The bitbanging happens with controlmessages sent via libusb, like:
usb_control_msg(ftdi->usb_dev, 0xC0, 0x0C, 0, ftdi->index, (char *)&usb_val,
1, ftdi->usb_read_timeout)
With these control messages, the pins effectivly change state at 125 /1000
us steps. The scope clearly tells that. So it seems that control messages
are not queued, at least not sent that way via libusb/usbdevfs.
But my original question: Why does pin state changes caused by sending of
control messages happen at 1000 us intervals when the USB2.0 full speed
device is connected direct to the PC, while it happens 8 times faster at 125
us intervalls, when a USB 2.0 hub is connected in between PC and device.
I think this is a missbehaviour of our USB stack...
Bye
--
Uwe Bonnes [EMAIL PROTECTED]
Institut fuer Kernphysik Schlossgartenstrasse 9 64289 Darmstadt
--------- Tel. 06151 162516 -------- Fax. 06151 164321 ----------
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