Hi,
I've got a questions for the USB gurus... What is the minimum
or typical round trip time of a USB bulk transfer ?
(BTW, I'm not on the list...)
Let's take an example...
My driver has 2 bulk pipes, in and out. The transfer is
assumed to be a single TD (typical 24 bytes) in both ways.
The timeline looks like :
t1 : USB device has data, start pushing it to host via 'in'
t2 : USB driver receives data via 'in'
t3 : USB driver has data, start pushing it to device via 'out'
t4 : USB device finished receiving data via 'out'
What I want to know is tusb = (t2-t1)+(t4-t3).
The reason : the IrDA protocol mandate what is the minimum
time between Rx and Tx on the medium, tmin. This time tmin is
negociated over the medium, and can vary from 10us to 10ms. I am
mandated to ensure that (t4-t1) > tmin. The driver can control pretty
accurately (t3-t2), and I can udelay() in the driver if needed.
Currently, I ensure that (t3-t2) > tmin. However, I strongly
suspect that tusb is in the order of 1ms for bulk transfer (due to the
USB frame beeing 1ms period). In other words, it would be pointless
for me to udelays() in the driver if tusb is larger than that...
Thanks in advance...
Jean
_______________________________________________
[EMAIL PROTECTED]
To unsubscribe, use the last form field at:
https://lists.sourceforge.net/lists/listinfo/linux-usb-devel
