The FT2232 devices actually support that much. > The usb device supports max 512 byte IN/OUT transfers in high speed mode, and it reports itself as a BULK device.Īll high-speed bulk pipes have 512 byte packets, although I'm not sure If you can figure out their packet format, you don't actually need to The driver submits URBs,Īnd the host controller worries about the scheduling. Well, not really USB doesn't work that way. > In order to improve this significant drawback, i am ready to write a KMDF usb driver, however, i am not sure if it will allow me to send and receive individual microframes in usb high speed mode. To go through their library, it might not support this. Try using overlapped I/O to submit them both at once. Library? If you are making ioctl calls to the driver directly, you can Well, but round-trips are especially painful.Īre you talking to the FTDI driver directly, or are you using their It wasn't designed for this kind of operation. So, in a very real sense, your device is simply a poor candidate for If you submit the write, then wait for that to complete,Īnd then submit the read, then the two requests cannot be handled in the Once the frame is gone, it starts scheduling the It's all scheduled in advance - the hostĬontroller driver schedules all the transfers for a frame, then submits That faster is to use overlapped I/O to submit the two requests at the So, you have to do a "write" followed by a "read"? The only way to make To have actual proper speed, the polling latency should be somewhere like 0.3ms, since the operation takes from 0.8ms to 1.6ms to actually complete. For this operation, this polling needs to be done a lot, and thus these latencies are high and limits the operation to something like 100KB/s. I am using the FTDI D2XX drivers, and the latency i get from issuing a read command to the device(a few bytes), then reading back one byte (or a bit more) is from 0.8ms-3ms according to QueryHighPerformanceCounter. > Hello i have a FT2232H based device, and so far, it's quite speedy, however, now i have a need to poll the device it's connected to, and as soon as a bit flips, continue with some action. so, could i get latency granularity less than 1ms when talking to the usb controller in KMDF mode ? The usb device supports max 512 byte IN/OUT transfers in high speed mode, and it reports itself as a BULK device. In order to improve this significant drawback, i am ready to write a KMDF usb driver, however, i am not sure if it will allow me to send and receive individual microframes in usb high speed mode. Hello i have a FT2232H based device, and so far, it's quite speedy, however, now i have a need to poll the device it's connected to, and as soon as a bit flips, continue with some action.
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