I have the following setup: FTDI USB->Serial chip hooked up to a CAN signaling transceiver. Due to the nature of CAN, I automatically get local echo back through the FTDI chip. I'm not using the CAN protocol, but just its signaling properties. The problem I am having is everytime I write something I must read back what I've written in order to read back correct data from the device it is hooked up to.
I am finding that if the string that I send is long enough (usually greater than 22 bytes in most cases), the FTDI chip splits the response into at least two IN data packets. Unfortunately there is a large delay between these two packets (for a write of 64 bytes its usually around 19ms @ 115200 baud). I'm wondering if this delay can be shortened or if it is the result of USB hardware on either end (either the FTDI chip or the USB hardware/stack on the computer side). A sample transaction with lots of debugging looks like the following: FTDI FT232BM Compatible ttyUSB0: ftdi_write - length = 64, data = 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 drivers/usb/serial/ftdi_sio.c: sent write urb, count 64, at 0us drivers/usb/serial/ftdi_sio.c: ftdi_write write returning: 64 drivers/usb/serial/ftdi_sio.c: ftdi_chars_in_buffer - port 0 drivers/usb/serial/ftdi_sio.c: ftdi_write_room - port 0 drivers/usb/serial/ftdi_sio.c: ftdi_write_bulk_callback - port 0 drivers/usb/serial/ftdi_sio.c: ftdi_chars_in_buffer - port 0 drivers/usb/serial/ftdi_sio.c: ftdi_write_room - port 0 drivers/usb/serial/ftdi_sio.c: 89: ftdi_read_bulk_callback at 2895us data_count 25 drivers/usb/serial/ftdi_sio.c: ftdi_read_bulk_callback - port 0 drivers/usb/serial/ftdi_sio.c: ftdi_process_read - port 0 FTDI FT232BM Compatible ttyUSB0: ftdi_process_read - length = 25, data = 01 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 drivers/usb/serial/ftdi_sio.c: 90: ftdi_process send urb at 2925us drivers/usb/serial/ftdi_sio.c: ftdi_chars_in_buffer - port 0 drivers/usb/serial/ftdi_sio.c: ftdi_write_room - port 0 drivers/usb/serial/ftdi_sio.c: ftdi_chars_in_buffer - port 0 drivers/usb/serial/ftdi_sio.c: ftdi_write_room - port 0 drivers/usb/serial/ftdi_sio.c: 90: ftdi_read_bulk_callback at 18893us data_count 43 drivers/usb/serial/ftdi_sio.c: ftdi_read_bulk_callback - port 0 drivers/usb/serial/ftdi_sio.c: ftdi_process_read - port 0 FTDI FT232BM Compatible ttyUSB0: ftdi_process_read - length = 43, data = 01 60 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 drivers/usb/serial/ftdi_sio.c: 91: ftdi_process send urb at 18938us drivers/usb/serial/ftdi_sio.c: ftdi_chars_in_buffer - port 0 drivers/usb/serial/ftdi_sio.c: ftdi_write_room - port 0 drivers/usb/serial/ftdi_sio.c: ftdi_close drivers/usb/serial/ftdi_sio.c: 91: ftdi_read_bulk_callback at 22891us data_count 0 drivers/usb/serial/ftdi_sio.c: ftdi_read_bulk_callback - port 0 Thanks in advance, -- James Lamanna ------------------------------------------------------- SF email is sponsored by - The IT Product Guide Read honest & candid reviews on hundreds of IT Products from real users. Discover which products truly live up to the hype. Start reading now. http://ads.osdn.com/?ad_id=6595&alloc_id=14396&op=click _______________________________________________ [email protected] To unsubscribe, use the last form field at: https://lists.sourceforge.net/lists/listinfo/linux-usb-devel
