I have finally got my hands on some embedded FTDI hardware (the 245 FIFO device attached to a microcontroller) and have it attached to my PC.
I have written a simple Windows application on the PC that transmits a 128 byte block of data to the embedded controller, using the FTD2xx DLL.
The embedded controller is sat in a tight loop interrogating the FTDI device, reading the 128 byte block, bitwise inverting it and sending it back to the PC.
The application records the PC time immediately (via Now()) before the transmission and the time as soon as it detects that it has 128 bytes in the receive buffer.
The check for data happens in a timer event, running every millisecond.
So finally I get around to a question...
This "round trip" of the data appears to take normally 10 milliseconds, and sometime 20 and I don't appear to be able to influence this time.
There is definitely SOMETHING that is happening with a 10 millisecond granularity.
I have tried playing with the latency timer - changing it between 1 and 255 milliseconds, but no effect at all.
Does this ring any bells with the folks that have had experience with these FTDI devices?
I can probably live with this throughput if that is what I get, but I could do with better if it is do-able.
Thanks in advance,