On Tue, 22 Feb 2005 01:26:13 +1100, you wrote:

>
>Has anyone here got the FTDI 232BM chip and the VCP
>driver to transfer data downstream (PC to FTDI chip ) with a
>high efficieny  rate (95%+)  when using higher UART baud rate
>settings like 115.2k?
>
>The expected time to transfer 131072 bytes @ 115.2k baud is
>~ 11 seconds.
>
>Both the native comport and my prolific chip set based USB-RS232
>convertor transfer the full 131072 bytes in ~ 11 seconds.
>
>However the FTDI chip took ~16 seconds!  That is a ~80k bit/sec
>transfer rate or only 69% efficiency  This was using the same hub as
>the other USB-RS232 bridge.
>
>This is not an latency timer issue as the latency timer is for upstream
>transfers only.
>
>Upstream transfers are not much of an issue. I can the FTDI chip to
>send 131072 bytes upstream at a rate close to 15.2k bits/sec.
>
>However, there does seem to be an issue with the downstream transfer
>rates of the FTDI chip and the VCP driver once you go over 57600 baud.
>(57600 baud transfer was near 100% efficient.)
>
>So, has anyone found a way to get high speed downstream transfers
>using the FTDI -VCP driver combo and 115.2k baud or greater?
>
>I have two olimex MCP programmers here. One is the USB model
>the other is the older comport model. I really, really bugs me that I can
>program a 18F8722 in 16 seconds with the comport model while the USB
>model takes 21 seconds with the same firmware and baud rate...
>
>-Jim

Could you use a higher baudrate..? Delays are likely to be due to the way data is packetised for
USB, and so may be in the form of fairly constant-length gaps. 
Have you looked at the actual data timing to see if you are getting large inter-block gaps or
smaller gaps between bytes ?


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