Re: [Ftdi-usb-sio-devel] FT245BM transfer rates

[Bill R. <br...@pa...>]

Hi there,

I believe the bottleneck is how the transactions are sent to the usb 
stack. One packet at a time. The larger the writes/reads you can do the 
better - ie reduce the number of system calls. But some driver hacking 
would be required to attempt sending a bigger packet than 128bytes and 
let the usb stack split that packet up. However I don't know if the 245 
would be happy with this. It would be an interesting experiment though 
and would should give a lot more performance.

Perhaps another of the usb serial drivers has implemented a multiple 
buffer scheme to improve performance but I haven't looked at them in 
AGES so don't know.

Karl Ran wrote:

> Hi,
>
> has anyone reached transfer rates higher than this:
> write( PC to FT245 ): 58 kByte/s
> read( FT245 to PC ) : 30 kByte/s
> ?
>
> Note: The burst rate with my curent test-setup is 400 kByte/s
>
> Anyone knows where the bottleneck is?
> driver, usb-stack, ?
>
> FTDI speced the chip with 1000 kByte/s :-/
>
> Karl
>
>
>
>
>
>
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