libftdi Archives

Subject: Re: FT245R transfer rates

From: Xiaofan Chen <xiaofanc@xxxxxxxxx>
To: libftdi@xxxxxxxxxxxxxxxxxxxxxxx
Date: Mon, 22 Feb 2010 22:46:50 +0800
On Mon, Feb 22, 2010 at 10:39 PM, Jan Wilmans <janwilmans@xxxxxxxxx> wrote:
> Yes, I understand, but to actually be able to receive 9 full buffers, the
> hardware reading from the FT245 must
> read the data faster (or at least as fast) then it is arriving over USB,
> otherwise the buffer will be full and no more data can be received.

That is right.

> My assumption was, and I see how I was wrong about that now, that the
> hardware would never be reading that fast. And so I assumed that there
> could never arrive more then one buffersize of data per millisecond.

It all depends on the FIFO engine (or CPUs for other USB MCUs).

Here are some good explanations of USB transfer throughput
by Tsuneo, a real USB experts. Read his posts in the full thread as well
to understand how the host and driver play a part as well.


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