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Subject: Re: FT245R transfer rates

From: Jan Wilmans <janwilmans@xxxxxxxxx>
To: libftdi@xxxxxxxxxxxxxxxxxxxxxxx
Date: Mon, 22 Feb 2010 14:02:09 +0100

thanks for your reply,

can have multiple packets (up to 64Bytes for full speed bulk endpoint)
per transfer, actually up to 19 for full speed USB. So the theoretically
the maximum transfer rate for full speed USB bulk transfer is
19x64=1216 Bytes/ms.

FT245R's receive buffer is double the max packet size (64x2=128) and
the transmit buffer is quad the max packet size (64x4=256). So it can
approach the maximum transfer rate limit of Full Speed Bulk Endpoint.
The driver of course need to be able to sustaining the data rate. So
FTDI has its own driver and not use Windows' lousy usbser.sys driver.

Basically what you are saying is that in the: "Data transfer rates up to 1Mbyte / second."
what they mean is 125Kb/s downspeed (host -> FT245 data transfer) and 250Kb/s upspeed (FT245 -> host data transfer) = ~~ 1Mb/s (actually 750 Kb/s) ??

So you agree that when looking at the speed of data in one direction only (host -> FT245R transfers) the
speeds is indeed only 125 Kb/s ?

Or am I mis-interpreting?


Jan Wilmans

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