Re: Slow data rate FT245BM to PC
- From: Hans-Bernhard Broeker <broeker@xxxxxxxxxxxxxxxxxxxxx>
- Date: 28 Aug 2005 14:08:18 GMT
zsradding.no.spam@xxxxxxxxx wrote:
> I am working on a PIC project that uses an FT245BM to transfer data to
> the PC over USB. I am transferring about 3MB of data and want to do it
> as fast as possible. However, my current solution is way too slow.
How slow exactly _is_ "way too"? Try to give some hard numbers.
Ahh... now I see you did, at the far end of your post:
> The code functions well, it is just a bit slow. It can take up to 30
> seconds to transfer 3 megs.
Well, let's see: that means you got at least 100 kByte/s, or .8 Mbit/s
of payload throughput. That's only one order of magnitude below the
baud rate. What USB transfer mode are you using?
You should also try to relate them with the bandwidth of the interface
between your PIC and the FT245BM, and the speed of the PIC itself.
> Let me start off by saying that I know VB isn't a speed demon, but I
> don't think it is the bottle neck here. I am running this on a P4
> 3.2Ghz machine, so even VB is quick.
It may feel quick, but that doesn't mean it actually is. You're
trying to talk to a low-level driver here --- there could be all kinds
of internal delays involved, not the least the context switching time
between your application and the kernel's USB layer.
> Here are the symptoms of my problem. The 245's TXE seems to go high
> (signaling that the internal buffer is full) for "long" periods of time
How long is "long"?
--
Hans-Bernhard Broeker (broeker@xxxxxxxxxxxxxxxxxxxxx)
Even if all the snow were burnt, ashes would remain.
.
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- From: zsradding . no . spam
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