libftdi Archives

Subject: Re: Latency timer of zero should be allowed on FTxxxxH devices.

From: Thomas Jarosch <thomas.jarosch@xxxxxxxxxxxxx>
To: libftdi@xxxxxxxxxxxxxxxxxxxxxxx
Cc: Uwe Bonnes <bon@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx>
Date: Fri, 23 Feb 2018 09:23:45 +0100
Good morning Uwe,

On Thursday, 22 February 2018 10:29:32 CET Uwe Bonnes wrote:
> Hello,
> 
> I want to bring up an old report from  19 Aug 2010.
> 
> The issue seems not to be resolved yet:
> >>>>> "Fewell," == Fewell, Edward <efewell@xxxxxx> writes:
>     Fewell,> Per Gordon Lunn of FTDI: "With the FTxxxxH devices a latency of
> Fewell,> 0ms actually works and allows for fastest performance."
> 
>     Fewell,> I confirmed with a modified libftdi driver that this does work
>     Fewell,> with a FT2232H chip, and can improve throughput.
> 
>     Fewell,> Edward Fewell
> 
> This will help with small transactions.

we could add a special case for the FT2232H chips,
that would be easy to do.

When I see code like this in the library

if (ftdi->type == TYPE_2232H || ftdi->type == TYPE_4232H || ftdi->type == 
TYPE_232H)
    packet_size = 512;


I'm wondering if the other hi-speed xxxH devices also support this?

Cheers,
Thomas




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