Re: [Ftdi-usb-sio-devel] latency on serial port

[BillRebey <Bi...@Re...>]

jintao,

I'm watching this thread with great interest.  

If you happen to solve the problem outside the context of this thread, thus
"obscuring " the solution from the rest of us, would you be so kind as to
document your findings here and post the solution for the rest of us?

Thanks!

Bill Rebey  (Not to be confused with Bill Ryder - the other poster)


-----Original Message-----
From: Tao Jin [mailto:jin...@gm...] 
Sent: Wednesday, June 23, 2010 1:36 AM
To: Bill Ryder
Cc: ftd...@li...
Subject: Re: [Ftdi-usb-sio-devel] latency on serial port

Hi Bill,

Thanks a lot for your quick response!  I set VMIN=1, VTIME=0 so the
serial device works in block mode.

I just tried the serial echo test on my linksys linux router, which
has onboard serial port.  setserial works for me and the RTT latency
can be reduced down to below 1ms

But when I did the same test on my laptop with a FT232RL usb-to-serial
adapter, the setserial doesn't work.   Probably the usb serial device
works in different way?  Sorry I am new to Linux kernel

Thanks again!

jintao

On Wed, Jun 23, 2010 at 1:14 AM, Bill Ryder <bil...@gm...> wrote:
> Have a look at this:
>
> http://www.tldp.org/HOWTO/Serial-Programming-HOWTO/index.html
>
> You are probably setup to do 0.1s timeout when reading the port which is
the
> default.
>
> you need to set  VMIN/VTIME properly.
>
>
>
>
> On Wed, Jun 23, 2010 at 4:57 PM, Tao Jin <jin...@gm...> wrote:
>>
>> Dear all,http://www.tldp.org/HOWTO/Serial-Programming-HOWTO/index.html
>>
>> I am trying to get my laptop running Ubuntu to communicate with a
>> sensor through serial interface.  I used usb-to-serial adapter to
>> connect the laptop and sensor serial RX/TX pins.  I observed a long
>> latency when I do a one-byte serial echo test, around 10ms.
>>
>> I googled a bit, and seems a lot of people had the same issue. someone
>> said setserial /dev/ttyS* low_latency can get the serial device work
>> in low latency mode, with higher CPU load.  I tried, that doesn't work
>> for me.
>>
>> Anyone here know about this latency issue on serial link?  Could you
>> please provide some guidance to resolve this issue?
>>
>> Thanks a lot in advance!
>>
>> jintao
>>
>>
>>
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>

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