'real time' issues

[Leisha Wharfield]

Thank you, Paul. I checked out the link you sent me. My serial device is 
not a box at all--it's two buttons designed for people who have physical 
limitations. They are about 2-1/2" in diameter and very easy to press, 
resulting in a clear audible click. There's no box at all: the buttons 
are wired into a serial connector that I bought at Radio Shack. The 
buttons are configured as a port device where the left button returns a 
5 and the right button returns a 6.

Does this sound similar to how the PST Serial Response Box works?

Your advice has been extremely helpful. I will be able to answer all the 
technical questions that are thrown at me about this purchase when the 
time comes & make my recommendation with more confidence, thanks to you.

Sincerely,

Leisha

Paul Gr wrote:

> Hi Leisha,
>
> The serial port is fine. Although in most cases the parallel printer 
> port and the game port are also usable. This is the case when the 
> buttons are connected 'directly' to the input lines of the port (not 
> the serial Rx/Tx transmission lines) and a 'Port' device is used in 
> EPrime to scan the corresponding IO register. (See also 
> http://www.psy.vu.nl/download/menu/index.html)
>
> Note that the PST Serial Response Box uses a different technique to 
> send the button states to the serial port. In this case a sequence of 
> bytes is transferred to the Rx line of the serial port. It is not very 
> likely that your button box uses this serial protocol because it 
> requires additional electronics and software.
>
> best,
> paul
>
>
>
>> From: Leisha Wharfield <leisha at decisionresearch.org>
>> To: Paul Gr <pauls_postbus at hotmail.com>
>> CC: eprime at mail.talkbank.org
>> Subject: Re: 'real time' issues
>> Date: Fri, 06 Jan 2006 17:32:23 -0800
>>
>> So your advice is to stick with the serial port? Thanks for the 
>> wikipedia link.
>>
>> Leisha
>>
>> Paul Gr wrote:
>>
>>>
>>> hello Leisha,
>>>
>>> A small note on ‘real time’ issues:
>>>
>>> Since marketing people like to use ‘sexy’ words to promote 
>>> additional functionality or suggest superior specifications, we have 
>>> to be a bit careful how to interpret the words ‘real time’ 
>>> correctly. The actual meaning depends on the context: Most hardware 
>>> and software engineers use the words ‘real time’ to indicate that 
>>> the time allowed to execute some kind of operation is limited to a 
>>> known maximum. Some engineers also differentiate between so called 
>>> hard and soft real time. In hard real time systems it is an absolute 
>>> system failure if the real time criteria are not met. (Ie. the air 
>>> bag in a car is definitely a hard real time system.) In soft real 
>>> time systems the real time criteria are less strict. This is the 
>>> case with EPrime where it is sufficient to keep track of such timing 
>>> failures. (See also http://en.wikipedia.org/wiki/Real_time) Anyway, 
>>> this kind of real time is about the response time limits of a 
>>> system, not its execution speed or bandwidth.
>>>
>>> Real time streaming media protocols on the other hand, are said to 
>>> play media in ‘real time’ when it is possible to play the media 
>>> stream at the correct speed (ie. not in slow motion.) So, in this 
>>> case marketing people and engineers refer to the large bandwidth or 
>>> execution speed of the system, not maximum response latency. In 
>>> other words: even though Firewire and USB standards support large 
>>> bandwidths, this does not mean that they support short (<1ms) 
>>> transmission delays. Furthermore, the complex protocol stacks that 
>>> are used to implement those communication systems make it almost 
>>> impossible to realize short latencies. But even if you are willing 
>>> to accept timing errors, it is not very trivial to develop hardware 
>>> that connects through USB or Firewire. RS232 and parallel ports are 
>>> much easier to use in both hard- and software.
>>>
>>> There are some real time systems that use another common connection 
>>> between de external hardware and the computer: Ethernet. A 
>>> (dedicated) Ethernet connection supports high bandwidth and short 
>>> transmission latencies. However, as with USB and Firewire, it is not 
>>> very easy to develop hard- and software for such a connection. (Note 
>>> that PST writes it will support some kind of Network Socket Device 
>>> in version 2.)
>>>
>>> Paul Groot
>>>
>>>
>>>
>>>> From: Leisha Wharfield <leisha at decisionresearch.org>
>>>> To: Alison Wright <alison.wright at kcl.ac.uk>, 'E-Prime' 
>>>> <eprime at mail.talkbank.org>
>>>> Subject: Laptop replies + new issue #5
>>>> Date: Thu, 05 Jan 2006 10:33:00 -0800
>>>>
>>> ...
>>>
>>>>
>>>> 5. A final issue to add: We use input devices that were made for 
>>>> our RT experiments. They are large switches or buttons, one for 
>>>> each hand, that can be pushed easily and give a solid clicking 
>>>> sound. They are wired into a serial device because when we began 
>>>> this series of RT computer experiments, we were told that the 
>>>> serial port was the cleanest, quickest way to get to the processor 
>>>> and we are measuring very fine time differences. Now serial ports 
>>>> are hard to come by on laptops, and when I read about new laptop 
>>>> connectors I find that the now-standard FireWire IEEE 1394 is a 
>>>> port that was designed for using a computer in "real time," that 
>>>> is, to play 3D games or to interact with streaming video. Wouldn't 
>>>> this now be the best port for measuring very fine time differences? 
>>>> Or is serial still the best way to go?
>>>>
>>>> I'll post another synopsis of replies received.
>>>>
>>>> Thanks for all your help.
>>>>
>>>> Leisha
>>>>
>>>
>>>
>>>
>>
>> -- 
>> "Billions and billions."
>>
>> And it wasn't written, it appeared spontaneously with a big bang.
>> And God said, "Let them eat archaic."
>> And God looked on it, and said, "MMMmmmmmm... /sprinkles/!"
>>
>> Dennis M. Hammes
>>
>>
>
>
>
>

-- 
"Billions and billions."

   And it wasn't written, it appeared spontaneously with a big bang.
   And God said, "Let them eat archaic."
   And God looked on it, and said, "MMMmmmmmm... /sprinkles/!" 

   Dennis M. Hammes