[Qt-interest] Delay of code execution

[Jason H]

How do you know you've achieved the proper position?
Is there an ACK message that is received or interrupt that is raised?
Ideally, you'd use signal slots, and possibly a state machine. 

Let me give you and example. The elevator in my building is highly reliable and regular. But once in a while it does a double-bounce when you get to your floor (cable issue) and it doesn't open until the motion has stopped. You're guessing that a command completed ok with quickly lead to catastrophe if you assume it succeeded in the allotted time. 

However if I were confident, i would set a 200ms timer and have it read a command queue and just consume a command (channel, position) every 200ms. Then you just have to stuff 3 commands at once. 

Its been a while since I worked with GPIB, but I thought there was an OK message?





----- Original Message ----
From: Matthias Pospiech <matthias.pospiech at gmx.de>
To: Qt-interest <qt-interest at trolltech.com>
Sent: Tue, April 13, 2010 11:52:31 AM
Subject: Re: [Qt-interest] Delay of code execution

Andre Somers schrieb:
> Perhaps you should talk about the issue you want to resolve by using a 
> delay, instead of the question on how to create a delay. 
I use delay in many cases:

Here a few examples:

(1)
    piezoController->selectChannel(0);
    piezoController->setPosition(center_pos);
    delay(200);

    piezoController->selectChannel(1);
    piezoController->setPosition(center_pos);
    delay(200);

    piezoController->selectChannel(2);
    piezoController->setPosition(center_pos);
    delay(200);

The delay time may be exaggerated, but is there to ensure that the 
controller
which is connected via serial bus has finished the last command.

(2)
Here I measure the power in different positions. The RotationStage is 
connected via USB (fast),
and the AgilentPowerSensor which requires arbitrary delay times 
typically in the order of  100 ms.
Additionaly I have to wait for the Sensor to finish the last measurement.

    for (int i=0; i < iArraySize; i++)
    {  
        if(stopped) {
            break;
        }
        RotationStage->PowerOn();
        RotationStage->move(Array[i].position / 
RotationStage->CountsToDegree());      
        RotationStage->WaitForPositionReached(Array[i].position / 
RotationStage->CountsToDegree());
      
        delay(AgilentPowerSensor->AvergingTime());
        Array[i].power = AgilentPowerSensor->Power();      
    }


(3) Here a part of the GPIB communction, which is based on C-code:
The delay is required because the device requires a few 10 ms up to 
several 100 ms
time to recieve, generate and send the answer.

long GPIB_Device::GPIB_GetReply(char *command, char *response)
{
    if(ibcntl < 0) return 0;
    GPIB_Out(command);
    delay (m_GPIB_AnswerDelay);
    GPIB_In((unsigned char *)response,500);
    
response[ibcntl+1]=0;                                                    
    return ibcntl;
}

I all this cases I am talking to external devices and work with external 
libraries or communication over Serial Bus.

Hope this gives a better idea for what I require a delay.

Matthias

EDIT: Yes maybe the QxtSignalWaiter could be a solution. But 
nevertheless I would like to be sure that
all other trivial examples are not solving the problem.

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