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How to enforce 250 millisecond delay between writes on a serial port?

Answer 1

+1 A:

Suspending the thread should work for you:

System.Threading.Thread.Sleep(250);

However, this can be a little inaccurate since you can't guarantee the next time your thread is going to be scheduled. If you need precise timings, you'd better use spin waits.

Mehrdad Afshari 2010-01-11 19:28:19

This doesn't answer the question. This would cause it to wait 250 milliseconds no matter what.

Max Schmeling 2010-01-11 19:41:49

@Max: You can use `Stopwatch` to calculate the time already passed since you wrote last time to the port and adjust the delay appropriately.

Mehrdad Afshari 2010-01-11 19:44:02

Answer 2

+2 A:

You should have some sort of class for the purpose of writing to the serial port, perhaps a single point of writing (a WriteToPort function or something).

In that, you could save the current time every time you write, then use logic on the delay for that. SO:

DateTime lastWritten;
TimeSpan timeBetweenWrites = new Timespan(0,0,0,0,250);
void WriteToDevice(string data)
{
    TimeSpan sinceLastWrite=DateTime.Now-lastWritten;
    if(sinceLastWrite<timeBetweenWrites)
        Thread.Sleep(timeBetweenWrites-sinceLastWrite);
    SerialPort.Write(data);
    lastWritten=DateTime.Now;
}

Erich 2010-01-11 19:31:51

This is what I was planning on doing. I was hoping there was some more elegant way of doing it, but I guess there probably isn't. thanks

Max Schmeling 2010-01-11 19:41:01

Alternatively, if you are willing to make your writes not necessarily 'serial' and are willing to submit them Asynchronously, you can create a thread to do the submissions that will sleep 250ms between each send, and then just wait on a lock to send in order to send.I didn't write that one up, because it is a bit more complex, and most Serial Port usage requires that the data be dealt with in a syncronous way.

Erich 2010-01-11 19:44:42

Yeah, unfortunately it needs to be done in a synchronous manner

Max Schmeling 2010-01-11 20:09:27

Variation: Have it throw an exception instead of sleeping. That way, the information is passed out instead of just automatically blocking the caller for however long. Depends on the use case into the method.

jdmichal 2010-01-11 21:03:44

Exceptions are to be used for 'exceptional' circumstances. They should not be used for program flow.

Erich 2010-01-11 21:10:53

Yes. I would consider an attempt to `WriteToDevice` at a time when writing is not permitted to be an "exceptional circumstance". As I said, it depends on the use case into the method. If it is appropriate to block the calling thread until a write can be successfully made, then the sleeping implementation is fine. But there are also use cases where blocking the thread would not be OK, in which case it would be more desirable to exception out.

jdmichal 2010-01-12 01:22:46

Answer 3

A:

Fetch a timestamp before each transmission. Sleep for the 250-(now - then) milliseconds (clamped at zero, obviously). That seems to be what you're asking for.

If, instead, you're worried about things like OS scheduling issues making times that are not 250ms on average, or more than a tiny bit off from 250ms exactly, then you have a harder problem on our hand and you will need to read up on hard real time techniques (and perhaps purchase some extra hardware).

Andy Ross 2010-01-11 19:32:41

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How to enforce 250 millisecond delay between writes on a serial port?

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