Arduino Mega 2650 + Matlab/Simulink - Serial decimation

Question

I am performing a control analysis on an Arduino board.
As such, I want to minimize the board cycle duration.
(Faster board = faster controller).

Introduction:

I use Mathworks Matlab/Simulink to program the board.
I created a model in Simulink,
and embedded this model into my Arduino Mega 2650.

The model includes an Arduino Serial Transmit block.
I am therefore able to use Matlab software on my PC to request
serial transmission from the Arduino board to Matlab.

The Arduino Mega 2650 has the following serial constraints:

Maximum output buffer: 64 [byte]
Maximum baud frequency: ~115,000 [bit/s]

Problem:

To perform my control analysis,
I want to minimize the board cycle duration, and
I want to read several signals simultaneously.

The time it takes to read all signals sent
(as dictated by the baud rate)
is the primary obstacle in reducing my board cycle duration.

Requested Information:

Is it possible to reduce the board cycle duration
without reducing the duration in which
the serial transmission must be completed.

For example,
what if I run my board at 0.001 [s],
but I can only send all of my signals in 0.010 [s], what will happen during my reads?

If I read every 0.001 [s], obviously I will not receive all of the data,
as this is not feasible in the time that I am allotting.
My concern is regarding what will happen if I read every 0.010 [s]:

Will the passing of several board cycles before the read completes affect the read?
Is there a method to lock the serial output buffer while reading
(such that the data does not change midread)?
How long does it typically take to refill the serial output buffer with the next set of data?

Conclusion:

Ultimately, I would like to run the board as fast as possible,
since I believe that this could significantly improve my controller's performance,
despite not being able to read these additional cycles.

score 1 · Answer 1 · answered May 30 '17 at 18:36

I don't think there will be a problem in this.

I do not understand exactly why you can only send signals every 0.010 s.

The board runs at 16 MHz, that's 16 million cycles per second, however, every 'instruction' normally takes many cycles (let along parsed C/Arduino language).

What you can do is to copy the read information into an array and use it later.

Keep in mind that the serial buffer is 64 bytes. If more is read, data will be overwritten. However, if you copy the buffer into your own (larger) buffer it might help. Also you can change the 64 bytes (it's somewhere in the Serial library).

The buffer works (afaik) with a sort of circular buffer, meaning it can store 64 bytes maximum 'unprocessed' bytes. So you don't have to wait until the buffer is full before processing (actually, this is not even the best method). You can process it as long as there are bytes available.

The pseudo code can be as follows:

lastSignalSent = millis(); // last time signals sent

void loop()
{
    while serial bytes available
    {
        process bytes
    }

    if (millis() - lastSignalSent > 10) // More than 10 ms ago
    {
        Send signals
         lastSignalSent = millis();
    }
}

This assumes the serial byte processing can be done faster than they arrive, but if not, you run into problems anyway, since the serial buffer (of only 64 bytes) will be full too fast.

Arduino Mega 2650 + Matlab/Simulink - Serial decimation

Introduction:

Problem:

Requested Information:

Conclusion:

1 Answers1