ReadI2CByte is Slow

[Christophe06410]

Hello,
I am trying to read impulsions from input on AB Electronics IO PI Plus card.
Using ReadPort can take up to 45 milli seconds.
I need 2 ms to be able to count impulsions (this is coming from a liquid volume reader (debitmeter)).

I am trying on both rapsberry pi and bananapi. It seems a bit better on raspberry, but not much (up to 30 ms).

Is it faster to read pins one by one instead of ports as a whole?

Here are some extracts of my code (note I mved out some variables to reduce Garbage Collect in an attempt to improve performances):
List baps = new List();
private byte[] byteArrayReturnValue = new byte[1];

        // Init busses and ports:
        baps.Add(new BusAndPort() { IOPi = Iopi20, Port = 1 });
        baps.Add(new BusAndPort() { IOPi = Iopi21, Port = 0 });
        baps.Add(new BusAndPort() { IOPi = Iopi21, Port = 1 });

        foreach (BusAndPort busAndPort in baps)
        {
            busAndPort.IOPi?.ReadPortWithoutNew(busAndPort.Port, byteArrayReturnValue);
            busAndPort.LastValue = byteArrayReturnValue[0];
        }

    public void ReadPortWithoutNew(byte port, byte[] returnValue)
    {
        CheckConnected();

        switch (port)
        {
            case 0:
                helper.ReadI2CByteWithoutNew(i2cbus, GPIOAArray, returnValue);
                return;
            case 1:
                helper.ReadI2CByteWithoutNew(i2cbus, GPIOBArray, returnValue);
                return;
            default:
                throw new ArgumentOutOfRangeException(nameof(port));
        }
    }

	internal void ReadI2CByteWithoutNew(I2cDevice bus, byte[] register, byte[] returnValue)
	{
		bus.WriteRead(register, returnValue);
	}

Thank you

[abelectronicsuk]

Hello

It is faster to read a port instead of reading individual pins. When reading a pin from the IO Pi bus, you have to read the whole port as a single 8-bit byte and then get the pin value from one of the bits in that byte. Reading all the pins on a port one by one could be over 8 times slower than reading the port as a whole.

You should be able to increase the sample rate by increasing the clock rate on the I2C bus. The default rate on the Raspberry Pi usually is 100Khz, but the IO Pi Plus will work up to 800KHz, so by changing the bus speed to 800KHz, you should see a performance improvement.

[Christophe06410]

Hi,

Thank you, I will try this.
Have a nice day.