System.ArgumentException: Parameters 'writeBuffer' and 'readBuffer' must have the same length

[olavt]

I wrote a small test program and when running it on a Raspberry PI 3 with a PiFace Digital 2, I get the following exception:

Unhandled exception. System.ArgumentException: Parameters 'writeBuffer' and 'readBuffer' must have the same length.
at System.Device.Spi.UnixSpiDevice.TransferFullDuplex(ReadOnlySpan1 writeBuffer, Span1 readBuffer)
at Iot.Device.Mcp23xxx.Mcp23xxx.SpiAdapter.Read(Byte registerAddress, Span1 buffer) at Iot.Device.Mcp23xxx.Mcp23xxx.InternalRead(Register register, Span1 buffer, Port port)
at Iot.Device.Mcp23xxx.Mcp23xxx.InternalReadByte(Register register, Port port)
at Iot.Device.Mcp23xxx.Mcp23x1x.ReadByte(Register register, Port port)
at TestPiface.Program.Main(String[] args) in /home/vsts/work/1/s/Electronics/Implementations/TestPiface/Program.cs:line 31

The line causing the issue is:

        byte currentValue = mcp23s17.ReadByte(Register.GPIO, Port.PortA);

Shouldn't it be possible to read the state of the output ports like this?

This is the complete program:

using System;
using System.Threading.Tasks;
using System.Threading;
using Iot.Device.Mcp23xxx;
using System.Device.Spi;

namespace TestPiface
{
class Program
{
private static readonly int s_deviceAddress = 0x20;

    private static Mcp23s17 mcp23s17;

    static void Main(string[] args)
    {
        var spiConnectionSettings = new SpiConnectionSettings(0, 0)
        {
            ClockFrequency = 1000000,
            Mode = SpiMode.Mode0
        };

        var spiDevice = SpiDevice.Create(spiConnectionSettings);

        mcp23s17 = new Mcp23s17(spiDevice, s_deviceAddress);

        mcp23s17.WriteByte(Register.IODIR, 0b0000_0000, Port.PortA);    // set port A as an output
        mcp23s17.WriteByte(Register.IODIR, 0b1111_1111, Port.PortB);    // set port B as an input
        mcp23s17.WriteByte(Register.GPIO, 0b0000_0000, Port.PortA);     // Clear all outputs

        byte currentValue = mcp23s17.ReadByte(Register.GPIO, Port.PortA);

        mcp23s17.WriteByte(Register.GPIO, 0b0000_0010, Port.PortA);
    }

}

}

[krwq]

cc: @shaggygi

[shaggygi]

@krwq I honestly have not used this device with the new BusAdapter scheme.

I'm thinking it blows up in this method call as the buffer sizes are updated before calling TransferFullDuplex.

Briefly reviewing the code, it looks like the buffer is set to a size of 1 before calling the Read method. writeBuffer is set to a size of 2 with GetOpCode and registerAddress (line 42). readBuffer is set to a size of 3 on line 48).

[krwq]

thanks, no problem @shaggygi I'll see if I have some time to take a look at this (I think I have this expander lying around somewhere)

[gsutra]

Hi,

We are facing the same issue. @krwq Would you have a quick workaround ?

[joperezr]

@gsutra do you mind sharing the callstack and if possible your sample repro code as well so we can investigate and either fix the issue or give you a workaround?

[lpayet]

Hi,
I'm working with @gsutra.

Here is the code :
`
using Iot.Device.Mcp23xxx;
using System;
using System.Device.Gpio;
using System.Device.Spi;

namespace Test
{
public class Program
{
public static void Main(string[] args)
{
var spiConnectionSettings = new SpiConnectionSettings(2, 1)
{
ClockFrequency = 1000000,
Mode = SpiMode.Mode0
};
SpiDevice spiDevice = SpiDevice.Create(spiConnectionSettings);

        Mcp23s17 mcp23S17 = new Mcp23s17(spiDevice, 0x20);

        byte result = mcp23S17.ReadByte(Register.GPIO, Port.PortA);
        Console.WriteLine(result);
    }
}

}
`

And the callstack :

Unhandled exception. System.ArgumentException: Parameters 'writeBuffer' and 'readBuffer' must have the same length.
at System.Device.Spi.UnixSpiDevice.TransferFullDuplex(ReadOnlySpan1 writeBuffer, Span1 readBuffer)
at Iot.Device.Mcp23xxx.Mcp23xxx.SpiAdapter.Read(Byte registerAddress, Span1 buffer) at Iot.Device.Mcp23xxx.Mcp23xxx.InternalRead(Register register, Span1 buffer, Port port)
at Iot.Device.Mcp23xxx.Mcp23xxx.InternalReadByte(Register register, Port port)
at Iot.Device.Mcp23xxx.Mcp23x1x.ReadByte(Register register, Port port)
at Test.Program.Main(String[] args) in Test\Program.cs:line 21
Abandon

[fennixsystems]

Was a solution ever found to this issue? I'm experiencing it with the latest build and very similar/basic test code.

[shaggygi]

@fennixsystems I still believe the error is within my comment above, but don't believe there was a fix yet.

[fennixsystems]

@shaggygi Any idea when there might be a fix? Or even a fix I can implement myself temporarily?

[SaDiablo]

This might be caused by improper usage of transfer full duplex in Mcp23xxx\SpiAdapter.cs

public override void Read(byte registerAddress, Span<byte> buffer)
{
    // Include OpCode and Register Address.
    Span<byte> writeBuffer = stackalloc byte[]
    {
        GetOpCode(_deviceAddress, isReadCommand: true),
        registerAddress
    };

    Span<byte> readBuffer = stackalloc byte[buffer.Length + 2];

    // Should this also contain the op code and register?
    // Why are we transferring full duplex if we only really
    // need to read?
    _device.TransferFullDuplex(writeBuffer, readBuffer);

    // First 2 bytes are from sending OpCode and Register Address.
    readBuffer.Slice(2).CopyTo(buffer);
}

^ If you are able you might check what sizes are readBuffer and writeBuffer in your case and try to see what's going on. (this might help you debug your RPi code remotely: Debugging Your .Net Core 3 App on Your Raspberry Pi with Visual Studio 2019)

As a one way to you can try to fix it is to use software version of spi, because this exact error is impossible to occur (error in the code shown below) but it probably won't work in further steps or cause more bugs

SoftwareSpi.cs

if (dataToRead.Length != dataToRead.Length)
{
    throw new ArgumentException(nameof(dataToWrite));
}

whereas Unix and Windows spi Devices

if (writeBuffer.Length != readBuffer.Length)
{
    throw new ArgumentException($"Parameters '{nameof(writeBuffer)}' and '{nameof(readBuffer)}' must have the same length.");
}

so that's something to take note of.

Hope that helps you at least a bit