Endianess for ModbusTcpServer

I have seen that the ModbusTcpServer checks if we have Little or Big-Endian. My system (Linux ARM32) is Little-Endian. When I check the data (with ModbusPoll) - it is not reversed.

For example:

Span<short> inputreg = server.GetInputRegisterBuffer<short>();
inputreg[0] = 1;

In ModbusPoll I got “256” (0x0100), I expected “1” (0x0001). It was possible that I manually reverse my data before with ModbusUtils.SwitchEndianness(), but I was wondering if there is a cleaner solution for it.

With the client I was able to receive the data in the correct endianess:

client.Connect(IPAddress.Parse("1.2.3.4"), ModbusEndianness.BigEndian);

It would be great if someone could help me, or tell me if it makes sense to reverse every single value before.

[Apollo3zehn]

Yes the content is returned without changes. The check in the extension method will be lightweight, so you should not notice any performance impact.

Start offset: If you set the 8 byte double value to buffer[1], it would be located at byte positions 8-15 which is equal to Modbus registers 4-7 (with 2 bytes per Modbus register). But if you want to have it located at Modbus registers 1-5, you need a way to specify a start offset (in bytes).

Since everything is clear for me now, I will prepare a draft and hopefully finish it on Monday.

[mkroesen]

Sounds good, I think this is a good solution. Thanks a lot!