V4 I2C cleanup opportunity: Let's add default implementations for the register methods in I2c that don't already have one

[stefanhaustein]

As far as I understand, registers are just common conventions -- they are not actually reflected in the protocol.

So we could just add default implementations, and providers wouldn't need to implement register support, reducing opportunities for unexpected differences or errors.

I am happy to create a PR to implement this if people agree that we should do this.

[eitch]

Which methods do you think are missing? But yes, always a good idea to cover the use-cases

[stefanhaustein]

I have tried to illustrate this here: #524

[stefanhaustein]

PS. Running out of forks, so here is the suggestion for the corresponding additions to I2CBase.java

   @Override
    public int readRegister(int register) {
        return execute(() -> {
            write(register);
            return read();
        });
    }Expand commentComment on line R92ResolvedCode has comments. Press enter to view.

    @Override
    public int readRegister(byte[] register, byte[] buffer, int offset, int length) {
        return writeRead(register, register.length, 0, buffer, length, offset);
    }

    @Override
    public int readRegister(int register, byte[] buffer, int offset, int length) {
        return execute(() ->{
            write(register);
            return read(buffer, offset, length);
        });
    }Expand commentComment on line R105ResolvedExpand commentComment on line R105ResolvedCode has comments. Press enter to view.

    @Override
    public int writeRegister(int register, byte b) {
        return write((byte) register, b);
    }

    @Override
    public int writeRegister(int register, byte[] data, int offset, int length) {
        Objects.checkFromIndexSize(offset, length, data.length);
        byte[] tmp = new byte[length + 1];
        tmp[0] = (byte) register;
        System.arraycopy(data, offset, tmp, 1, length);
        return write(tmp);
    }

    @Override
    public int writeRegister(byte[] register, byte[] data, int offset, int length) {
        Objects.checkFromIndexSize(offset, length, data.length);
        byte[] tmp = new byte[length + register.length];
        System.arraycopy(register,0, tmp, 0, register.length);
        System.arraycopy(data, offset, tmp, register.length, length);
        int rc = write(tmp);
        return (rc - register.length);  // do not include the register bytes as what was written...
    }

[stefanhaustein]

New plan: Back-port the code here: https://github.com/stefanhaustein/pi4j-usb-bridge/blob/a2b8caa702d1cf1dc3f4b2cd36d77b85557b816c/src/main/java/com/pi4j/usbbridge/mcp2221/I2CImpl.java#L96

(and check close / shutdown in the process)