Fix issue #109, SPI needs to read register SPI_USER(SPI_NO) instead o…

[mtavenrath]

…f using the value SPI_USER(SPI_NO) as base value for SPI_USER in SPI::transfer and SPI::transfer32

[mtavenrath]

@harry-boe Can you check if this fix also works with the SDCard library?

I think this fix is better than initializing mySettings._user_regvalue with the value of mySettings._user_regvalue = SPI_USER(SPI_NO);

The alternate fix I haven't tried yet would be reading the register SPI_USER(SPI_NO) instead of using the value SPI_USER(SPI_NO) though I don't see why this is more useful unless we want to restore the original value in endTransaction.

[harry-boe]

It might work that way but it will break wit the idea to preserve the register for multiple SPI clients with different Settings (i.e. Register Values)

[mtavenrath]

The code now preserves the user register in beginTransaction and restores it in endTransaction.

[harry-boe]

From the logic side this should work as well.
Unfortunately i have no time for testing. Did you tested that case with multiple devices ?