The DcrOut and _DcrIn DCR routines read and write incorrect values from the registers.
To work around this issue, change the optimization level for the drivers as follows:
1. Inside of XPS, select Project from the pull-down menu.
2. Select Software Platform Settings.
3. Bring the middle tab forward.
4. In the extra_compiler_flags entry, insert "-g -O0".
A fix for this problem is included in EDK 8.1i service pack 1.