Merge #121

121: fix critial section implementation r=dkhayes117 a=tfx2001

It should be `0b1000` rather than `0b100`. `Bit 2` is a reserved bit, and `Bit 3` is `MIE` that needs to be cleared.

![image](https://user-images.githubusercontent.com/19427212/212855746-7df197f1-5582-4844-a58e-6c7269d03b22.png

)


Co-authored-by: tfx2001 <tfx2001@outlook.com>