Descriptions in SkoolKit's HTML output would be squashed together into a single long line when braces were used and a following line was omitted from the .ctl file. SkoolKit would group the braced line in another pair of braces.

Here I replace the pseudocode braces with C99 style digraphs: { and } become <% and %> to avoid the conflict.
JP P is not a parity test: it's testing the sign bit, so check A >= 128.
Improve some descriptions.
Add linux-arm-gcc target.