G-code commands to rotate the A-axis by 90 degree?

I have a rotary installed. I would like to execute a four-sided Job.

I would use the regular post processor to cut the first side, a regular XYZ carve.
Then I would like to rotate the piece by 90 or 180 degrees.

To do that I would install the rotary processor, and swap the Y for the A cables.

What are the G-code commands to tell the A-axis to rotate by 90 or 180 degrees?