how to create a 512 beat loop

how i checked if the 512 beat baseline was correct... i counted 4× 128 beats before i stopped the loop recording with no sounds add-on... then I saved the clean loop on the jamman, before i overdubbed it to see if it was in order. now i onlg have to recall the clean loop and know if i start it any point can be my beginning... if its in 4×4 it will fit... long loops can be much better.