devf-generic, the -s option

Hello. In the documentation for devf-generic the ‘-s’ is shown as:
-s base[,w_size[,a_offset[,a_size[,u_size]]]]
but I cannot find a good description of all these 'sub’parameters. base and
w_size are quite obviuos but the rest.

Does anyone know the meaning of these?

regards, Mats P