prevent bitslide from going out of range
If, for some reason, a proper alignment is missed then the cur_slide
counter
might increment outside its window (0..9 for an 8 bit Phy and 0..19 for
a 16 bit
Phy). Apparently nobody ever missed an alignment, but it might fail
someday,
somehow, sometime... Therefore it is wise to put the module function in
place.
The module function was implemented using an if statement because
synthesis
tools complained about the VHDL "mod" function.