> Jason> Hmm ... I can't seem to find this constant...though, I remember
> Jason> a discussion about it...
> 
> 	This is set in sparc/dev/zsvar.h ... and used in zs.c

The fixed `ring size' no longer exists. From the zs.c log:

  revision 1.32
  date: 1995/11/29 23:41:35;  author: pk;  state: Exp;  lines: +31 -15
  Extend the size of the "soft" FIFOs which reportedly reduces the number
  of FIFO overflows on high baud rates.
  However, doing so on all 4 ports would cost a whopping 64KB (at 4096 entries
  per FIFO) of kernel memory. So, the FIFOs are now allocated at attach time
  allowing the size for the keyboard and mouse ports to be reduced (to 128)
  which should be adequate for the 1200 baud they use.

-pk