🚀 go-pugleaf

In article <1ia62bINN37o@savoy.cc.williams.edu>, 93gke@williams.edu (oldwanda) writes:
|> I was wondering if anybody could help me with this. The docs for my
|> computer say that at 33Mhz I need 2 wait states. Any other speed works
|> at 0 wait states. Can someone explain this to me? I tried running at 0
|> and 1 wait states, but I had memory problems. This sucks! Would I
|> better off downgrading to 25Mhz??
|> 
Let me try with my limited hardware knowledge.

  With 33MHz, you are accessing the memory at (1/33E6)secs = 30.3 ns.
  That is too fast as most DRAMs can only provide access reliablity
  of 70/80ns (older DRAMs -> 100ns).

  Hence 2 wait states slows memory access to 90.9 ns which is ok for the
  70 and 80ns DRAMs.

  With 25MHz, it works out to 40ns and hence would need only 1 wait state.
  Not 0.

It is true that 25MHz machines access memory faster than 33MHz
machines (80 vs 90.9ns).  But then the uP also performs other
instructions as well.  My rough estimation would be about 30% on
memory fetches and 70% for other internal register manipulations. 
Which puts the 33MHz slightly ahead of the 25MHz.
 
Also I'm waiting for the day when they come out with 60ns DRAMs.  I can
then reduce my 33MHz to 1 wait state and see it fly :).

............................................................................
. Kyle Hor                    .    /       / _   .  Email  khor@bnr.ca     .
. Bell-Northern Research Ltd. .   /__\  / / /_\  .  Phone  (613) 763-2488  .
. Ottawa, Ontario, Canada     .  / \  \/ /  \__  .  ESN          393-2488  .
....................................__/.....................................
................  standard disclaimer, 2 cents opinion  ....................
.............  searching forever, for the perfect solution  ................