Wait States


The GG2 Bus+ board includes support for PC bus wait states.  These occur 
when a plug-in card is too slow for the host computer, and issues a signal
for the host to "wait" a certain number of clock cycles in order to keep up.
Unfortunately, the PC bus method of asking for wait states is different from
that on the Amiga Zorro II bus.  The GG2 Bus+ board must therefore provide 
translation between the two systems.

Because the PC bus cycle is normally much longer than a Zorro II bus cycle,
providing this wait state translation requires "stretching" the Amiga bus 
cycle a small amount (one Amiga bus cycle, or 140 ns) with 
each access of the GG2 Bus+ board, in effect generating one Amiga wait state 
regardless of whether the PC card requests any or not.  A wait state request
from a PC plug-in board will then elongate the GG2 Bus+ bus cycle further as
required.

If you do not have any PC cards in your system that use wait states and your 
PC cards are fast, you may be able to have all your bus accesses done with 
"zero wait states" on the Amiga side.  In this mode, there is no "stretching"
of the Amiga bus cycle to accommodate PC bus wait states, and any PC card wait
state requests will be ignored.  To turn on or off wait state support, you 
must do a read or write access to Register 3 (see Appendix B).  Successive 
accesses to Register 3 will toggle wait state support on or off.  You can 
check whether wait states are enabled by checking bit 1 of Register 1.  A zero
value for this bit means wait states are disabled, a one means they are 
enabled.  The program  SwitchControl  included in the software package allows
you to easily enable or disable wait states.  Once wait states are enabled,
every bus access to the GG2 Bus+ card is slightly elongated, and any PC card
wait state requests will be accepted and translated to Amiga Zorro II wait
states.

The jumper on the GG2 Bus+ board labeled "Wait State Default" (on the end 
of the board nearest the back of your machine) controls the mode that the 
board defaults to with any system reset.  Usually, this jumper should remain 
set to "on" to always enable wait states.  Consult the "Installation" section
of this manual to see if you can change this jumper on your machine.  If your 
machine can handle zero wait state operation, you will have to check if your 
PC card is fast enough by experimenting a bit. 

Try using the  SwitchControl  program to turn off wait states and see 
if you can run your card without errors.  If you experience no problems, you 
might consider changing the "Wait State Default" jumper to the "off" setting.