When can I use AFTER Xns; or FOR Xns; ????

[buckeyes1997]

I have tried using these in QUARTUSII inside a process that has a
sensativity list and it errors during compiling. I have also tried it
in a process with no sensativity list (using wait until) and it still
gives an error saying that must use wait until rather than wait for
Xns.

inside a process i want to pause it for a small amount of time before
going on and cant seem to make the built in WAIT statements do it. Any
thoughts??

THANKS
matt

 

[Mike Treseler]

buckeyes1997 wrote:

I have tried using these in QUARTUSII inside a process that has a
sensativity list and it errors during compiling. I have also tried it
in a process with no sensativity list (using wait until) and it still
gives an error saying that must use wait until rather than wait for
Xns.

Synthesize an example first.

inside a process i want to pause it for a small amount of time before
going on and cant seem to make the built in WAIT statements do it. Any
thoughts??

Modelsim will wait, but synthesis doesn't know how.
Describe a counter or shift register in your design.

-- Mike Treseler

 

[Niv]

Think hardware! How can a piece of hardware wait for "n" nanoseconds?
This will not synthesise.

However, WAIT UNTIL will wait for an event on a signal, so is quite
legal to synthesise.
As Mike says, try a counter, shift reg or something to wait for a fixed
number of clock cycles or whatever.