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Altera_Forum
Honored Contributor
9 years agoFSM: a state gets latched
Hi, i am running a state machine. Simulation shows everything is OK. Real life implementation is showing otherwise. I keep track of the states using on board LEDS showing the current FSM st...
Altera_Forum
Honored Contributor
9 years ago --- Quote Start --- so as far as the FSM's concern, the trigger is synchronized. --- Quote End --- No, the positive transition of TRIG[0] is directly evaluated by the state machine logic without previous synchronization. trig_risedge_SI is generated in combinational logic. If the transition coincides with the active clock edge, delay skew can cause an inconsistent state variable result. --- Quote Start --- But maybe the synthesizer is changing my binary style i will try to look into that. --- Quote End --- It surely does, unless you specify an encoding by synthesis attributes. Review Quartus software manual about FSM coding styles. I can't say if the sketched problem is actually causing the observed FSM failure. But it surely can and is a "popular" fault when designing synchronous logic processing asynchronous input signals.