Xilinx Answer #6286 : F1.5iS2: Using block statement structures using {,}s in Abel state machine assignments may cause incorrect equations

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F1.5iS2: Using block statement structures using {,}s in Abel state machine assignments may cause incorrect equations

Record #6286
Product Family: Software

Product Line: Data I/O

Product Part: xabel

Problem Title:

F1.5iS2: Using block statement structures using {,}s in Abel state machine assignments may cause incorrect equations

Problem Description:
Urgency: Standard

General Description: Using {,}s to enclose a state equation will
cause the assignement to be ignored.

Example:

state_diagram Sreg
       async_reset InitState : CLR;

       state InitState: if !(A # B) then InitState;
                 else if (A) then {goto State1;}
                 else {goto State2;}
      state State1: goto InitState;
      state State2: goto InitState;

"The simple state machine coded above will produce equations:

" State1.D = (InitState.Q); " State2.D = (InitState.Q);

"Instead of the expected equations:

" State1.D = (InitState.Q & A); " State2.D = (InitState.Q & !A & B);

Solution 1:

According to ABEL syntax, the compiler is looking for a single state equation
suchas 'State1' or 'goto State1' therefore the use of {,}s, which indicates the inclusion of multiple statements, is of no meaning.

Without the {,}s the abel code is compiled to the correct equations.
When the {,}s are included, the condition attached to the statement is ignored.

If the state machine needs to transition to the next state with ceritain registers set then a 'WITH' statement should be used.

An enhancement request has been filed for the syntax checker to produce an
error or warning when {,}s in conjunction with state equations.

End of Record #6286 - Last Modified: 04/26/99 08:49

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