AR# 6286


Foundation 4.2i - If block statement structures use {,}s in ABEL state machine assignments, incorrect equations are produced


Keywords: XABEL, ABEL, .abl, state machine, goto, state equation, incorrect

Urgency: Standard

General Description:
When I use {,}s to enclose a state equation, the assignment is ignored.

For 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 the following equations:

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

instead of these expected equations:

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


According to ABEL syntax, the compiler is looking for a single state equation such as "State1" or "goto State1". Because the use of {,}s indicates the inclusion of multiple statements, they have no meaning in the ABEL syntax.

When {,}s are not used, the ABEL code will compile the correct equations. When {,}s are included, the condition attached to the statement is ignored.

If the state machine must transition to the next state with certain registers set, a "WITH" statement should be used.

(An enhancement request has been filed for the syntax checker so that an error or warning will be reported when {,}s are used in conjunction with state equations.)
AR# 6286
日期 08/12/2003
状态 Archive
Type 综合文章
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