Bus ResolutionSmoke Generator

• VHDL does not allow multiple concurrent signal assignments to the same signal

  • Multiple sequential signal assignments are allowed

LIBRARY attlib; USE attlib.att_mvl.ALL;

-- this code will generate an error

ENTITY bus IS

PORT (a, b, c : IN MVL; z : OUT MVL);

END bus;

ARCHITECTURE smoke_generator OF bus IS

SIGNAL circuit_node : MVL;

BEGIN

circuit_node <= a;

circuit_node <= b;

circuit_node <= c;

z <= circuit_node;

END smoke_generator;

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Each concurrent signal assignment statement or process has a driver for any signal being assigned. Special care must be used when multiple concurrent signal assignment statements and/or processes drives the same signal.

Note that multiple signal assignment statements within the same process (i.e. sequential signal assignment statements) are allowed because they are executed sequentially and all use the one signal driver of their process.