Registers

A register provides the means to maintain persistent state.

Register Creation

A register can be defined inside a process.

reg-creation ::= reg $identifier : $data-type-expression [$param-vals] ;

The statement reg r : dtype; defines a new register with identifier r and data type dtype.

Register Read

A register can be read using the * operator.

reg-read-expression ::= *$identifier

The expression *r evaluates immediately to the current value of the register r. The value remains available until the next write to r.

Upon reset, the initial value of a register is all zeros.

Register Write

A register can be written using the set expression.

set-expression ::= set $lval := $expression
lval ::= $identifier | $lval.$identifier | $lval [ $expression ] | $lval [ $expression+:{$digit}+ ]

The set expression evaluates to () delayed by one cycle. All expressions involved must have been evaluated and must have valid results. The new value of the register becomes visible in the next cycle.

For example, set r := e writes the evaluated result of e to the register r after one cycle.