BSV by Example - Computation Structures Group

ule r2;
let v1 = f1.first;
f1.deq;
$display (" v1 = %0h", v1);
f2.enq (v1+1);
endrule
rule r3;
let v2 = f2.first;
f2.deq;
$display (" v2 = %0h", v2);
f3.enq (v2+1);
endrule
rule r4;
let v3 = f3.first;
f3.deq;
$display (" v3 = %0h", v3);
f4.enq (v3+1);
endrule
The rules r2, r3, and r4 may or may not fire together. Each rule fires whenever its input FIFO
has data available (implicit condition of first and deq) and its output FIFO has space available
(implicit condition of enq).
The Action method send enqueues a value a into FIFO f1. This method is only enabled if f1 has
space available. Thus the implicit condition of f1.enq becomes the implicit condition of this send
method and becomes part of the enabling condition of the rule fill in the testbench, i.e., that rule
cannot fire unless the implicit conditions of f1.enq are met.
method Action send (int a);
f1.enq (a);
endmethod
The ActionValue method receive reads the first int element v4 of FIFO f4, dequeues FIFO f4 and
returns v4. This method is only enabled when f4 has data available (implicit condition of first
and deq). Thus the implicit conditions of f4.first and f4.deq become the implicit condition of
the receive method, which in turn becomes part of the enabling condition of rule drain in the
testbench. That is, the rule drain cannot fire until all these conditions are true.
method ActionValue#(int) receive ();
let v4 = f4.first;
$display (" v4 = %0h", v4);
f4.deq;
return v4;
endmethod
When executed, you can observe the pipeline behavior. However, the outputs from the $displays
in different rules that execute in the same cycle may be unpredictable.
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