Waits

Two HDBs stall the flow: scWait waits for a condition, and syWait waits for a number of cycles. Both are single-statement blocks that hold the enclosing flow in place until their wait is satisfied.

#define scWait( cond) for(auto kathrynBlock = new FlowBlockCondWait(cond)  ; kathrynBlock->doPrePostFunction(); kathrynBlock->step()){};
#define syWait(cycle) for(auto kathrynBlock = new FlowBlockCycleWait(cycle); kathrynBlock->doPrePostFunction(); kathrynBlock->step()){};

scWait(cond) — wait for a condition

scWait(cond) elaborates to a Wait-Condition Node, which stalls execution until cond is satisfied. cond is any readable Kathryn signal or expression. From autoSim simAutoTest20, one par branch waits for a counter driven by the other branch:

seq {
    par{
        seq {
            scWait(a == 48);
            result = 1;
        }
        cwhile(a <= 50){
            a <<= a + 1;
        }
    }
}

The scWait(a == 48) holds its branch until the parallel loop has counted a up to 48; result = 1 then runs on the next cycle after the condition is met (the wait node is clocked — it releases the flow on the following clock edge, not in the same cycle the condition becomes true). This is the natural way to synchronize one flow against another’s progress.

syWait(N) — wait for a fixed cycle count

syWait(N) elaborates to a Wait-Cycle Node, which uses a counter and control logic to stall for a fixed number of cycles. The count may be a constant or a readable signal. From autoSim simAutoTest21, where the stall length comes from register a:

seq {
    a <<= 16;
    syWait(a);
    result = 1;
}

Here a <<= 16 runs, then syWait(a) stalls for the counted number of cycles before result = 1 fires.

flowchart TD
    ENTER["reach wait"] --> KIND{"which wait?"}
    KIND -->|"scWait(cond)"| WC["Wait-Condition Node"]
    KIND -->|"syWait(N)"| WY["Wait-Cycle Node<br/>(counter-based)"]
    WC --> C{"cond satisfied?"}
    C -->|no| WC
    C -->|"yes (next cycle)"| GO["continue flow"]
    WY --> D{"counter reached N?"}
    D -->|no| WY
    D -->|yes| GO

Choosing a wait

• Use scWait to synchronize against a data condition — another flow’s progress, an external ready signal, or any computed predicate.
• Use syWait for a deterministic delay of a known (or signal-driven) number of cycles, such as a bit period in a serial protocol.

Both waits nest inside any block; the simAutoTest71 UART loop in Loops uses syWait for its per-bit timing. For the underlying node mechanism see Nodes.