Blocking Reads and Writes - 2021.1 English

Vitis High-Level Synthesis User Guide (UG1399)

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2021.1 English

The basic accesses to an hls::stream<> object are blocking reads and writes. These are accomplished using class methods. These methods stall (block) execution if a read is attempted on an empty stream FIFO, a write is attempted to a full stream FIFO, or until a full handshake is accomplished for a stream mapped to an ap_hs interface protocol.

A stall can be observed in C/RTL co-simulation as the continued execution of the simulator without any progress in the transactions. The following shows a classic example of a stall situation, where the RTL simulation time keeps increasing, but there is no progress in the inter or intra transactions:

// RTL Simulation : "Inter-Transaction Progress" ["Intra-Transaction Progress"] @ 
"Simulation Time"
// RTL Simulation : 0 / 1 [0.00%] @ "110000"
// RTL Simulation : 0 / 1 [0.00%] @ "202000"
// RTL Simulation : 0 / 1 [0.00%] @ "404000"