Avalon Verification IP Suite: User Guide

ID 683439
Date 2/17/2022
Public
Document Table of Contents

18.2.4. Observing the Results

You can view the simulation results in the following two ways:
  • In the ModelSim transcript console
  • In the waveforms window

The transcript ModelSim transcript provides the following information:

  • When the Avalon-ST source BFM drives a transaction, it also prints the transaction to the ModelSim transcript window.
  • The Avalon-ST Sink BFM also prints the transactions it receives on the transcript window.
  • The Avalon-ST Sink BFM compares the transaction it receives with the one sent by the Avalon-ST Source BFM. The results of the comparison are printed on the transcript window.
  • The idles values for the source and sink are different:
    • The Avalon-ST Source BFM sets the number of idle cycles to zero using the set_transaction_idles function.
    • The Avalon-ST Sink BFM waits for three cycles before receiving the first transaction. The three-cycle delay is necessary for the transaction to propagate from the input to the output of the sink FIFO buffer.
    • The difference in values for the idle field is not an error. The Avalon-ST interface protocol allows source and sink components to have different latencies.

The following example shows the ModelSim transcript for the source response latency. This latency is the number of clock cycles the Avalon-ST Single-Clock FIFO buffer takes when the Avalon-ST Single-Clock FIFO buffer backpressures the Avalon-ST Source BFM. The third response shows a non-zero response latency. During the third transaction, the Avalon-ST Single-Clock FIFO buffer is full. It is not able to receive the transaction. As a result, the Avalon-ST Single-Clock FIFO buffer backpressures the Avalon-ST Source BFM.

# 1030000:INFO:top.pgm.test_threads.source_response_thread: Source response latency 0 
# 1050000:INFO:top.pgm.test_threads.source_response_thread: Source response latency 0 
# 1090000:INFO:top.pgm.test_threads.source_response_thread: Source response latency 1 
# 1110000:INFO:top.pgm.test_threads.source_response_thread: Source response latency 0
Figure 27. Timing from ModelSim SimulationThis figure shows the simulation timing from the ModelSim wave window.

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