Memory-backed streaming component

Consider a component with a packet stream, an Avalon-MM control port, external memory masters, two clock domains and an interrupt. Several coefficient arrays live in external memory; scalar coefficients and mode selection live in registers. One command can also update a coefficient array from captured frames.

The case study focuses on keeping all observable state coherent.

Separate four kinds of state

Treat these state groups explicitly:

1. register state owned by the behavior model;
2. coefficient arrays stored in the memory model;
3. transient command state and completion events;
4. protocol context such as the active control geometry.

Reset may affect these groups differently. For example, registers and pending commands can reset while external memory contents survive. on_reset() must follow the RTL contract rather than clearing every Python object indiscriminately.

Keep memory and prediction coherent

Use one helper whenever a test installs a coefficient array:

def set_coefficient(self, address, values):
    self.memory.write(address, values.tobytes())
    self.behavior_model.set_coefficient(address, values)

Updating only memory or only the behavior model creates a false comparison. Runtime address changes should select the same array in both the DUT-visible memory map and the prediction state.

Model commands in phases

A long-running update command often has three distinct model operations:

• predict the result without changing state;
• compare memory, status and interrupt outputs from the DUT;
• commit the checked result as the next active coefficient state.

Keeping prediction and commit separate prevents the model from moving ahead of an operation that has not completed.

Useful scenarios

• stream passthrough and active modes;
• each coefficient group independently and in combination;
• default and runtime memory addresses;
• command completion, status and interrupt acknowledgement;
• randomized memory latency and stream backpressure;
• unsupported frame geometry followed by a valid frame;
• reset during an in-flight stream packet;
• reset-state versus retained-memory behavior.