AXI5-Stream EMA Filter

An AXI4/5-Stream exponential moving average (EMA) filter implemented in VHDL-2008.

How to use

Simply drop ema_filter.vhd into your project and instantiate the EMA filter component.

my_ema_filter: work.ema_filter
generic map (
    DATA_WIDTH => ...,  -- natural (default: 16).
    DATA_RADIX => ...,  -- natural (default: 0).
    ALPHA_WIDTH => ..., -- natural (default: `DATA_WIDTH`).
    ALPHA_RADIX => ...  -- natural (default: `DATA_RADIX`).
);
port (
    -- Interface global signals.
    aclk => ...,
    aresetn => ...,
    -- Input (AXI4/5-Stream).
    s_axis_e_tdata => ...,
    s_axis_e_tvalid => ...,
    -- Filtered output (AXI4/5-Stream).
    m_axis_u_tdata => ...,
    m_axis_u_tvalid => ...,
    -- EMA coefficient.
    alpha => ...
);

Documentation

Tip

This information can also be found in ema_filter.vhd.

An exponential moving average (EMA) filter.

An EMA filter produces an output, y, from an input x, using the equation:

y[t] = α*x[t] - (1 - α)*y[t-1]
     = y[t-1] + α*(x[t] - y[t-1])

where 0 ≤ α ≤ 1 is the smoothing factor. This implementation uses the second form of the equation above, which has one fewer multiplication.

The EMA filter clocks one data point in every 4 aclk cycles and clocks one out every 4 aclk cycles. If m_axis_y_tready is not asserted when the output is ready, that point is lost as no buffering is provided on the output.

Generics

• DATA_WIDTH: Width in bits of the input and output AXI4/5-Streams.
• DATA_RADIX: Radix position in bits of the fixed-point input and output AXI4/5-Streams.
• ALPHA_WIDTH: Width in bits of the input alpha coefficient.
• ALPHA_RADIX: Radix position in bits of the input alpha coefficient.

Ports

• aclk: Global AXI4/5-Stream clock.
• aresetn: Global active-low AXI4/5-Stream reset.
• s_axis_x_*: AXI4/5-Stream for the input signal as a signed fixed-point integer.
• m_axis_y_*: AXI4/5-Stream for the filtered output signal as a signed fixed-point integer.
• alpha: The smoothing factor, α, as a fixed-point integer.

Testing

The Makefile has the following recipes:

• make: Alias for make build.
• make build: Analyze and elaborate the source and test files.
• make test: Run the testbench.
• make wave: Display testbench waveforms.
• make clean: Remove all build artifacts.

Requirements

• GHDL is used for building and testing.
• GTKWave is used for viewing waveforms.

License

This project is distributed under the terms of the MIT License. The license text can be found in the LICENSE file of this repository.