AXI5-Stream PID Controller

An AXI4/5-Stream PID controller implemented in VHDL-2008.

How to use

Simply drop pid_controller.vhd into your project and instantiate the PID controller component.

my_pid_controller: entity work.pid_controller
generic map (
    DATA_WIDTH => ...,      -- natural (default: 16).
    DATA_RADIX => ...,      -- natural (default: 0).
    K_WIDTH => ...,         -- natural (default: `DATA_WIDTH`).
    K_RADIX => ...,         -- natural (default: `DATA_RADIX`).
    INTEGRATOR_WIDTH => ... -- natural: (default `DATA_WIDTH`).
)
port map (
    -- Interface global signals.
    aclk => ...,
    aresetn => ...,
    -- Error signal input (AXI4/5-Stream).
    s_axis_e_tdata => ...,
    s_axis_e_tvalid => ...,
    -- Control variable output (AXI4/5-Stream).
    m_axis_u_tdata => ...,
    m_axis_u_tvalid => ...,
    -- PID coefficients.
    kp => ...,
    ki => ...,
    kd => ...
);

Documentation

Tip

This information can also be found in pid_controller.vhd.

This controller implements the following system, where e(t) is the input error signal and u(t) is the computed control variable that feeds back to the system. The PID coefficients kp, ki, and kd define the loop.

        +---> kp * e(t) --------+
        |                       |
e(t) ---+---> ki * ∫e(t) dt --> Σ ---> u(t)
        |                       |
        +---> kd * e(t)/dt -----+

The PID controller is used in the following way, where r(t) is the setpoint and y(t) is the process variable. The error signal fed to the PID controller is generally computed in the same way from the setpoint and process variable (often as the difference).

            e(t)                u(t)
s(t) ---> Σ ---> PID Controller ---> Process --+-> y(t)
          |                                    |
          +------------------------------------+

The PID controller accepts e(t) rather than s(t), so it is possible to generate error signals using more sophisticated approaches.

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.
• K_WIDTH: Width in bits of the input kp, ki, and kd coefficients.
• K_RADIX: Radix position in bits of the input kp, ki, and kd coefficients.
• INTEGRATOR_WIDTH: Width in bits of the internal integrator. Can be used to set the integrator width larger than DATA_WIDTH to prevent early saturation of the integrator.

Ports

• aclk: Global AXI4/5-Stream clock.
• aresetn: Global active-low AXI4/5-Stream reset.
• s_axis_e_*: AXI4/5-Stream for the error signal input as a signed fixed-point integer.
• m_axis_u_*: AXI4/5-Stream for the control variable output as a signed fixed-point integer.
• kp: Proportional coefficient as a signed fixed-point integer.
• ki: Integral coefficient as a signed fixed-point integer.
• kd: Derivative coefficient as a signed 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.