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Activation Module

Description

The Activation Module (hs_npu_activation) processes data by applying an activation function (currently ReLU) and performs quantization through a configurable right shift operation. This module allows for flexible activation functions, with ReLU being implemented as a basic function. Quantization is achieved by truncating the shifted output data to the desired width, specified by the OUTPUT_WIDTH parameter.

Note

Future support for additional activation functions can be easily integrated using look-up tables, which allow efficient management and implementation of multiple activation methods.

I/O Table

Input Table

Input Name Direction Type Description
input_data Input logic[DATA_WIDTH-1:0] Data to be processed by the activation function.
valid_i Input logic Signal indicating the input data is valid.
relu_en Input logic Enable signal for applying ReLU activation; if low, data passes unmodified.
shift_amount Input logic[DATA_WIDTH-1:0] Shift value to control the level of quantization in the output.

Output Table

Output Name Direction Type Description
result Output logic[OUTPUT_WIDTH-1:0] Quantized output after activation and shift, truncated to OUTPUT_WIDTH bits.
valid_o Output logic Valid signal indicating the output is ready.

Module Behavior and Data Flow

  1. ReLU Activation: When relu_en is high, the ReLU function is applied to input_data. The module outputs the maximum of input_data and 0, effectively setting negative values to zero. If relu_en is low, the module bypasses ReLU and passes input_data directly to the next step.

  2. Quantization via Right Shift: The processed data then undergoes an arithmetic right shift by the value specified in shift_amount. This step performs quantization, reducing the precision of the data to fit within OUTPUT_WIDTH bits.

  3. Truncation to Output Width: After shifting, the result is truncated to OUTPUT_WIDTH bits, producing the quantized output in result. The valid_o signal indicates that the result is ready.

Example: ReLU and Shift Logic

If valid_i is asserted:

  • When relu_en is high:

    • relu_result = max(input_data, 0)

  • If relu_en is low:

    • relu_result = input_data

  • Shift: The relu_result is then right-shifted by shift_amount.

  • Output: The shifted data is truncated to OUTPUT_WIDTH bits and assigned to result, with valid_o set high.

Diagram

The diagram is trivial.

File Name Type
hs_npu_activation Top Module