Parameterizable Accumulator - 2022.1 English

Vitis Model Composer User Guide (UG1483)

Document ID
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2022.1 English

This example shows how to use the MCode block to build an accumulator using persistent state variables and parameters to provide implementation flexibility. The following M-code, which defines function xl_accum is contained in file xl_accum.m:

function q = xl_accum(b, rst, load, en, nbits, ov, op, feed_back_down_scale)
% q = xl_accum(b, rst, nbits, ov, op, feed_back_down_scale) is
% equivalent to our Accumulator block.
  binpt = xl_binpt(b);
  init = 0;
  precision = {xlSigned, nbits, binpt, xlTruncate, ov};
  persistent s, s = xl_state(init, precision);
  q = s;
  if rst
    if load
      % reset from the input port
      s = b;
      % reset from zero
      s = init;
    if ~en
      % if enabled, update the state
      if op==0
        s = s/feed_back_down_scale + b;
        s = s/feed_back_down_scale - b;

The following diagram shows a Subsystem containing the accumulator MCode block using M-function xl_accum. The MCode block is labeled MCode Accumulator. The Subsystem also contains the Xilinx Accumulator block, labeled Accumulator, for comparison purposes. The MCode block provides the same functionality as the Xilinx Accumulator block; however, its mask interface differs in that parameters of the MCode block are specified with a cell array in the Function Parameter Bindings parameter.

Figure 1. MCode Accumulator

Optional inputs rst and load of block Accum_MCode1 are disabled in the cell array of the Function Parameter Bindings parameter. The block mask for block MCode Accumulator is shown below:

Figure 2. Mask for MCode Accumulator

The example contains two additional accumulator Subsystems with MCode blocks using the same M-function, but different parameter settings to accomplish different accumulator implementations.