Transmit and Receive FIFO

This example shows how to generate HDL code from MATLAB® code modeling transfer data between transmit and receive FIFO.

Let us take a look at the MATLAB design for the transmit and receive FIFO and a testbench that exercises both designs.

design_core1 = 'mlhdlc_rx_fifo';
design_core2 = 'mlhdlc_tx_fifo';
testbench_name = 'mlhdlc_fifo_tb';

type('mlhdlc_rx_fifo');

function [dout, empty, byte_ready, full, bytes_available] = ...
    mlhdlc_rx_fifo(get_byte, store_byte, byte_in, reset_fifo, fifo_enable)
%

%   Copyright 2014-2015 The MathWorks, Inc.

%
%  First In First Out (FIFO) structure.
%  This FIFO stores integers.
%  The FIFO is actually a circular buffer.
%
persistent head tail fifo byte_out handshake

if (reset_fifo || isempty(head))
    head = 1;
    tail = 2;
    byte_out = 0;
    handshake = 0;
end

if isempty(fifo)
    fifo = zeros(1,1024);
end

full = 0;
empty = 0;
byte_ready = 0;

% Section for checking full and empty cases
if ((tail == 1 && head == 1024) || ((head + 1) == tail))
    empty = 1;
end
if ((head == 1 && tail == 1024) || ((tail + 1) == head))
    full = 1;
end

% handshaking logic
if get_byte == 0
    handshake = 0;
end
if handshake == 1
    byte_ready = 1;
end

if (fifo_enable == 1)
    %%%%%%%%%%%%%%get%%%%%%%%%%%%%%%%%%%%%
    if (get_byte && ~empty && handshake == 0 )
        head = head + 1;
        if head == 1025
            head = 1;
        end
        byte_out = fifo(head);
        byte_ready = 1;
        handshake = 1;
    end
    %%%%%%%%%%%%%put%%%%%%%%%%%%%%%%%%%%%
    if (store_byte && ~full)
        fifo(tail) = byte_in;
        tail = tail + 1;
        if tail == 1025
            tail = 1;
        end
    end
end

% Section for calculating num bytes in FIFO
if (head < tail)
    bytes_available = (tail - head) - 1;
else
    bytes_available = (1024 - head) + tail - 1;
end
    
dout = byte_out;
end

type('mlhdlc_tx_fifo');

function [dout, empty, byte_received, full, bytes_available, dbg_fifo_enable] = ...
    mlhdlc_tx_fifo(get_byte, store_byte, byte_in, reset_fifo, fifo_enable)
%

%   Copyright 2014-2015 The MathWorks, Inc.

%
%  First In First Out (FIFO) structure.
%  This FIFO stores integers.
%  The FIFO is actually a circular buffer.
%
persistent head tail fifo byte_out handshake

if (reset_fifo || isempty(head))
    head = 1;
    tail = 2;
    byte_out = 0;
    handshake = 0;
end

if isempty(fifo)
    fifo = zeros(1,1024);
end

full = 0;
empty = 0;
byte_received = 0;

% Section for checking full and empty cases
if ((tail == 1 && head == 1024) || ((head + 1) == tail))
    empty = 1;
end
if ((head == 1 && tail == 1024) || ((tail + 1) == head))
    full = 1;
end

% handshaking logic
if store_byte == 0
    handshake = 0;
end
if handshake == 1
    byte_received = 1;
end

if (fifo_enable == 1)
    %%%%%%%%%%%%%%get%%%%%%%%%%%%%%%%%%%%%
    if (get_byte && ~empty)
        head = head + 1;
        if head == 1025
            head = 1;
        end
        byte_out = fifo(head);
    end
    %%%%%%%%%%%%%put%%%%%%%%%%%%%%%%%%%%%
    if (store_byte && ~full && handshake == 0)
        fifo(tail) = byte_in;
        tail = tail + 1;
        if tail == 1025
            tail = 1;
        end
        byte_received = 1;
        handshake = 1;
    end
end

% Section for calculating num bytes in FIFO
if (head < tail)
    bytes_available = (tail - head) - 1;
else
    bytes_available = (1024 - head) + tail - 1;
end

dout = byte_out;
dbg_fifo_enable = fifo_enable;
end

type('mlhdlc_fifo_tb');

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% simulation parameters
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% data payload creation

%   Copyright 2014-2015 The MathWorks, Inc.

messageASCII = 'Hello World!';
message = double(unicode2native(messageASCII));
msgLength = length(message);
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% TX_FIFO core
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
numBytesToFifo = 1;
tx_get_byte = 0;
tx_full = 0;
tx_byte_received = 0;
i1 = 1;

while (numBytesToFifo <= msgLength && ~tx_full)
    % first thing the processor does is clear the internal tx fifo
    if i1 == 1
        tx_reset_fifo = 1;
        mlhdlc_tx_fifo(0, 0, 0, tx_reset_fifo, 1);
    else
        tx_reset_fifo = 0;
    end
    if (i1 > 1)
        tx_data_in = message(numBytesToFifo);
        numBytesToFifo = numBytesToFifo + 1;
        tx_store_byte = 1;
        while (tx_byte_received == 0)
            [tx_data_out, tx_empty, tx_byte_received, tx_full, tx_bytes_available] = ...
                mlhdlc_tx_fifo(tx_get_byte, tx_store_byte, tx_data_in, tx_reset_fifo, 1);
        end
        tx_store_byte = 0;
        while (tx_byte_received == 1)
            [tx_data_out, tx_empty, tx_byte_received, tx_full, tx_bytes_available] = ...
                mlhdlc_tx_fifo(tx_get_byte, tx_store_byte, tx_data_in, tx_reset_fifo, 1);
        end
    end
    i1 = i1 + 1;
end
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% Transfer Bytes from TX FIFO to RX FIFO
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
i1 = 1;

tx_get_byte = 0;
tx_store_byte = 0;
tx_data_in = 0;
tx_reset_fifo = 0;

rx_get_byte = 0;
rx_data_in = 0;
rx_reset_fifo = 0;

while (tx_bytes_available > 0)
        if i1 == 1
            rx_reset_fifo = 1;
            mlhdlc_rx_fifo(0, 0, 0, rx_reset_fifo, 1);
        else
            rx_reset_fifo = 0;
        end
        if (i1 > 1)
            tx_get_byte = 1;
            rx_store_byte = 1;
            [tx_data_out, tx_empty, tx_byte_received, tx_full, tx_bytes_available] = ...
                mlhdlc_tx_fifo(tx_get_byte, tx_store_byte, tx_data_in, tx_reset_fifo, 1);
            
            rx_data_in = tx_data_out;
            
            [rx_data_out, rx_empty, rx_byte_ready, rx_full, rx_bytes_available] = ...
                mlhdlc_rx_fifo(rx_get_byte, rx_store_byte, rx_data_in, rx_reset_fifo, 1);
        end
        i1 = i1 + 1;
end
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% RX_FIFO core
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
numBytesFromFifo = 1;
rx_store_byte = 0;
rx_byte_recieved = 0;
i1 = 1;
msgBytes = zeros(1,msgLength);

while (~rx_empty)
    % first thing the processor does is clear the internal rx fifo
    if (i1 > 1)
        rx_get_byte = 1;
        while (rx_byte_ready == 0)
            [rx_data_out, rx_empty, rx_byte_ready, rx_full, rx_bytes_available] = ...
                mlhdlc_rx_fifo(rx_get_byte, rx_store_byte, rx_data_in, rx_reset_fifo, 1);
        end
        msgBytes(i1-1) = rx_data_out;
        rx_get_byte = 0;
        while (rx_byte_ready == 1)
            [rx_data_out, rx_empty, rx_byte_ready, rx_full, rx_bytes_available] = ...
                mlhdlc_rx_fifo(rx_get_byte, rx_store_byte, rx_data_in, rx_reset_fifo, 1);
        end
    end
    i1 = i1 + 1;
end
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

numRecBytes = numBytesFromFifo;
if sum(msgBytes-message) == 0
    disp('Received message correctly');
else
    disp('Received message incorrectly');
end    
native2unicode(msgBytes)

Create a New Folder and Copy Relevant Files

Execute the following lines of code to copy the necessary example files into a temporary folder.

mlhdlc_demo_dir = fullfile(matlabroot, 'toolbox', 'hdlcoder', 'hdlcoderdemos', 'matlabhdlcoderdemos');
mlhdlc_temp_dir = [tempdir 'mlhdlc_fifo'];

% Create a temporary folder and copy the MATLAB files.
cd(tempdir);
[~, ~, ~] = rmdir(mlhdlc_temp_dir, 's');
mkdir(mlhdlc_temp_dir);
cd(mlhdlc_temp_dir);

copyfile(fullfile(mlhdlc_demo_dir, 'mlhdlc_fifo_tb.m*'), mlhdlc_temp_dir);
copyfile(fullfile(mlhdlc_demo_dir, 'mlhdlc_rx_fifo.m*'), mlhdlc_temp_dir);
copyfile(fullfile(mlhdlc_demo_dir, 'mlhdlc_tx_fifo.m*'), mlhdlc_temp_dir);

% Additional test files
copyfile(fullfile(mlhdlc_demo_dir, 'mlhdlc_rx_fifo_tb.m*'), mlhdlc_temp_dir);
copyfile(fullfile(mlhdlc_demo_dir, 'mlhdlc_tx_fifo_tb.m*'), mlhdlc_temp_dir);

Simulate the Design

It is always a good practice to simulate the design with the testbench prior to code generation to make sure there are no runtime errors.

mlhdlc_fifo_tb

Received message correctly

ans =

    'Hello World!'

Create a New HDL Coder™ Project

coder -hdlcoder -new mlhdlc_fifo

Next, add the file 'mlhdlc_fifo.m' to the project as the MATLAB Function and 'mlhdlc_fifo_tb.m' as the MATLAB Test Bench.

Refer to Getting Started with MATLAB to HDL Workflow for a more complete tutorial on creating and populating MATLAB HDL Coder projects.

Run Fixed-Point Conversion and HDL Code Generation

Launch the Workflow Advisor from the Build tab and right click on the 'Code Generation' step and choose the option 'Run to selected task' to run all the steps from the beginning through the HDL code generation.

Examine the generated HDL code by clicking on the hyperlinks in the Code Generation Log window.

Clean up the Generated Files

You can run the following commands to clean up the temporary project folder.

mlhdlc_demo_dir = fullfile(matlabroot, 'toolbox', 'hdlcoder', 'hdlcoderdemos', 'matlabhdlcoderdemos');
mlhdlc_temp_dir = [tempdir 'mlhdlc_fifo'];
clear mex;
cd (mlhdlc_demo_dir);
rmdir(mlhdlc_temp_dir, 's');

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