Json in VHDL

VHDL offers support for JSON-like data structures through custom types and functions. While VHDL doesn’t have built-in JSON support, we can simulate JSON-like functionality using records and arrays.

library IEEE;
use IEEE.std_logic_1164.all;
use IEEE.numeric_std.all;

entity json_example is
end entity;

architecture behavior of json_example is
    -- Define custom types to simulate JSON-like structures
    type string_array is array (natural range <>) of string(1 to 20);
    
    type response1 is record
        Page   : integer;
        Fruits : string_array(1 to 3);
    end record;
    
    type response2 is record
        page   : integer;
        fruits : string_array(1 to 3);
    end record;
    
    -- Function to simulate JSON encoding
    function encode_response1(resp : response1) return string is
    begin
        return "{""Page"":" & integer'image(resp.Page) & 
               ",""Fruits"":[""" & resp.Fruits(1) & """,""" & 
               resp.Fruits(2) & """,""" & resp.Fruits(3) & """]}";
    end function;
    
    -- Function to simulate JSON decoding
    procedure decode_response2(json_str : in string; resp : out response2) is
    begin
        -- This is a simplified decoding, assuming a fixed format
        resp.page := to_integer(unsigned(json_str(8 to 8)));
        resp.fruits(1) := json_str(21 to 25);
        resp.fruits(2) := json_str(28 to 32);
        resp.fruits(3) := json_str(35 to 38);
    end procedure;

begin
    process
        variable res1 : response1;
        variable res2 : response2;
        variable json_str : string(1 to 100);
    begin
        -- Simulating JSON encoding
        res1.Page := 1;
        res1.Fruits(1) := "apple               ";
        res1.Fruits(2) := "peach               ";
        res1.Fruits(3) := "pear                ";
        
        json_str := encode_response1(res1);
        report "Encoded JSON: " & json_str;
        
        -- Simulating JSON decoding
        json_str := "{""page"":1,""fruits"":[""apple"",""peach"",""pear""]}";
        decode_response2(json_str, res2);
        
        report "Decoded page: " & integer'image(res2.page);
        report "Decoded fruit 1: " & res2.fruits(1);
        report "Decoded fruit 2: " & res2.fruits(2);
        report "Decoded fruit 3: " & res2.fruits(3);
        
        wait;
    end process;
end architecture;

In this VHDL example, we’ve created custom types and functions to simulate JSON-like behavior:

We define custom types string_array, response1, and response2 to represent JSON-like structures.
The encode_response1 function simulates JSON encoding by creating a JSON-like string from a response1 record.
The decode_response2 procedure simulates JSON decoding by parsing a JSON-like string into a response2 record.
In the main process, we demonstrate both encoding and decoding:
- We create a response1 variable, populate it with data, and then encode it to a JSON-like string.
- We then simulate decoding a JSON-like string into a response2 variable.

This example shows how to work with JSON-like data structures in VHDL, even though VHDL doesn’t have native JSON support. In practice, more robust parsing and encoding would be needed for real-world applications.

To run this VHDL code, you would typically use a VHDL simulator such as ModelSim or GHDL. The simulation would show the report messages with the encoded and decoded data.

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