JSON-for-VHDL by Paebbels

A JSON library implemented in VHDL


CLA assistant

JSON-for-VHDL is a library to parse and query JSON data structures in VHDL. The complete functionality is hosted in a single VHDL package, without special dependencies.

Table of Content:

  1. Overview
  2. JSON - JavaScript Object Notation
  3. Short Example
  4. Download

1 Overview

The JSON-for-VHDL library can be used to parse and query JSON data structures, which are read from disk. The data structure is read via VHDL file I/O functions and procedures and parsed into a internal compressed representation. While the parsing is done, a lightwight index is created to ease the navigation on the data structure.

Values can be selected by simple path expressions.

2 JSON - JavaScript Object Notation

JavaScript Object Notation (JSON) Data Interchange Format is specified in RFC 7159.

3 Short Example

Here is a short example *.json file, which describes two common FPGA boards.

{  "ML505": {
    "FPGA":        "XC5VLX50T-1FF1136",
    "Eth": [{
      "PHY-Int":   "GMII",
      "Device":    "MARVEL_88E1111",
      "Address":   "0x74"
  "KC705": {
    "FPGA":        "XC7K325T-2FFG900C",
    "Eth": [{
      "PHY-Int":   "GMII",
      "Device":    "MARVEL_88E1111",
      "Address":   "0x74"
    "IIC": [{
      "Type":      "Switch",
      "Adr":       "0x85",
      "Devices": [{
        "Name":    "Si570",
        "Address": "0x3A"

Reference the JSON package in VHDL:

use work.json.all;

Load a external *.json file, parse the data structure and select a value:

architecture rtl of Test is
  constant ConfigFile   : STRING    := "Boards.json";
  constant JSONContent	: T_JSON    := jsonLoad(ConfigFile);
  assert (JSONContent.Error(1) = C_JSON_NUL)
    report "Error: " & JSONContent.Error
    severity ERROR;
  assert FALSE
    report "Query='KC705/Eth/0/Address' Value='" & jsonGetString(JSONContent, "KC705/Eth/0/Address") & "'"
    severity NOTE;

  -- print the compressed file content
--  assert FALSE
--    report "JSON: " & JSONContent.Content severity NOTE;
end architecture;

4 Download

The library can be downloaded as a zip-file (latest 'master' branch) or cloned with git from GitHub. GitHub offers HTTPS and SSH as transfer protocols.

For SSH protocol use the URL ssh://git@github.com:Paebbels/JSON-for-VHDL.git or command line instruction:

cd <GitRoot>
git clone ssh://git@github.com:Paebbels/JSON-for-VHDL.git JSON

For HTTPS protocol use the URL https://github.com/Paebbels/JSON-for-VHDL.git or command line instruction:

cd <GitRoot>
git clone https://github.com/Paebbels/JSON-for-VHDL.git JSON

This is a local copy of the Apache License Version 2.0.
The original can be obtained here: http://www.apache.org/licenses/LICENSE-2.0

Apache License

Version 2.0, January 2004


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  • Registered on LibreCores 3 years ago
  • Project started 5 years ago
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