HDL Compiler

Compiler for a self-invented hardware description language
README from GitLab:


Compiler for a self-invented hardware description language.

The front end uses a hand-written recursive descent parser (LL(1)) to parse the source language, does semantic analysis and emits intermediate code. This intermediate code is then linked and can be translated to different target formats.

Compiler usage

The compiler consists of a single executable, hdlc. It handles parsing, intermediate code generation, linking and target code generation.

  hdlc [option]... <file>...

  -x <type>     Treat subsequent input files as having type <type>.
                Available types are: 'auto' (default), 'hdl', 'intermediate'
                If 'auto' is specified, the type is guessed based on the file extension.
  -d            Treat all input files as intermediate code and dump them.
  -c            Compile each input file separately to intermediate code.
  -l            Compile the input files to intermediate code and link them, but don't run the backend.
  -b <backend>  Use a specific backend.
                Available backends are: 'LogicSimulator' (default), 'csim'
  -o <file>     Write output to <file>.
  -B <arg>      Pass argument <arg> to the backend.
  -v[level]     Print more log messages.
  -V, --version Display version information and exit.
  -h, --help    Display this help and exit.

Each input file is first compiled to intermediate code internally. Source files will be parsed, analyzed and compiled to intermediate code. Intermediate code files will just be read into memory. If the -c flag was passed, the compilation process ends here and the intermediate code files are written to disk.

All the intermediate code files will then be linked together to a single file. If the -l flag was passed, this file will be written to disk and no further processing will be done.

Then, the backend specified with the -b flag (LogicSimulator by default) is invoked, which compiles the single intermediate file to the target format.

The complete compilation process looks like this:

 +-------------+    /-----------\    +-------------------+
 | source file | -> | front end | -> | intermediate code | -+
 +-------------+    \-----------/    +-------------------+  |   /--------\    +-------------------+    /----------\    +-------------+
                                                            +-> | linker | -> | intermediate code | -> | back end | -> | target file |
                                     +-------------------+  |   \--------/    +-------------------+    \----------/    +-------------+
                                     | intermediate code | -+
                                     +-------------------+  |



The compiler supports different compilation backends:


This backend generates circuits for https://github.com/LogicSimulator, my editor and simulator for digital circuits.

It produces a .json file, which can be loaded in the simulator by pressing the folder icon in the top left corner.

The leftmost vertical signals are the inputs followed by the outputs of the circuit. For example, if a circuit is generated from the following description:

block main {
    in a;
    in[2] b;
    out q;
    out[2] r;

    q = a;
    r = b;

it will have 3 input signals and 3 output signals. The leftmost signal corresponds to input a. The next two signals correspond to input b with the least-significant bit first. The fourth signal from the left is output q, followed by two signals for output r.

The backend generates toggle buttons and LEDs for the inputs/outputs of the main block. You can pass it the flag --no-io-components (e.g. hdlc -B --no-io-components circuit.hdl) if you don't want that.

Invocation examples

Compile a single source file, a.hdl, to a LogicSimulator circuit, circuit.json:

hdlc a.hdl

Compile two source files, a.hdl and b.hdl, to a LogicSimulator circuit, a_and_b.json:

hdlc a.hdl b.hdl -o a_and_b.json

Compile two source files, a.hdl and b.hdl, to separate intermediate code files, a.hdli and b.hdli:

hdlc -c a.hdl b.hdl

Link two intermediate code files, a.hdli and b.hdli, and write the resulting intermediate code file to a_and_b.hdli:

hdlc -l a.hdl b.hdl -o a_and_b.hdli

Compile one intermediate code file, a_and_b.hdli, to a LogicSimulator circuit, a_and_b.json:

hdlc a_and_b.hdli -o a_and_b.json

The language

The hardware description languages syntax is inspired by C. Blocks are surrounded by braces, statements are terminated with semicolons.

A circuit is composed of named "blocks". A single .hdl file can contain multiple block definitions. Each block has inputs and outputs, which have names and can be of any width (other than zero, obviously). It can also make use of other blocks, which enables a very modular structure. The inputs, outputs and used blocks have to be declared at the start of a block:

block some_block {
    in a, b;
    in[25] wide_input, anotherWideInput;
    out[2] Q, output2;
    block some_other_block b1, b2;

Each circuit has to have exactly one block named "main".

Following the declarations, the behaviour of the block is specified. You can write simple assignment statements, with an output on the left and an expression on the right. Available operators are the binary operators & (AND), | (OR) and ^ (XOR) and the unary operator ~ (NOT). If the operands are multiple bits wide, the operators apply to each bit individually. Sub-expressions can be parenthesized. Operands can either be number literals or identifiers. You can extract a single or multiple bits from a signal with "array accesses". Use id[index] to access a single bit and id[index:index] to access a range of bits (the left index must be the higher one). To access inputs and outputs of a sub-block, use the name of the block followed by a dot and the input/output name: block_name.input_or_output_name.

As a complete example take this 4-bit adder, which combines four single-bit adders:

block adder {
    in a, b, c_in;
    out s, c_out;

    s = a ^ b ^ c_in;
    c_out = a & b | c_in & (a ^ b);

block main {
    in[4] a, b;
    in c_in;
    out[4] s;
    out c_out;
    block adder adder0, adder1, adder2, adder3;

    adder0.a = a[0];
    adder0.b = b[0];
    adder0.c_in = c_in;
    s[0] = adder0.s;

    adder1.a = a[1];
    adder1.b = b[1];
    adder1.c_in = adder0.c_out;
    s[1] = adder1.s;

    adder2.a = a[2];
    adder2.b = b[2];
    adder2.c_in = adder1.c_out;
    s[2] = adder2.s;

    adder3.a = a[3];
    adder3.b = b[3];
    adder3.c_in = adder2.c_out;
    s[3] = adder3.s;

    c_out = adder3.c_out;


The project uses the CMake build system. You need CMake itself and a C compiler (e.g. Clang or GCC).

It can be built like the following:

mkdir build && cd build
cmake -DCMAKE_BUILD_TYPE=Release ..

The executable is then located at build/bin/hdlc.