customasm is an assembler that allows you to provide your own custom instruction sets to assemble your source files! It can be useful, for example, if you're trying to test the bytecode of a new virtual machine, or if you're eager to write programs for that new microprocessor architecture you just implemented in an FPGA chip!

🖥️ Try it right now on your web browser!

🕹️ Check out an example project which targets the NES!

⌨️ Install the VSCode syntax highlight extension!

❤️ Support the author!

📚 Check out the wiki for a changelog, documentation, and a how-to-start guide!

💲 Check out the command-line help! (Better formatted on the command-line itself)

You can install directly from crates.io by running cargo install customasm. Then the customasm application should automatically become available in your command-line environment.

You can also download pre-built executables from the Releases section.

You can compile from source yourself by first cloning the repository and then simply running cargo build. There's also a battery of tests available at cargo test.

Given the following file:

#ruledef
{
    load r1, {value: i8} => 0x11 @ value
    load r2, {value: i8} => 0x12 @ value
    load r3, {value: i8} => 0x13 @ value
    add  r1, r2          => 0x21
    sub  r3, {value: i8} => 0x33 @ value
    jnz  {address: u16}  => 0x40 @ address
    ret                  => 0x50
}

multiply3x4:
    load r1, 0
    load r2, 3
    load r3, 4
    
    .loop:
        add r1, r2
        sub r3, 1
        jnz .loop
    
    ret

...the assembler will use the #ruledef directive to convert the instructions into binary code:

 outp | addr | data (base 16)

  0:0 |    0 |          ; multiply3x4:
  0:0 |    0 | 11 00    ; load r1, 0
  2:0 |    2 | 12 03    ; load r2, 3
  4:0 |    4 | 13 04    ; load r3, 4
  6:0 |    6 |          ; .loop:
  6:0 |    6 | 21       ; add r1, r2
  7:0 |    7 | 33 01    ; sub r3, 1
  9:0 |    9 | 40 00 06 ; jnz .loop
  c:0 |    c | 50       ; ret