This (originally) was a fun little project I did in 2 weeks on vacation out of boredom, however it has now been expanded with many more hours invested into it. The JoltCore 16 (JC16v2) is an evolution of my original 8-bit CPU + it's 16-bit, now, has 8 general purpose registers, several I/O ports, up to 128 KiB RAM and 192 KiB ROM, basic maths and logical instructions, a fairly mature assembler, basic yet performant emulator written in C++ and much more.

This project is thoroughly documented. You can read the docs here.

The CPU also uses an own instruction set architecture. Key features are:

• support for 8-bit immediates in every ALU instruction:

  add r0, r1, #3
  lshift r2, #2, r3
  

• encapsulated operations, so you can calculate two things at once and apply modifications to your ALU operands:

  sub r4 (add r2 r3) r1
  nand r5 r1 (not r0)
  

• 3-bit immediates in all of said encapsulated operations:

  nor r1 (sub r7 #5) r6
  

• fixed instruction length of 24 bits
• LDI command to immediately load any arbitrary 16-bit value

The assembler tries to make coding as comfortable as possible:

• performs preprocessing and optimization
• it uses a custom assembly language that supports...
  • register notation with either digits (r0, r2, ...) or letters (ra, rc, ...)
  • named jumps and code blocks
  • pre-processor directives such as scoped define statements which allow you to use named registers and constants
  • comments
• detailed errors (with line numbers and descriptions) are thrown once problems are detected

You can find the assembler in the respective folder, asm. It is written in Python. To use an example program, assemble it and copy the entire content of the .hex file, then paste it into the ROM inside of Logisim Evolution (or try out the emulator). The source for these programs is inside of the asm/programs folder.

A command to assemble into all possible output formats, using debug output and optimizations could look like this:

./jcasm ./asm/programs/fibonacci.asm -o ./asm/build/fibonacci.out -dO -f bBrx

The emulator can be found in emu. It is written in C++. As of right now, only files exported from the assembler in the raw ROM format can be used. This is how it can be used:

./jcemu ./asm/build/fibonacci.out

Have fun with it!