SplitBit is a custom CPU designed for hobbyist projects and experimentation. The SplitBit Emulator is a C implementation of its bespoke instruction set architecture. It allows users to load and run binary programs created for the SplitBit CPU interactively from the command line.

Features:

8-bit Harvard Architecture: The system memory is separated into two 64k banks, one for the Program Memory and another for the Data Memory.
Custom ISA: A fully implemented instruction set architecture optimized for simplicity and easy assembly programming.
Debug Mode: Single-step through instructions and monitor the CPU's registers as they change through each cycle.
CLI Based: Debug messages and CPU input and output are supported through the command line.
Binary File Support: Load programs and data from binary files.
Modular Codebase: Mostly clean separation of CPU, I/O, and utility functions for easy modification.
Assembler: Assemble human readable assembly language files directly into SplitBit compatible binary files. Supports including external files, handling labels, and defining Program and Data segments.

Installation:

Clone the repository:

git clone https://github.com/RealBusinessAccount/SplitBit-Emulator.git
cd SplitBit-Emulator

Build the Emulator and the Assembler: You'll need gcc and make or similar.

make

Assemble a program:

./Assembler Programs/hello.asm

Run the program:

./SplitBit hello.bin

Usage:

./SplitBit [options] [binary file]

Options:

-d, --debug: Enable debug mode to single step through cycles. Each keypress advances one instruction.
-c, --cycles N: Stop after N cycles rather than running until the program halts. Useful for programs that never halt, and for getting the same output from a run every time.
-f, --fast: Run as fast as the host machine allows, ignoring the emulated cycle rate.
-h, --help: Show help and usage information.

Usage:

./Assembler [options] [assembly file]

Options:

-o <file>: Write the binary to this path.
-I <dir>: Look in this directory for included files. May be given more than once.
-M <file>: Write out which source files the binary depends on, as a make rule.
-h, --help: Show help and usage information.

Notes:

Without -o, the assembled binary is saved with the same name as the assembly source file, with a .bin extension, in the directory that you call the assembler from.
Included files are looked for beside the file that includes them, and then along the directories given with -I.

Building Programs With Make:

The assembler is built to work with make. The -o option puts the binary where the build system wants it, and -M writes out which libraries went into it, so that editing a library reassembles everything that includes it.

Programs/makefile does this for the programs in this repository:

cd Programs
make

The rule it uses is small enough to copy into your own projects:

$(BUILD)/%.bin: %.asm
	@mkdir -p $(@D)
	$(ASM) -I Libraries -M $(@:.bin=.d) -o $@ $<

-include $(BINARIES:.bin=.d)

Tests:

The test suite assembles and runs every program in Programs/ and compares the results against recorded output.

make test

Tests are defined in Tests/manifest, one line per program. To record the current output as the expected result, after you have checked that it is correct:

make bless

Programs are built inside Tests/build, so running the suite never overwrites the binaries in Programs/. To run only some of the tests, call the runner directly with their names:

./Tests/run.sh hello 8bitFibonacci

Additional Info:

For more information on the custom ISA and programming for SplitBit, see the Programming Manual and Assembler Manual.

License:

This project is licensed under the Apache License, Version 2.0. You may obtain a copy of the License at http://www.apache.org/licenses/LICENSE-2.0.