Zepto text editor

Presenting Zepto: A clone of nano entirely written in Z80 assembly, for Zeal 8-bit OS

About Zepto

The goal of Zepto is to provide a text editor for Zeal 8-bit OS that is complete enough to write some code of text files, without taking too much disk space. This is why I decided to make a clone of the famous nano text editor present on Linux. The problem is nano is written in C and is tied to the libC and Linux kernel. As such, I decided to write a clone from scratch, in Z80 assembly, to minimize the space and time it will take.

Thus, nano was only used as a source of inspiration, its code was not used at all in this project.

Features and limitations

Zepto is still in alpha, here are the features implemented:

• Less than 4KB once compiled!
• Use Zeal 8-bit OS cursor and keyboard API, so completely portable
• Use Gap Buffer data structure to avoid line length limitation
• Use Controller-Model-View architecture
• Open an existing file given as a parameter
• Edit the file content, can split lines, can add characters at the beginning, at the middle and at the end of lines
• Support upper, lower case and special characters
• Support scrolling up and down in the file
• Support Ctrl + Key for menu selection
• Support Location option
• Support Save file option
• Support Exit option
• Support "Save file on exit" question

Regarding the current limitations:

• Screen size is hardcoded to 80x40 characters. In the future, it should use Zeal 8-bit OS video API to get the screen area size
• Doesn't support memory paging, so the maximum file size is limited by the amount of RAM mapped at once: around 40KB
• No way to remove an empty line. Once a new line is created, it cannot be removed, it'll always be in the file
• It is not possible to modify the file destination once the file is opened. For example, if the file B:/file.txt is opened, it is not possible to save it under a new name
• Copy/Paste/Cut/Help/Open File/New File are not implemented

Building the project

Requirements

At the moment, the project has only been assembled on Linux (Ubuntu 20.04 and 22.04), it should be compatible with Mac OS and Windows as long as you have:

• bash
• git (to clone this repo)
• make
• Zeal 8-bit OS source code. Only the kernel_headers directory is required
• Zeal 8-bit OS v0.3.0 or above on the target computer. The older versions don't implement cursor and video APIs
• z88dk v2.2 (or later). Only its assembler, z80asm, is strictly required. The latest version of z80asm must be used as earlier versions don't have support for MACRO.

To install z88dk, please check out their Github project.

Building

To build the program, define the path to Zeal 8-bit OS, this will let us find the header files used to assemble zepto:

export ZOS_PATH=/your/path/to/Zeal8bitOS

Then simply use the command:

make

After compiling, the folder bin/ should contain the binary zepto.bin. This file can be then loaded to Zeal 8-bit OS through UART thanks to the load command.

The binary can also be embedded within the romdisk that will contain both the OS and a read-only file system. For example:

cd $ZOS_PATH
export EXTRA_ROMDISK_FILES="/path/to/zepto/bin/zepto.bin"
make

More info about compiling Zeal 8-bit OS here.

The resulted ROM image can then be provided to an emulator or directly flashed to the computer's ROM that will use it.

Usage

If you are using Zeal 8-bit OS default romdisk, you can use exec command to execute zepto.bin or directly use ./, followed by the source/destination file:

A:/>exec zepto.bin B:/your_file.txt

or

A:/>./zepto.bin B:/your_file.txt

As said above, keep in mind that once opened, the file cannot be renamed or saved somewhere else, so make sure you specify a destination disk that is write-read! (A:/ disk isn't by default)

Contact

For any suggestion or request, you can contact me at contact [at] zeal8bit [dot] com

Or, you can join Zeal 8-bit projects Discord server.

For features requests, you can also open an issue or a pull request.

Contributing

Contributions are welcome! Feel free to fix any bug that you may see or encounter, or implement any feature that you find important.

To contribute:

• Fork the Project
• Create your feature Branch (optional)
• Commit your changes. Please make a clear and concise commit message (*)
• Push to the branch
• Open a Pull Request

(*) A good commit message is as follow:

Module: add/fix/remove a from b

Explanation on what/how/why

For example:

Flash: add the possibility to flash programs bigger than 48KB

License

Distributed under the Apache 2.0 License. See LICENSE file for more information.

You are free to use it for personal and commercial use, the boilerplate present in each file must not be removed.