KnightOS is an open-source operating system for TI calculators. It is not an OS in the sense that “MirageOS” is, but it is actually a full-blown Operating System that completely replaces TI-OS on your calculator. KnightOS gives you a lot of flexibility. Anyone who’s familiar with Unix-like systems will feel right at home with KnightOS. It’s modular, open source, and powerful.
Let’s take a quick moment to make sure you understand what it means for KnightOS to be open source. It’s rare for projects in the TI community to be truly open-source, and this is an extremely important part of why KnightOS exists and how it’s built. The most obvious point to note about open source is that you are freely able to get and modify the source code of KnightOS. The kernel, all userspace applications, and the entire toolchain is open source. KnightOS uses the MIT/X11 license, which allows you a great deal of freedom when playing with the system.
More importantly, though, is the fact that you are able to share your improvements with KnightOS, and they will be included in future versions of the system. It takes a lot of effort to build such a complex and intricate system like KnightOS, and it’s only done as a result of the combined efforts of lots of contributors. KnightOS is not built by an individual - it’s built by a team. If you’re interested in helping out, please feel free to do so. The system is only as great as it is now because of the help of people like you.
You may have heard that KnightOS is “unix-like”. This is true. Unix is the operating system that defines modern operating systems. Many systems, including Linux and OS X, are based on the ideas Unix brought forth. Following suit, KnightOS takes a lot of ideas from Unix and implements them for calculators. However, KnightOS is only Unix-like. KnightOS does not provide a POSIX runtime and no Unix software is directly compatible with KnightOS.
KnightOS lets you run up to 32 programs at once. You can effortlessly switch between doing math and editing a program without losing your stride. Your programs can also run tasks in the background while your user is busy doing something else. Multitasking on KnightOS is preemptive, meaning that all programs are included by default (and do not have to opt-in or think much about it). Using KnightOS is similar to how you might use a smart phone. You can “suspend” programs in the background, switch to another, and go back and forth as you please. Unlike smartphones, however, programs are offered a full multitasking enviornment, and are allowed to run tasks in the background and create new threads.
On TI-OS, you may be used to placing interesting data in “safe RAM”. There is no such concept on KnightOS. Instead, you tell the system how much memory you need and it sets aside some for you. This allows you to work with up to 31K of continuous memory - far more than you ever get on TI-OS. To make things easier, you are also permitted to set aside space in your programs for non-dynamic memory. More on this subject is discussed in later articles.
Unix has a filesystem standard called the Filesystem Hierarchy
Standard. KnightOS
is a single-user operating system, so it does not follow this exactly.
However, it does draw a lot of inspiration from this standard. On KnightOS,
programs are found in /bin, and variable data is in /var. Libraries go in
/lib, and configuration files in /etc, and so on.
If you hadn’t already gathered, KnightOS has a proper filesystem. Unlike TI-OS’s archive, KnightOS gives you a directory tree and a filesystem like your computer has. This is all stored in Flash - absolutely no user data is stored in RAM. This frees up RAM for your own use, but also prevents crashes from being destructive. Any time your program crashes, no user data will be lost. No more panicked RAM clears!
There is an important distinction on KnightOS between what is in the “kernel” and what is in “userspace” (sometimes called “userland”). The kernel is the most complicated and detailed part of KnightOS, but it doesn’t do anything on its own. The KnightOS kernel resides on pages 0x00 to 0x03 in Flash, and offers most of the foundation of the system. The kernel is responsible for multitasking, memory management, hardware drivers, filesystem access, and so on. However, it rarely interacts with the user directly. It just sits there quietly and does all the hard work for KnightOS.
The userspace, however, consists of all the software you interact with. Userspace
programs are stored on the filesystem in /bin and are loaded into RAM to be
executed when you are using the calculator. For example, the castle and the file
manager are both userspace programs - just like the ones you might write. The
castle resides in /bin/castle and the file manager is in /bin/fileman. As a
general rule, anything that directly interacts with the user is in the userspace.
Other things considered to be in “userspace” include any installed libraries.
The final point we’ll address is the notion of modularity. Most of the programs in userspace do not depend on each other. The only thing neccessary to have a KnightOS system is the kernel - you could remove the castle, the file manager, the settings editor, and everything else, and it’d still be KnightOS. You can do more than remove the things you don’t want - you can replace them. KnightOS is designed in a way that allows you to replace core parts of the OS with any alternative you like. You could write an alternative file manager and install it in place of fileman, and everything would work great. You could use a different launcher than the Castle if you please. You can completely customize your installation of KnightOS and everything will work great.
At this point, you can probably dive into programming on KnightOS. You will probably want to start with the userspace programming guide. If you have any questions, please feel free to visit us on IRC.