| Architecture |
| ============ |
| |
| This document seeks to provide a brief overview of Bluejay architecture. This |
| should be a good starting point for understanding the code. |
| |
| Bluejay is exclusively a multiboot kernel, it neither provides nor supports |
| alternative bootloaders. |
| |
| The bootloader (probably GRUB) will initially run the code in ``boot.s``. This |
| is where it all begins. This code sets up segmentation and paging and maps the |
| higher-half of virtual memory (everything above ``0xC0000000``) to the kernel. |
| At first it only maps 8 megabytes, more memory can be mapped on request. |
| |
| After moving to high memory the kernel jumps to C code and enters ``kmain`` in |
| ``main.c``. This is the highest level procedure in the kernel, which sets up |
| kernel services and drivers one at a time. |
| |
| This includes VGA, keyboard, and PCI drivers, as well as paging and preemptive |
| multi tasking. |
| |
| Multi tasking |
| ------------- |
| |
| Multi tasking is handled by code in ``task.c``. It is first initialized in |
| ``init_tasks``, which sets up the initial task. Once this is called kernel |
| threads can be spawned at will. |
| |
| Every clock tick an interrupt is triggered (see ``clock.c`` for timing) which |
| causes a task switch to occur. Bluejay uses a simple round-robin scheduler, and |
| there is no way for tasks to voluntarily give up their processing time (even in |
| the case of blocking IO operations). ``task.c`` contains the implementation of |
| the scheduler. |
| |
| Drivers |
| ------- |
| |
| So far I have only written very low level drivers (stuff like ATA PIO, PCI, VGA |
| text mode, etc). These drivers have all been "bare-metal", ie: interfacing with |
| hardware through ``in`` and ``out`` instructions. Higher level drivers will be |
| built on top of existing ones. An interface will be created for defining, for |
| example, PCI device drivers, or USB device drivers. |