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.


So far drivers must be written either using plain in and out instructions or on top of the existing PCI driver.

PCI Device Drivers

PCI device drivers must register a struct pci_device_driver in order to interface with a certain device (or class of devices). See include/kernel/dri/pci/pci.h for details.

A PCI device driver must pass an instance of this structure to pci_register_device_driver (in include/kernel/dri/pci/pci.h. If supports returns true, (for example, if the class and subclass of the struct pci_device are supported by teh driver) init will be called. At this point the driver may do whatever it wishes with the PCI device, although all blocking operations should be done in another thread (using spawn_thread in include/kernel/task.h for example).