niclas3/frog

Purpose and Execution Model

Frog is a self-teaching 32-bit x86 PC operating system: a bootloader loads a kernel that initializes hardware, memory, interrupts, processes, storage, and a desktop compositor. It is built for disk-image boot under QEMU/Bochs rather than hosted execution.

Boot and Kernel Entry

The boot chain begins in the MBR and loader assembly, then transfers into the protected-mode kernel assembly/C entry path. Core startup establishes the low-level runtime before subsystems are available.

• booter/MBR.s

• booter/loader.s

• core/core.s

• core/bootpack.c

CPU Protection, Interrupts, and Time

Descriptor/TSS setup defines x86 protected-mode execution context. PIC and interrupt code route hardware faults and IRQs; the PIT-backed timer drives timing and likely scheduling/timeout activity. Softirqs provide deferred interrupt work.

• core/destab/descriptor.c

• core/destab/tss.c

• core/interrupt/int.c

• core/pic/pic.c

• core/frog/pit8253.c

Process and System-Service Boundary

The thread/process subsystem owns task creation, context switching, scheduling, fork/exec/exit, and synchronization. User-facing syscall initialization and dispatch form the boundary from applications/system tasks into kernel services.

• core/thread/sched.c

• core/thread/process.c

• core/thread/switch.s

• core/usr/syscall-init.c

• core/usr/syscall.c

Memory, IPC, and Kernel Coordination

Physical/virtual memory management underpins process execution. IPC, pipes, semaphores, queues, and select-style readiness are the primary coordination mechanisms between processes and device/service code.

• core/mm/memory.c

• core/ipc/ipc.c

• core/fs/pipe.c

• core/fs/select.c

• core/thread/semaphore.c

Devices, Storage, and Filesystem

Hardware drivers cover CMOS, console, IDE disks, PS/2 keyboard/mouse, and linear-framebuffer video. IDE is the storage boundary; filesystem layers expose directories, files, inodes, and a package filesystem abstraction above it.

• core/device/ide.c

• core/device/pc_kbd.c

• core/device/ps2hid.c

• core/fs/fs.c

• core/vfs/packagefs.c

Graphics and Desktop Stack

Framebuffer video feeds graphics and GUI support libraries. The compositor and desktop applications consume these facilities; image decoders indicate desktop rendering can load BMP/JPEG assets. “Poudland” headers/library suggest an internal display-server/client protocol boundary.

• core/video/lfbvideo.c

• core/apps/compositor.c

• core/apps/desktop.c

• core/lib/poudland.c

• core/lib/2d_graphics.c

Build and Runtime Infrastructure

Makefiles partition bootloader, kernel, devices, filesystem, apps, libraries, and tools. Shell scripts build images and launch/debug QEMU; Bochs configs are also present. Required runtime artifacts are user-created hd.img and hd80M.img disk images. Networking currently exposes a socket-oriented kernel surface but README identifies TCP/IP as unfinished.

• Makefile

• scripts/build.sh

• scripts/qemu.sh

• bochsrc

• core/net/socket.c