Code Wrangling at its Best
In Chapter 14, we added the first interactive kernel monitor: That worked, but the monitor command parser was still a chain of if statements: That is fine for five commands, but it does not scale. This chapter cleans that up by adding: The keyboard improvement matters because our monitor is interactive now. A monitor where
Continue Reading “Chapter 15 — Command Tables, Argument Parsing, and Shift-Aware Keyboard Input”
At this point our kernel has enough machinery to become interactive: Now we will build two new layers: The terminal line discipline turns raw keyboard characters into editable input lines. It handles: The kernel monitor is a small command loop: This is not user space yet. It is still a kernel thread. But it gives
Continue Reading “Chapter 14 — Terminal Line Discipline and a Kernel Monitor”
In Chapter 12, we added wait queues and blocking keyboard input: Now we need synchronization primitives that ordinary kernel code can use. This chapter adds: A mutex provides mutual exclusion: only one thread may hold the protected resource at a time. OSDev describes a mutex as a mutual-exclusion mechanism, similar to a binary semaphore, used
Continue Reading “Chapter 13 — Mutexes, Semaphores, and a Console Lock”
In Chapter 11, we added the first blocking primitive: That gave the scheduler a way to remove a thread from the ready queue until a future timer tick. Now we need a more general primitive: This is the foundation for real kernel I/O. A keyboard reader should not spin like this: It should block: This
Continue Reading “Chapter 12 – Wait Queues and Blocking Keyboard Input”
In Chapter 10, we added timer-driven preemption: Now we need the next scheduler capability: blocking. A runnable thread competes for CPU time. A blocked or sleeping thread does not. OSDev describes a blocking process as one that waits for an event, such as a semaphore or message, and is removed from the active scheduling queue
Continue Reading “Chapter 11 — Blocking Primitives, Sleep Queues, and Scheduler Hygiene”
In Chapter 9, we built cooperative multitasking: That works, but it has a major weakness: A thread like that can monopolize the CPU forever. This chapter adds the next step: timer-driven preemption. With preemptive scheduling: OSDev describes preemptive multitasking as scheduling where an interrupt, usually timer-driven, allows the kernel to take control away from the
Continue Reading “Chapter 10 — Timer-Driven Preemptive Multitasking”
We now have enough foundation to start multitasking: This chapter adds the first scheduler. Not a preemptive scheduler yet. A cooperative scheduler. That means each kernel thread keeps running until it voluntarily calls: “` cthread_yield(); textkernel thread objectper-thread kernel stackready queuex86 context switch assemblythread_create()thread_yield()thread_exit()round-robin cooperative schedulingtwo-thread test textcreate two kernel threadsswitch between them cooperativelyprove both
Continue Reading “Chapter 9 — Cooperative Multitasking and Kernel Threads”
In Chapter 6, the kernel heap still depended on low identity-mapped physical pages. That worked as a bootstrap step, but it tied the heap to the first 16 MiB of RAM. In Chapter 7, we added a real VMM and proved that the kernel can map and unmap pages anywhere the page tables allow. That
Continue Reading “Chapter 8 – Moving the Heap onto Virtual Memory”
In Chapter 5, we enabled paging with a simple identity map: That gave us a working paged kernel, but not yet a comfortable way to allocate variable-sized objects. The physical memory manager gives us whole pages: But kernel code usually needs smaller objects: So this chapter builds the first kernel heap. We will keep it
Continue Reading “Chapter 6 — Building the First Kernel Heap”
In Chapter 4, we built the first memory-management layer: Now we add the next layer: paging. Paging lets the CPU translate a virtual address into a physical address through page tables. In 32-bit x86 paging without PAE, a virtual address is split into a page-directory index, page-table index, and page offset; page directories and page
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