391 lines
11 KiB
C
391 lines
11 KiB
C
/*
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* task.c – Cooperative multitasking: PCB pool, scheduler, yield/exit.
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*
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* Task 0 is the always-present kernel core thread (uses the boot stack).
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* Additional tasks are created with task_create(), which allocates a
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* stack from the PMM and sets up a fake context-switch frame so that
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* context_switch() can "return" into a trampoline that calls the real
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* entry function.
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*
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* Scheduling is purely cooperative: tasks must call task_yield() to
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* let others run. The scheduler uses round-robin selection among
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* READY tasks.
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*/
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#include "task.h"
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#include "memory.h"
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/* Null-safe print helper used throughout the kernel. */
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#define SAFE_PRINT(Boot, ...) \
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do { \
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if ((Boot) != NULL && (Boot)->print != NULL) { \
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(Boot)->print(__VA_ARGS__); \
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} \
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} while (0)
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/* ================================================================
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* Module state
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* ================================================================ */
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static Task tasks[TASK_MAX]; /* PCB pool (static array) */
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static Task *current_task = NULL;
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static UINT32 next_pid = 0;
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static BootInfo *task_boot = NULL;
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static BOOLEAN task_ready = FALSE;
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/* Forward declaration */
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static void task_trampoline(void);
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/* ----------------------------------------------------------------
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* Helpers
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* ---------------------------------------------------------------- */
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/* Copy a wide string with a maximum length (including NUL). */
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static void wstrcpy16(CHAR16 *dst, const CHAR16 *src, UINTN max)
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{
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UINTN i = 0;
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while (i < max - 1 && src != NULL && src[i] != L'\0') {
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dst[i] = src[i];
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i++;
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}
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dst[i] = L'\0';
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}
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/* ----------------------------------------------------------------
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* Initialisation – make the current (kernel) thread task 0
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* ---------------------------------------------------------------- */
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/*
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* Initialise the scheduler: clear all PCB slots and register the
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* currently running kernel core thread as task 0.
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*/
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void task_init(BootInfo *Boot)
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{
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UINTN i;
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task_boot = Boot;
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/* Clear all PCB slots */
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for (i = 0; i < TASK_MAX; i++) {
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tasks[i].state = TASK_STATE_FREE;
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tasks[i].pid = 0;
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tasks[i].saved_rsp = 0;
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tasks[i].stack_base = 0;
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tasks[i].stack_pages = 0;
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tasks[i].entry = NULL;
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tasks[i].arg = NULL;
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tasks[i].switches = 0;
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tasks[i].name[0] = L'\0';
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}
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/*
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* Task 0 = the currently running kernel core thread.
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* It already has a stack (the kernel's boot stack), so we don't
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* allocate one. Its saved_rsp will be filled in during the
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* first context_switch call in task_yield().
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*/
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tasks[0].pid = next_pid++;
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tasks[0].state = TASK_STATE_RUNNING;
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tasks[0].switches = 1;
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wstrcpy16(tasks[0].name, L"core", TASK_NAME_LEN);
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current_task = &tasks[0];
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task_ready = TRUE;
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SAFE_PRINT(Boot, L" Tasks: scheduler ready (max %d tasks)\n\r",
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(UINTN)TASK_MAX);
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}
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/* ----------------------------------------------------------------
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* Trampoline – first code a new task executes after context_switch
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* returns into it. It calls the real entry function and then
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* performs a clean task_exit().
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* ---------------------------------------------------------------- */
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static void task_trampoline(void)
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{
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Task *t = task_current();
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if (t != NULL && t->entry != NULL) {
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t->entry(t->arg);
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}
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task_exit();
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/* Should never reach here, but just in case: */
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for (;;) {
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__asm__ __volatile__("hlt");
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}
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}
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/* ----------------------------------------------------------------
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* Create a new task
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* ---------------------------------------------------------------- */
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Task *task_create(const CHAR16 *name, TaskEntryFn entry, void *arg)
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{
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Task *t = NULL;
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UINTN i;
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UINT64 stack_phys;
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UINT64 *sp;
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if (!task_ready || entry == NULL) {
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return NULL;
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}
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/* Find a free PCB slot */
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for (i = 0; i < TASK_MAX; i++) {
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if (tasks[i].state == TASK_STATE_FREE) {
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t = &tasks[i];
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break;
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}
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}
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if (t == NULL) {
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return NULL; /* out of slots */
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}
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/* Allocate stack pages from the physical memory manager */
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stack_phys = pmm_alloc_pages(TASK_STACK_PAGES);
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if (stack_phys == 0) {
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return NULL; /* out of memory */
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}
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/* Fill in the PCB */
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t->pid = next_pid++;
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t->state = TASK_STATE_READY;
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t->entry = entry;
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t->arg = arg;
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t->switches = 0;
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t->stack_base = stack_phys;
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t->stack_pages = TASK_STACK_PAGES;
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wstrcpy16(t->name, name != NULL ? name : L"unnamed", TASK_NAME_LEN);
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/*
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* Set up the initial stack frame so that context_switch() can
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* "return" into task_trampoline().
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*
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* context_switch saves/restores (low → high on stack):
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* flags, r15, r14, r13, r12, rbx, rbp (pushes)
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* then `ret` pops the return address (→ trampoline)
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*
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* Above the return address we place a safety-net address
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* (task_exit) so that if the trampoline or entry function does
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* a bare `ret`, it lands in task_exit().
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*/
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sp = (UINT64 *)(stack_phys + TASK_STACK_SIZE);
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/* Align stack top to 16 bytes */
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sp = (UINT64 *)((UINT64)sp & ~0xFULL);
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/* Safety-net return address for the trampoline */
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*(--sp) = (UINT64)(UINTN)task_exit;
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/* Return address for context_switch's `ret` → trampoline */
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*(--sp) = (UINT64)(UINTN)task_trampoline;
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/* Callee-saved registers – all zero for fresh task */
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*(--sp) = 0; /* rbp */
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*(--sp) = 0; /* rbx */
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*(--sp) = 0; /* r12 */
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*(--sp) = 0; /* r13 */
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*(--sp) = 0; /* r14 */
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*(--sp) = 0; /* r15 */
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/* RFLAGS – interrupts enabled (IF = bit 9) */
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*(--sp) = 0x202; /* flags */
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t->saved_rsp = (UINT64)(UINTN)sp;
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return t;
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}
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/* ----------------------------------------------------------------
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* Schedule – pick the next READY task (round-robin)
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* ---------------------------------------------------------------- */
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static Task *schedule_next(void)
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{
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UINTN start, idx, i;
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if (current_task == NULL) {
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return &tasks[0];
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}
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/* Find current task's index in the array */
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start = (UINTN)(current_task - tasks);
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/* Round-robin: scan from (current+1) wrapping around */
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for (i = 1; i <= TASK_MAX; i++) {
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idx = (start + i) % TASK_MAX;
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if (tasks[idx].state == TASK_STATE_READY) {
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return &tasks[idx];
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}
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}
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/* No other ready task – stay with current if still runnable */
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if (current_task->state == TASK_STATE_RUNNING ||
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current_task->state == TASK_STATE_READY) {
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return current_task;
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}
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/* Fallback to task 0 (kernel / shell) */
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return &tasks[0];
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}
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/* ----------------------------------------------------------------
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* Yield – voluntarily give up the CPU to the next ready task
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* ---------------------------------------------------------------- */
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void task_yield(void)
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{
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Task *prev, *next;
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if (!task_ready) {
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return;
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}
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prev = current_task;
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next = schedule_next();
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if (next == prev) {
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return; /* nothing else to switch to */
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}
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/* Mark the previous task as READY (still runnable) */
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if (prev->state == TASK_STATE_RUNNING) {
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prev->state = TASK_STATE_READY;
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}
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next->state = TASK_STATE_RUNNING;
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next->switches++;
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current_task = next;
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/*
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* context_switch saves callee-saved regs + flags on prev's stack,
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* stores prev's RSP into prev->saved_rsp, loads next->saved_rsp
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* into RSP, restores regs + flags, and `ret`s into next's code.
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*/
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context_switch(&prev->saved_rsp, next->saved_rsp);
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}
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/* ----------------------------------------------------------------
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* Exit – terminate the current task and switch away
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* ---------------------------------------------------------------- */
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void task_exit(void)
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{
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Task *prev, *next;
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if (!task_ready) {
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return;
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}
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prev = current_task;
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prev->state = TASK_STATE_TERMINATED;
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/* Free the stack memory back to the PMM */
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if (prev->stack_base != 0 && prev->stack_pages != 0) {
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pmm_free_pages(prev->stack_base, prev->stack_pages);
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prev->stack_base = 0;
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prev->stack_pages = 0;
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}
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/* Mark the PCB slot as free for reuse */
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prev->state = TASK_STATE_FREE;
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next = schedule_next();
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if (next == prev) {
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/* Shouldn't happen if task 0 (kernel) is always alive */
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next = &tasks[0];
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}
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next->state = TASK_STATE_RUNNING;
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next->switches++;
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current_task = next;
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/* One-way switch: we never return to the exited task */
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context_switch(&prev->saved_rsp, next->saved_rsp);
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/* Should never reach here */
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for (;;) {
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__asm__ __volatile__("hlt");
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}
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}
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/* ----------------------------------------------------------------
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* Accessors
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* ---------------------------------------------------------------- */
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Task *task_current(void)
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{
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return current_task;
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}
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UINTN task_count(void)
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{
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UINTN i, count = 0;
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for (i = 0; i < TASK_MAX; i++) {
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if (tasks[i].state != TASK_STATE_FREE) {
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count++;
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}
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}
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return count;
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}
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/* ----------------------------------------------------------------
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* Wait for another task to finish
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* ---------------------------------------------------------------- */
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void task_wait(Task *t)
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{
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if (!task_ready || t == NULL) {
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return;
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}
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/*
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* Busy-wait cooperatively until the target task's PCB slot has
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* been recycled back to FREE by task_exit().
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*/
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while (t->state != TASK_STATE_FREE) {
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task_yield();
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}
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}
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/* ----------------------------------------------------------------
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* Print task list (implements the `ps` command)
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* ---------------------------------------------------------------- */
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static const CHAR16 *state_str(TaskState s)
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{
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switch (s) {
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case TASK_STATE_FREE: return L"FREE";
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case TASK_STATE_READY: return L"READY";
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case TASK_STATE_RUNNING: return L"RUNNING";
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case TASK_STATE_TERMINATED: return L"ENDED";
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default: return L"???";
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}
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}
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void task_print_list(BootInfo *Boot)
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{
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UINTN i;
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SAFE_PRINT(Boot, L"\n\r");
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SAFE_PRINT(Boot, L" PID STATE SWITCHES NAME\n\r");
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SAFE_PRINT(Boot, L" --- ---------- -------- ----\n\r");
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for (i = 0; i < TASK_MAX; i++) {
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if (tasks[i].state == TASK_STATE_FREE) {
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continue;
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}
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SAFE_PRINT(Boot, L" %3d %-10s %8d %s\n\r",
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tasks[i].pid,
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state_str(tasks[i].state),
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tasks[i].switches,
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tasks[i].name);
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}
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SAFE_PRINT(Boot, L"\n\r");
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SAFE_PRINT(Boot, L" Active tasks: %d / %d\n\r",
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task_count(), (UINTN)TASK_MAX);
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SAFE_PRINT(Boot, L"\n\r");
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}
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