4 * This file is part of BeRTOS.
6 * Bertos is free software; you can redistribute it and/or modify
7 * it under the terms of the GNU General Public License as published by
8 * the Free Software Foundation; either version 2 of the License, or
9 * (at your option) any later version.
11 * This program is distributed in the hope that it will be useful,
12 * but WITHOUT ANY WARRANTY; without even the implied warranty of
13 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 * GNU General Public License for more details.
16 * You should have received a copy of the GNU General Public License
17 * along with this program; if not, write to the Free Software
18 * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
20 * As a special exception, you may use this file as part of a free software
21 * library without restriction. Specifically, if other files instantiate
22 * templates or use macros or inline functions from this file, or you compile
23 * this file and link it with other files to produce an executable, this
24 * file does not by itself cause the resulting executable to be covered by
25 * the GNU General Public License. This exception does not however
26 * invalidate any other reasons why the executable file might be covered by
27 * the GNU General Public License.
29 * Copyright 2001,2004 Develer S.r.l. (http://www.develer.com/)
30 * Copyright 1999,2000,2001 Bernardo Innocenti <bernie@develer.com>
34 * \brief Simple realtime multitasking scheduler.
35 * Context switching is only done cooperatively.
39 * \author Bernardo Innocenti <bernie@develer.com>
40 * \author Stefano Fedrigo <aleph@develer.com>
47 #include <mware/event.h>
49 #include <cpu/types.h>
51 #include <cfg/debug.h>
52 #include <cfg/module.h>
53 #include <cfg/arch_config.h> /* ARCH_EMUL */
54 #include <cfg/macros.h> /* ABS() */
56 #include <string.h> /* memset() */
59 * CPU dependent context switching routines.
61 * \note This function *MUST* preserve also the status of the interrupts.
63 EXTERN_C void asm_switch_context(cpustack_t **new_sp, cpustack_t **save_sp);
64 EXTERN_C int asm_switch_version(void);
67 * The scheduer tracks ready and waiting processes
68 * by enqueuing them in these lists. A pointer to the currently
69 * running process is stored in the CurrentProcess pointer.
71 * NOTE: these variables are protected by DI/EI locking
73 REGISTER Process *CurrentProcess;
74 REGISTER List ProcReadyList;
77 #if CONFIG_KERN_PREEMPTIVE
79 * The time sharing scheduler forces a task switch when
80 * the current process has consumed its quantum.
86 /* In Win32 we must emulate stack on the real process stack */
87 #if (ARCH & ARCH_EMUL)
88 extern List StackFreeList;
91 /** The main process (the one that executes main()). */
92 struct Process MainProcess;
95 static void proc_init_struct(Process *proc)
97 /* Avoid warning for unused argument. */
100 #if CONFIG_KERN_SIGNALS
104 #if CONFIG_KERN_PREEMPTIVE
105 proc->forbid_cnt = 0;
117 LIST_INIT(&ProcReadyList);
119 #if CONFIG_KERN_MONITOR
123 /* We "promote" the current context into a real process. The only thing we have
124 * to do is create a PCB and make it current. We don't need to setup the stack
125 * pointer because it will be written the first time we switch to another process.
127 proc_init_struct(&MainProcess);
128 CurrentProcess = &MainProcess;
130 /* Make sure the assembly routine is up-to-date with us */
131 ASSERT(asm_switch_version() == 1);
137 * Create a new process, starting at the provided entry point.
139 * \return Process structure of new created process
140 * if successful, NULL otherwise.
142 struct Process *proc_new_with_name(UNUSED(const char *, name), void (*entry)(void), iptr_t data, size_t stacksize, cpustack_t *stack_base)
146 size_t proc_size_words = ROUND2(sizeof(Process), sizeof(cpustack_t)) / sizeof(cpustack_t);
148 bool free_stack = false;
151 #if (ARCH & ARCH_EMUL)
152 /* Ignore stack provided by caller and use the large enough default instead. */
153 stack_base = (cpustack_t *)LIST_HEAD(&StackFreeList);
154 REMOVE(LIST_HEAD(&StackFreeList));
155 stacksize = CONFIG_PROC_DEFSTACKSIZE;
156 #elif CONFIG_KERN_HEAP
157 /* Did the caller provide a stack for us? */
160 /* Did the caller specify the desired stack size? */
162 stacksize = CONFIG_PROC_DEFSTACKSIZE + sizeof(Process);
164 /* Allocate stack dinamically */
165 if (!(stack_base = heap_alloc(stacksize)))
171 /* Stack must have been provided by the user */
176 #if CONFIG_KERN_MONITOR
177 /* Fill-in the stack with a special marker to help debugging */
178 memset(stack_base, CONFIG_KERN_STACKFILLCODE, stacksize / sizeof(cpustack_t));
181 /* Initialize the process control block */
182 if (CPU_STACK_GROWS_UPWARD)
184 proc = (Process*)stack_base;
185 proc->stack = stack_base + proc_size_words;
186 if (CPU_SP_ON_EMPTY_SLOT)
191 proc = (Process*)(stack_base + stacksize / sizeof(cpustack_t) - proc_size_words);
192 proc->stack = (cpustack_t*)proc;
193 if (CPU_SP_ON_EMPTY_SLOT)
197 proc_init_struct(proc);
198 proc->user_data = data;
201 proc->stack_base = stack_base;
202 proc->stack_size = stack_size;
204 proc->flags |= PF_FREESTACK;
207 /* Initialize process stack frame */
208 CPU_PUSH_CALL_CONTEXT(proc->stack, proc_exit);
209 CPU_PUSH_CALL_CONTEXT(proc->stack, entry);
211 /* Push a clean set of CPU registers for asm_switch_context() */
212 for (i = 0; i < CPU_SAVED_REGS_CNT; i++)
213 CPU_PUSH_WORD(proc->stack, CPU_REG_INIT_VALUE(i));
215 /* Add to ready list */
216 ATOMIC(SCHED_ENQUEUE(proc));
218 #if CONFIG_KERN_MONITOR
219 monitor_add(proc, name, stack_base, stacksize);
225 /** Rename a process */
226 void proc_rename(struct Process *proc, const char *name)
228 #if CONFIG_KERN_MONITOR
229 monitor_rename(proc, name);
231 (void)proc; (void)name;
237 * System scheduler: pass CPU control to the next process in
240 * Saving and restoring the context on the stack is done
241 * by a CPU-dependent support routine which must usually be
242 * written in assembly.
244 void proc_schedule(void)
246 struct Process *old_process;
249 /* Remember old process to save its context later */
250 old_process = CurrentProcess;
253 /* Scheduling in interrupts is a nono. */
254 ASSERT(!IRQ_RUNNING());
257 /* Poll on the ready queue for the first ready process */
258 IRQ_SAVE_DISABLE(flags);
259 while (!(CurrentProcess = (struct Process *)list_remHead(&ProcReadyList)))
262 * Make sure we physically reenable interrupts here, no matter what
263 * the current task status is. This is important because if we
264 * are idle-spinning, we must allow interrupts, otherwise no
265 * process will ever wake up.
267 * During idle-spinning, an interrupt can occur and it may
268 * modify \p ProcReadyList. To ensure that compiler reload this
269 * variable every while cycle we call CPU_MEMORY_BARRIER.
270 * The memory barrier ensure that all variables used in this context
272 * \todo If there was a way to write sig_wait() so that it does not
273 * disable interrupts while waiting, there would not be any
284 * Optimization: don't switch contexts when the active
285 * process has not changed.
287 if (CurrentProcess != old_process)
291 #if CONFIG_KERN_PREEMPTIVE
292 /* Reset quantum for this process */
293 Quantum = CONFIG_KERN_QUANTUM;
296 /* Save context of old process and switch to new process. If there is no
297 * old process, we save the old stack pointer into a dummy variable that
298 * we ignore. In fact, this happens only when the old process has just
300 * TODO: Instead of physically clearing the process at exit time, a zombie
301 * list should be created.
303 asm_switch_context(&CurrentProcess->stack, old_process ? &old_process->stack : &dummy);
306 /* This RET resumes the execution on the new process */
311 * Terminate the current process
315 #if CONFIG_KERN_MONITOR
316 monitor_remove(CurrentProcess);
321 * The following code is BROKEN.
322 * We are freeing our own stack before entering proc_schedule()
323 * BAJO: A correct fix would be to rearrange the scheduler with
324 * an additional parameter which frees the old stack/process
325 * after a context switch.
327 if (CurrentProcess->flags & PF_FREESTACK)
328 heap_free(CurrentProcess->stack_base, CurrentProcess->stack_size);
329 heap_free(CurrentProcess);
332 #if (ARCH & ARCH_EMUL)
333 #warning This is wrong
334 /* Reinsert process stack in free list */
335 ADDHEAD(&StackFreeList, (Node *)(CurrentProcess->stack
336 - (CONFIG_PROC_DEFSTACKSIZE / sizeof(cpustack_t))));
339 * NOTE: At this point the first two words of what used
340 * to be our stack contain a list node. From now on, we
341 * rely on the compiler not reading/writing the stack.
343 #endif /* ARCH_EMUL */
345 CurrentProcess = NULL;
352 * Co-operative context switch
354 void proc_switch(void)
358 IRQ_SAVE_DISABLE(flags);
359 SCHED_ENQUEUE(CurrentProcess);
367 * Get the pointer to the current process
369 struct Process *proc_current(void)
371 return CurrentProcess;
375 * Get the pointer to the user data of the current process
377 iptr_t proc_current_user_data(void)
379 return CurrentProcess->user_data;
383 #if CONFIG_KERN_PREEMPTIVE
386 * Disable preemptive task switching.
388 * The scheduler maintains a per-process nesting counter. Task switching is
389 * effectively re-enabled only when the number of calls to proc_permit()
390 * matches the number of calls to proc_forbid().
392 * Calling functions that could sleep while task switching is disabled
393 * is dangerous, although supported. Preemptive task switching is
394 * resumed while the process is sleeping and disabled again as soon as
399 void proc_forbid(void)
401 /* No need to protect against interrupts here. */
402 ++CurrentProcess->forbid_cnt;
406 * Re-enable preemptive task switching.
410 void proc_permit(void)
412 /* No need to protect against interrupts here. */
413 --CurrentProcess->forbid_cnt;
416 #endif /* CONFIG_KERN_PREEMPTIVE */