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 Bernie Innocenti <bernie@codewiz.org>
34 * \brief Simple realtime multitasking scheduler.
35 * Context switching is only done cooperatively.
39 * \author Bernie Innocenti <bernie@codewiz.org>
40 * \author Stefano Fedrigo <aleph@develer.com>
47 #include "cfg/cfg_arch.h" /* ARCH_EMUL */
48 #include <cfg/debug.h>
49 #include <cfg/module.h>
50 #include <cfg/macros.h> /* ABS() */
53 #include <cpu/types.h>
56 #include <mware/event.h>
58 #include <string.h> /* memset() */
61 * CPU dependent context switching routines.
63 * \note This function *MUST* preserve also the status of the interrupts.
65 EXTERN_C void asm_switch_context(cpustack_t **new_sp, cpustack_t **save_sp);
68 * The scheduer tracks ready and waiting processes
69 * by enqueuing them in these lists. A pointer to the currently
70 * running process is stored in the CurrentProcess pointer.
72 * NOTE: these variables are protected by DI/EI locking
74 REGISTER Process *CurrentProcess;
75 REGISTER List ProcReadyList;
78 #if CONFIG_KERN_PREEMPTIVE
80 * The time sharing scheduler forces a task switch when
81 * the current process has consumed its quantum.
87 /* In Win32 we must emulate stack on the real process stack */
88 #if (ARCH & ARCH_EMUL)
89 extern List StackFreeList;
92 /** The main process (the one that executes main()). */
93 struct Process MainProcess;
96 static void proc_init_struct(Process *proc)
98 /* Avoid warning for unused argument. */
101 #if CONFIG_KERN_SIGNALS
105 #if CONFIG_KERN_PREEMPTIVE
106 proc->forbid_cnt = 0;
118 LIST_INIT(&ProcReadyList);
120 #if CONFIG_KERN_MONITOR
124 /* We "promote" the current context into a real process. The only thing we have
125 * to do is create a PCB and make it current. We don't need to setup the stack
126 * pointer because it will be written the first time we switch to another process.
128 proc_init_struct(&MainProcess);
129 CurrentProcess = &MainProcess;
136 * Create a new process, starting at the provided entry point.
138 * \return Process structure of new created process
139 * if successful, NULL otherwise.
141 struct Process *proc_new_with_name(UNUSED(const char *, name), void (*entry)(void), iptr_t data, size_t stack_size, cpustack_t *stack_base)
145 const size_t PROC_SIZE_WORDS = ROUND2(sizeof(Process), sizeof(cpustack_t)) / sizeof(cpustack_t);
147 bool free_stack = false;
150 #if (ARCH & ARCH_EMUL)
151 /* Ignore stack provided by caller and use the large enough default instead. */
152 stack_base = (cpustack_t *)list_remHead(&StackFreeList);
154 stack_size = CONFIG_PROC_DEFSTACKSIZE;
155 #elif CONFIG_KERN_HEAP
156 /* Did the caller provide a stack for us? */
159 /* Did the caller specify the desired stack size? */
161 stack_size = CONFIG_PROC_DEFSTACKSIZE + sizeof(Process);
163 /* Allocate stack dinamically */
164 if (!(stack_base = heap_alloc(stack_size)))
170 /* Stack must have been provided by the user */
175 #if CONFIG_KERN_MONITOR
176 /* Fill-in the stack with a special marker to help debugging */
177 memset(stack_base, CONFIG_KERN_STACKFILLCODE, stack_size / sizeof(cpustack_t));
180 /* Initialize the process control block */
181 if (CPU_STACK_GROWS_UPWARD)
183 proc = (Process*)stack_base;
184 proc->stack = stack_base + PROC_SIZE_WORDS;
185 if (CPU_SP_ON_EMPTY_SLOT)
190 proc = (Process*)(stack_base + stack_size / sizeof(cpustack_t) - PROC_SIZE_WORDS);
191 proc->stack = (cpustack_t*)proc;
192 if (CPU_SP_ON_EMPTY_SLOT)
196 proc_init_struct(proc);
197 proc->user_data = data;
199 #if CONFIG_KERN_HEAP | CONFIG_KERN_MONITOR | (ARCH & ARCH_EMUL)
200 proc->stack_base = stack_base;
201 proc->stack_size = stack_size;
204 proc->flags |= PF_FREESTACK;
208 /* Initialize process stack frame */
209 CPU_PUSH_CALL_CONTEXT(proc->stack, proc_exit);
210 CPU_PUSH_CALL_CONTEXT(proc->stack, entry);
212 /* Push a clean set of CPU registers for asm_switch_context() */
213 for (i = 0; i < CPU_SAVED_REGS_CNT; i++)
214 CPU_PUSH_WORD(proc->stack, CPU_REG_INIT_VALUE(i));
216 /* Add to ready list */
217 ATOMIC(SCHED_ENQUEUE(proc));
219 #if CONFIG_KERN_MONITOR
220 monitor_add(proc, name);
226 /** Rename a process */
227 void proc_rename(struct Process *proc, const char *name)
229 #if CONFIG_KERN_MONITOR
230 monitor_rename(proc, name);
232 (void)proc; (void)name;
238 * System scheduler: pass CPU control to the next process in
241 * Saving and restoring the context on the stack is done
242 * by a CPU-dependent support routine which must usually be
243 * written in assembly.
245 void proc_schedule(void)
247 struct Process *old_process;
250 /* Remember old process to save its context later */
251 old_process = CurrentProcess;
254 /* Scheduling in interrupts is a nono. */
255 ASSERT(!IRQ_RUNNING());
258 /* Poll on the ready queue for the first ready process */
259 IRQ_SAVE_DISABLE(flags);
260 while (!(CurrentProcess = (struct Process *)list_remHead(&ProcReadyList)))
263 * Make sure we physically reenable interrupts here, no matter what
264 * the current task status is. This is important because if we
265 * are idle-spinning, we must allow interrupts, otherwise no
266 * process will ever wake up.
268 * During idle-spinning, an interrupt can occur and it may
269 * modify \p ProcReadyList. To ensure that compiler reload this
270 * variable every while cycle we call CPU_MEMORY_BARRIER.
271 * The memory barrier ensure that all variables used in this context
273 * \todo If there was a way to write sig_wait() so that it does not
274 * disable interrupts while waiting, there would not be any
285 * Optimization: don't switch contexts when the active
286 * process has not changed.
288 if (CurrentProcess != old_process)
292 #if CONFIG_KERN_PREEMPTIVE
293 /* Reset quantum for this process */
294 Quantum = CONFIG_KERN_QUANTUM;
297 /* Save context of old process and switch to new process. If there is no
298 * old process, we save the old stack pointer into a dummy variable that
299 * we ignore. In fact, this happens only when the old process has just
301 * TODO: Instead of physically clearing the process at exit time, a zombie
302 * list should be created.
304 asm_switch_context(&CurrentProcess->stack, old_process ? &old_process->stack : &dummy);
307 /* This RET resumes the execution on the new process */
312 * Terminate the current process
316 #if CONFIG_KERN_MONITOR
317 monitor_remove(CurrentProcess);
322 * The following code is BROKEN.
323 * We are freeing our own stack before entering proc_schedule()
324 * BAJO: A correct fix would be to rearrange the scheduler with
325 * an additional parameter which frees the old stack/process
326 * after a context switch.
328 if (CurrentProcess->flags & PF_FREESTACK)
329 heap_free(CurrentProcess->stack_base, CurrentProcess->stack_size);
330 heap_free(CurrentProcess);
333 #if (ARCH & ARCH_EMUL)
334 #warning This is wrong
335 /* Reinsert process stack in free list */
336 ADDHEAD(&StackFreeList, (Node *)(CurrentProcess->stack
337 - (CONFIG_PROC_DEFSTACKSIZE / sizeof(cpustack_t))));
340 * NOTE: At this point the first two words of what used
341 * to be our stack contain a list node. From now on, we
342 * rely on the compiler not reading/writing the stack.
344 #endif /* ARCH_EMUL */
346 CurrentProcess = NULL;
353 * Co-operative context switch
355 void proc_switch(void)
359 IRQ_SAVE_DISABLE(flags);
360 SCHED_ENQUEUE(CurrentProcess);
368 * Get the pointer to the current process
370 struct Process *proc_current(void)
372 return CurrentProcess;
376 * Get the pointer to the user data of the current process
378 iptr_t proc_current_user_data(void)
380 return CurrentProcess->user_data;
384 #if CONFIG_KERN_PREEMPTIVE
387 * Disable preemptive task switching.
389 * The scheduler maintains a per-process nesting counter. Task switching is
390 * effectively re-enabled only when the number of calls to proc_permit()
391 * matches the number of calls to proc_forbid().
393 * Calling functions that could sleep while task switching is disabled
394 * is dangerous, although supported. Preemptive task switching is
395 * resumed while the process is sleeping and disabled again as soon as
400 void proc_forbid(void)
402 /* No need to protect against interrupts here. */
403 ++CurrentProcess->forbid_cnt;
407 * Re-enable preemptive task switching.
411 void proc_permit(void)
413 /* No need to protect against interrupts here. */
414 --CurrentProcess->forbid_cnt;
417 #endif /* CONFIG_KERN_PREEMPTIVE */