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 2008 Bernie Innocenti <bernie@codewiz.org>
32 * \brief Simple preemptive multitasking scheduler.
34 * \version $Id: proc.c 1616 2008-08-10 19:41:26Z bernie $
35 * \author Bernie Innocenti <bernie@codewiz.org>
42 #include <kern/monitor.h>
43 #include <cpu/frame.h> // CPU_IDLE
44 #include <drv/timer.h>
45 #include <cfg/module.h>
52 * Disable preemptive task switching.
54 * The scheduler maintains a per-process nesting counter. Task switching is
55 * effectively re-enabled only when the number of calls to proc_permit()
56 * matches the number of calls to proc_forbid().
58 * Calling functions that could sleep while task switching is disabled
59 * is dangerous, although supported. Preemptive task switching is
60 * resumed while the process is sleeping and disabled again as soon as
65 void proc_forbid(void)
67 /* No need to protect against interrupts here. */
68 ++CurrentProcess->forbid_cnt;
72 * Re-enable preemptive task switching.
76 void proc_permit(void)
78 /* No need to protect against interrupts here. */
79 --CurrentProcess->forbid_cnt;
83 void proc_preempt(void)
87 LIST_ASSERT_VALID(&ProcReadyList);
88 CurrentProcess = (struct Process *)list_remHead(&ProcReadyList);
89 LIST_ASSERT_VALID(&ProcReadyList);
90 ASSERT2(CurrentProcess, "no idle proc?");
94 TRACEMSG("new proc: %p:%s", CurrentProcess, CurrentProcess ? CurrentProcess->monitor.name : "---");
98 void proc_preempt_timer(UNUSED_ARG(void *, param))
102 if (!CurrentProcess->forbid_cnt)
104 TRACEMSG("preempting %p:%s", CurrentProcess, CurrentProcess->monitor.name);
105 LIST_ASSERT_VALID(&ProcReadyList);
106 SCHED_ENQUEUE(CurrentProcess);
112 timer_setDelay(&preempt_timer, CONFIG_KERN_QUANTUM);
113 timer_add(&preempt_timer);
116 void proc_schedule(void)
120 // Will invoke proc_preempt() in interrupt context
124 void proc_yield(void)
128 ASSERT_IRQ_ENABLED();
130 SCHED_ENQUEUE(CurrentProcess);
131 LIST_ASSERT_VALID(&ProcReadyList);
136 void proc_entry(void (*user_entry)(void))
143 static cpustack_t idle_stack[CONFIG_PROC_DEFSTACKSIZE / sizeof(cpustack_t)];
148 * This process never dies and never sleeps. It's also quite apathic
149 * and a bit antisocial.
151 * Having an idle process costs some stack space, but simplifies the
152 * interrupt-driven preemption logic because there is always a user
153 * context to which we can return.
155 static NORETURN void idle(void)
161 proc_yield(); // FIXME: CPU_IDLE
165 void preempt_init(void)
170 irq_register(SIGUSR1, proc_preempt);
172 timer_setSoftint(&preempt_timer, proc_preempt_timer, NULL);
173 timer_setDelay(&preempt_timer, CONFIG_KERN_QUANTUM);
174 timer_add(&preempt_timer);
176 proc_new(idle, NULL, sizeof(idle_stack), idle_stack);