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 2010 Develer S.r.l. (http://www.develer.com/)
33 * \brief Cortex-M3 architecture's entry point
35 * \author Andrea Righi <arighi@develer.com>
38 #include <cfg/compiler.h>
39 #include <cfg/cfg_proc.h> /* CONFIG_KERN_PREEMPT */
40 #include <kern/proc_p.h>
41 #include <cfg/debug.h>
42 #include <cpu/attr.h> /* PAUSE */
43 #include <cpu/irq.h> /* IRQ_DISABLE */
44 #include <cpu/types.h>
45 #include "drv/irq_lm3s.h"
46 #include "drv/clock_lm3s.h"
49 extern size_t __text_end, __data_start, __data_end, __bss_start, __bss_end;
51 extern void __init2(void);
53 #if CONFIG_KERN_PREEMPT
55 * Kernel preemption: implementation details.
57 * The kernel preemption is implemented using the PendSV IRQ. Inside the
58 * SysTick handler when a process needs to be interrupted (expires its time
59 * quantum or a high-priority process is awakend) a pending PendSV call is
62 * The PendSV handler is called immediately after the SysTick handler, using
63 * the architecture's tail-chaining functionality (an ISR call without the
64 * overhead of state saving and restoration between different IRQs). Inside the
65 * PendSV handler we perform the stack-switching between the old and new
68 * Voluntary context switch is implemented as a soft-interrupt call (SVCall),
69 * so any process is always suspended and resumed from an interrupt context.
71 * NOTE: interrupts must be disabled or enabled when resuming a process context
72 * depending of the type of the previous suspension. If a process was suspended
73 * by a voluntary context switch IRQs must be disabled on resume (voluntary
74 * context switch always happen with IRQs disabled). Instead, if a process was
75 * suspended by the kernel preemption IRQs must be always re-enabled, because
76 * the PendSV handler resumes directly the process context. To keep track of
77 * this, we save the state of the IRQ priority in register r3 before performing
80 * If CONFIG_KERN_PREEMPT is not enabled the cooperative implementation
81 * fallbacks to the default stack-switching mechanism, performed directly in
82 * thread-mode and implemented as a normal function call.
86 * Voluntary context switch handler.
88 static void NAKED svcall_handler(void)
94 "stmdb ip!, {r3-r11, lr}\n\t"
99 "ldmia ip!, {r3-r11, lr}\n\t"
101 "msr basepri, r3\n\t"
102 "bx lr" : : : "memory");
106 * Preemptible context switch handler.
108 static void NAKED pendsv_handler(void)
110 register cpu_stack_t *stack asm("ip");
113 "mrs r3, basepri\n\t"
115 "msr basepri, %0\n\t"
117 "stmdb %0!, {r3-r11, lr}\n\t"
119 : "r"(stack), "i"(IRQ_PRIO_DISABLED)
121 proc_current()->stack = stack;
123 stack = proc_current()->stack;
125 "ldmia %0!, {r3-r11, lr}\n\t"
127 "msr basepri, r3\n\t"
129 : "=r"(stack) : "r"(stack)
134 /* Architecture's entry point */
138 * The main application expects IRQs disabled.
143 * PLL may not function properly at default LDO setting.
147 * In designs that enable and use the PLL module, unstable device
148 * behavior may occur with the LDO set at its default of 2.5 volts or
149 * below (minimum of 2.25 volts). Designs that do not use the PLL
150 * module are not affected.
152 * Workaround: Prior to enabling the PLL module, it is recommended that
153 * the default LDO voltage setting of 2.5 V be adjusted to 2.75 V using
154 * the LDO Power Control (LDOPCTL) register.
156 * Silicon Revision Affected: A1, A2
158 * See also: Stellaris LM3S1968 A2 Errata documentation.
160 if (REVISION_IS_A1 | REVISION_IS_A2)
161 HWREG(SYSCTL_LDOPCTL) = SYSCTL_LDOPCTL_2_75V;
163 /* Set the appropriate clocking configuration */
166 /* Initialize IRQ vector table in RAM */
169 #if CONFIG_KERN_PREEMPT
171 * Voluntary context switch handler.
173 * This software interrupt can always be triggered and must be
174 * dispatched as soon as possible, thus we just disable IRQ priority
177 sysirq_setHandler(FAULT_SVCALL, svcall_handler);
178 sysirq_setPriority(FAULT_SVCALL, IRQ_PRIO_MAX);
180 * Preemptible context switch handler
182 * The priority of this IRQ must be the lowest priority in the system
183 * in order to run last in the interrupt service routines' chain.
185 sysirq_setHandler(FAULT_PENDSV, pendsv_handler);
186 sysirq_setPriority(FAULT_PENDSV, IRQ_PRIO_MIN);