1 /*
2 * FreeRTOS Kernel V11.1.0
3 * Copyright (C) 2021 Amazon.com, Inc. or its affiliates. All Rights Reserved.
4 *
5 * SPDX-License-Identifier: MIT
6 *
7 * Permission is hereby granted, free of charge, to any person obtaining a copy of
8 * this software and associated documentation files (the "Software"), to deal in
9 * the Software without restriction, including without limitation the rights to
10 * use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of
11 * the Software, and to permit persons to whom the Software is furnished to do so,
12 * subject to the following conditions:
13 *
14 * The above copyright notice and this permission notice shall be included in all
15 * copies or substantial portions of the Software.
16 *
17 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
18 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
19 * FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
20 * COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER
21 * IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
22 * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
23 *
24 * https://www.FreeRTOS.org
25 * https://github.com/FreeRTOS
26 *
27 */
28
29 /* Standard includes. */
30 #include <stdlib.h>
31
32 /* Scheduler includes. */
33 #include "FreeRTOS.h"
34 #include "task.h"
35
36 #if configUSE_PORT_OPTIMISED_TASK_SELECTION == 1
37 /* Check the configuration. */
38 #if ( configMAX_PRIORITIES > 32 )
39 #error configUSE_PORT_OPTIMISED_TASK_SELECTION can only be set to 1 when configMAX_PRIORITIES is less than or equal to 32. It is very rare that a system requires more than 10 to 15 difference priorities as tasks that share a priority will time slice.
40 #endif
41 #endif /* configUSE_PORT_OPTIMISED_TASK_SELECTION */
42
43 #ifndef configSETUP_TICK_INTERRUPT
44 #error configSETUP_TICK_INTERRUPT() must be defined in FreeRTOSConfig.h to call the function that sets up the tick interrupt.
45 #endif
46
47 #ifndef configCLEAR_TICK_INTERRUPT
48 #error configCLEAR_TICK_INTERRUPT must be defined in FreeRTOSConfig.h to clear which ever interrupt was used to generate the tick interrupt.
49 #endif
50
51 /* A critical section is exited when the critical section nesting count reaches
52 * this value. */
53 #define portNO_CRITICAL_NESTING ( ( uint32_t ) 0 )
54
55 /* Tasks are not created with a floating point context, but can be given a
56 * floating point context after they have been created. A variable is stored as
57 * part of the tasks context that holds portNO_FLOATING_POINT_CONTEXT if the task
58 * does not have an FPU context, or any other value if the task does have an FPU
59 * context. */
60 #define portNO_FLOATING_POINT_CONTEXT ( ( StackType_t ) 0 )
61
62 /* Constants required to setup the initial task context. */
63 #define portINITIAL_SPSR ( ( StackType_t ) 0x1f ) /* System mode, ARM mode, IRQ enabled FIQ enabled. */
64 #define portTHUMB_MODE_BIT ( ( StackType_t ) 0x20 )
65 #define portTHUMB_MODE_ADDRESS ( 0x01UL )
66
67 /* Masks all bits in the APSR other than the mode bits. */
68 #define portAPSR_MODE_BITS_MASK ( 0x1F )
69
70 /* The value of the mode bits in the APSR when the CPU is executing in user
71 * mode. */
72 #define portAPSR_USER_MODE ( 0x10 )
73
74 /* Let the user override the pre-loading of the initial LR with the address of
75 * prvTaskExitError() in case it messes up unwinding of the stack in the
76 * debugger. */
77 #ifdef configTASK_RETURN_ADDRESS
78 #define portTASK_RETURN_ADDRESS configTASK_RETURN_ADDRESS
79 #else
80 #define portTASK_RETURN_ADDRESS prvTaskExitError
81 #endif
82
83 /*-----------------------------------------------------------*/
84
85 /*
86 * Starts the first task executing. This function is necessarily written in
87 * assembly code so is implemented in portASM.s.
88 */
89 extern void vPortRestoreTaskContext( void );
90
91 /*
92 * Used to catch tasks that attempt to return from their implementing function.
93 */
94 static void prvTaskExitError( void );
95
96 /*-----------------------------------------------------------*/
97
98 /* A variable is used to keep track of the critical section nesting. This
99 * variable has to be stored as part of the task context and must be initialised to
100 * a non zero value to ensure interrupts don't inadvertently become unmasked before
101 * the scheduler starts. As it is stored as part of the task context it will
102 * automatically be set to 0 when the first task is started. */
103 volatile uint32_t ulCriticalNesting = 9999UL;
104
105 /* Saved as part of the task context. If ulPortTaskHasFPUContext is non-zero then
106 * a floating point context must be saved and restored for the task. */
107 volatile uint32_t ulPortTaskHasFPUContext = pdFALSE;
108
109 /* Set to 1 to pend a context switch from an ISR. */
110 volatile uint32_t ulPortYieldRequired = pdFALSE;
111
112 /* Counts the interrupt nesting depth. A context switch is only performed if
113 * if the nesting depth is 0. */
114 volatile uint32_t ulPortInterruptNesting = 0UL;
115
116 /*-----------------------------------------------------------*/
117
118 /*
119 * See header file for description.
120 */
pxPortInitialiseStack(StackType_t * pxTopOfStack,TaskFunction_t pxCode,void * pvParameters)121 StackType_t * pxPortInitialiseStack( StackType_t * pxTopOfStack,
122 TaskFunction_t pxCode,
123 void * pvParameters )
124 {
125 /* Setup the initial stack of the task. The stack is set exactly as
126 * expected by the portRESTORE_CONTEXT() macro.
127 *
128 * The fist real value on the stack is the status register, which is set for
129 * system mode, with interrupts enabled. A few NULLs are added first to ensure
130 * GDB does not try decoding a non-existent return address. */
131 *pxTopOfStack = ( StackType_t ) NULL;
132 pxTopOfStack--;
133 *pxTopOfStack = ( StackType_t ) NULL;
134 pxTopOfStack--;
135 *pxTopOfStack = ( StackType_t ) NULL;
136 pxTopOfStack--;
137 *pxTopOfStack = ( StackType_t ) portINITIAL_SPSR;
138
139 if( ( ( uint32_t ) pxCode & portTHUMB_MODE_ADDRESS ) != 0x00UL )
140 {
141 /* The task will start in THUMB mode. */
142 *pxTopOfStack |= portTHUMB_MODE_BIT;
143 }
144
145 pxTopOfStack--;
146
147 /* Next the return address, which in this case is the start of the task. */
148 *pxTopOfStack = ( StackType_t ) pxCode;
149 pxTopOfStack--;
150
151 /* Next all the registers other than the stack pointer. */
152 *pxTopOfStack = ( StackType_t ) portTASK_RETURN_ADDRESS; /* R14 */
153 pxTopOfStack--;
154 *pxTopOfStack = ( StackType_t ) 0x12121212; /* R12 */
155 pxTopOfStack--;
156 *pxTopOfStack = ( StackType_t ) 0x11111111; /* R11 */
157 pxTopOfStack--;
158 *pxTopOfStack = ( StackType_t ) 0x10101010; /* R10 */
159 pxTopOfStack--;
160 *pxTopOfStack = ( StackType_t ) 0x09090909; /* R9 */
161 pxTopOfStack--;
162 *pxTopOfStack = ( StackType_t ) 0x08080808; /* R8 */
163 pxTopOfStack--;
164 *pxTopOfStack = ( StackType_t ) 0x07070707; /* R7 */
165 pxTopOfStack--;
166 *pxTopOfStack = ( StackType_t ) 0x06060606; /* R6 */
167 pxTopOfStack--;
168 *pxTopOfStack = ( StackType_t ) 0x05050505; /* R5 */
169 pxTopOfStack--;
170 *pxTopOfStack = ( StackType_t ) 0x04040404; /* R4 */
171 pxTopOfStack--;
172 *pxTopOfStack = ( StackType_t ) 0x03030303; /* R3 */
173 pxTopOfStack--;
174 *pxTopOfStack = ( StackType_t ) 0x02020202; /* R2 */
175 pxTopOfStack--;
176 *pxTopOfStack = ( StackType_t ) 0x01010101; /* R1 */
177 pxTopOfStack--;
178 *pxTopOfStack = ( StackType_t ) pvParameters; /* R0 */
179 pxTopOfStack--;
180
181 /* The task will start with a critical nesting count of 0 as interrupts are
182 * enabled. */
183 *pxTopOfStack = portNO_CRITICAL_NESTING;
184 pxTopOfStack--;
185
186 /* The task will start without a floating point context. A task that uses
187 * the floating point hardware must call vPortTaskUsesFPU() before executing
188 * any floating point instructions. */
189 *pxTopOfStack = portNO_FLOATING_POINT_CONTEXT;
190
191 return pxTopOfStack;
192 }
193 /*-----------------------------------------------------------*/
194
prvTaskExitError(void)195 static void prvTaskExitError( void )
196 {
197 /* A function that implements a task must not exit or attempt to return to
198 * its caller as there is nothing to return to. If a task wants to exit it
199 * should instead call vTaskDelete( NULL ).
200 *
201 * Artificially force an assert() to be triggered if configASSERT() is
202 * defined, then stop here so application writers can catch the error. */
203 configASSERT( ulPortInterruptNesting == ~0UL );
204 portDISABLE_INTERRUPTS();
205
206 for( ; ; )
207 {
208 }
209 }
210 /*-----------------------------------------------------------*/
211
xPortStartScheduler(void)212 BaseType_t xPortStartScheduler( void )
213 {
214 uint32_t ulAPSR;
215
216 /* Only continue if the CPU is not in User mode. The CPU must be in a
217 * Privileged mode for the scheduler to start. */
218 __asm volatile ( "MRS %0, APSR" : "=r" ( ulAPSR ) );
219
220 ulAPSR &= portAPSR_MODE_BITS_MASK;
221 configASSERT( ulAPSR != portAPSR_USER_MODE );
222
223 if( ulAPSR != portAPSR_USER_MODE )
224 {
225 /* Start the timer that generates the tick ISR. */
226 portDISABLE_INTERRUPTS();
227 configSETUP_TICK_INTERRUPT();
228
229 /* Start the first task executing. */
230 vPortRestoreTaskContext();
231 }
232
233 /* Will only get here if vTaskStartScheduler() was called with the CPU in
234 * a non-privileged mode or the binary point register was not set to its lowest
235 * possible value. prvTaskExitError() is referenced to prevent a compiler
236 * warning about it being defined but not referenced in the case that the user
237 * defines their own exit address. */
238 ( void ) prvTaskExitError;
239 return 0;
240 }
241 /*-----------------------------------------------------------*/
242
vPortEndScheduler(void)243 void vPortEndScheduler( void )
244 {
245 /* Not implemented in ports where there is nothing to return to.
246 * Artificially force an assert. */
247 configASSERT( ulCriticalNesting == 1000UL );
248 }
249 /*-----------------------------------------------------------*/
250
vPortEnterCritical(void)251 void vPortEnterCritical( void )
252 {
253 portDISABLE_INTERRUPTS();
254
255 /* Now that interrupts are disabled, ulCriticalNesting can be accessed
256 * directly. Increment ulCriticalNesting to keep a count of how many times
257 * portENTER_CRITICAL() has been called. */
258 ulCriticalNesting++;
259
260 /* This is not the interrupt safe version of the enter critical function so
261 * assert() if it is being called from an interrupt context. Only API
262 * functions that end in "FromISR" can be used in an interrupt. Only assert if
263 * the critical nesting count is 1 to protect against recursive calls if the
264 * assert function also uses a critical section. */
265 if( ulCriticalNesting == 1 )
266 {
267 configASSERT( ulPortInterruptNesting == 0 );
268 }
269 }
270 /*-----------------------------------------------------------*/
271
vPortExitCritical(void)272 void vPortExitCritical( void )
273 {
274 if( ulCriticalNesting > portNO_CRITICAL_NESTING )
275 {
276 /* Decrement the nesting count as the critical section is being
277 * exited. */
278 ulCriticalNesting--;
279
280 /* If the nesting level has reached zero then all interrupt
281 * priorities must be re-enabled. */
282 if( ulCriticalNesting == portNO_CRITICAL_NESTING )
283 {
284 /* Critical nesting has reached zero so all interrupt priorities
285 * should be unmasked. */
286 portENABLE_INTERRUPTS();
287 }
288 }
289 }
290 /*-----------------------------------------------------------*/
291
FreeRTOS_Tick_Handler(void)292 void FreeRTOS_Tick_Handler( void )
293 {
294 uint32_t ulInterruptStatus;
295
296 ulInterruptStatus = portSET_INTERRUPT_MASK_FROM_ISR();
297
298 /* Increment the RTOS tick. */
299 if( xTaskIncrementTick() != pdFALSE )
300 {
301 ulPortYieldRequired = pdTRUE;
302 }
303
304 portCLEAR_INTERRUPT_MASK_FROM_ISR( ulInterruptStatus );
305
306 configCLEAR_TICK_INTERRUPT();
307 }
308 /*-----------------------------------------------------------*/
309
vPortTaskUsesFPU(void)310 void vPortTaskUsesFPU( void )
311 {
312 uint32_t ulInitialFPSCR = 0;
313
314 /* A task is registering the fact that it needs an FPU context. Set the
315 * FPU flag (which is saved as part of the task context). */
316 ulPortTaskHasFPUContext = pdTRUE;
317
318 /* Initialise the floating point status register. */
319 __asm volatile ( "FMXR FPSCR, %0" ::"r" ( ulInitialFPSCR ) );
320 }
321 /*-----------------------------------------------------------*/
322
