1 /*
2 * FreeRTOS Kernel V11.0.1
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 /*
30 * Changes from V2.5.2
31 *
32 + usCriticalNesting now has a volatile qualifier.
33 */
34
35 /* Standard includes. */
36 #include <stdlib.h>
37 #include <signal.h>
38
39 /* Scheduler includes. */
40 #include "FreeRTOS.h"
41 #include "task.h"
42
43 /*-----------------------------------------------------------
44 * Implementation of functions defined in portable.h for the MSP430 port.
45 *----------------------------------------------------------*/
46
47 /* Constants required for hardware setup. The tick ISR runs off the ACLK,
48 * not the MCLK. */
49 #define portACLK_FREQUENCY_HZ ( ( TickType_t ) 32768 )
50 #define portINITIAL_CRITICAL_NESTING ( ( uint16_t ) 10 )
51 #define portFLAGS_INT_ENABLED ( ( StackType_t ) 0x08 )
52
53 /* We require the address of the pxCurrentTCB variable, but don't want to know
54 * any details of its type. */
55 typedef void TCB_t;
56 extern volatile TCB_t * volatile pxCurrentTCB;
57
58 /* Most ports implement critical sections by placing the interrupt flags on
59 * the stack before disabling interrupts. Exiting the critical section is then
60 * simply a case of popping the flags from the stack. As mspgcc does not use
61 * a frame pointer this cannot be done as modifying the stack will clobber all
62 * the stack variables. Instead each task maintains a count of the critical
63 * section nesting depth. Each time a critical section is entered the count is
64 * incremented. Each time a critical section is left the count is decremented -
65 * with interrupts only being re-enabled if the count is zero.
66 *
67 * usCriticalNesting will get set to zero when the scheduler starts, but must
68 * not be initialised to zero as this will cause problems during the startup
69 * sequence. */
70 volatile uint16_t usCriticalNesting = portINITIAL_CRITICAL_NESTING;
71 /*-----------------------------------------------------------*/
72
73 /*
74 * Macro to save a task context to the task stack. This simply pushes all the
75 * general purpose msp430 registers onto the stack, followed by the
76 * usCriticalNesting value used by the task. Finally the resultant stack
77 * pointer value is saved into the task control block so it can be retrieved
78 * the next time the task executes.
79 */
80 #define portSAVE_CONTEXT() \
81 asm volatile ( "push r4 \n\t" \
82 "push r5 \n\t" \
83 "push r6 \n\t" \
84 "push r7 \n\t" \
85 "push r8 \n\t" \
86 "push r9 \n\t" \
87 "push r10 \n\t" \
88 "push r11 \n\t" \
89 "push r12 \n\t" \
90 "push r13 \n\t" \
91 "push r14 \n\t" \
92 "push r15 \n\t" \
93 "mov.w usCriticalNesting, r14 \n\t" \
94 "push r14 \n\t" \
95 "mov.w pxCurrentTCB, r12 \n\t" \
96 "mov.w r1, @r12 \n\t" \
97 );
98
99 /*
100 * Macro to restore a task context from the task stack. This is effectively
101 * the reverse of portSAVE_CONTEXT(). First the stack pointer value is
102 * loaded from the task control block. Next the value for usCriticalNesting
103 * used by the task is retrieved from the stack - followed by the value of all
104 * the general purpose msp430 registers.
105 *
106 * The bic instruction ensures there are no low power bits set in the status
107 * register that is about to be popped from the stack.
108 */
109 #define portRESTORE_CONTEXT() \
110 asm volatile ( "mov.w pxCurrentTCB, r12 \n\t" \
111 "mov.w @r12, r1 \n\t" \
112 "pop r15 \n\t" \
113 "mov.w r15, usCriticalNesting \n\t" \
114 "pop r15 \n\t" \
115 "pop r14 \n\t" \
116 "pop r13 \n\t" \
117 "pop r12 \n\t" \
118 "pop r11 \n\t" \
119 "pop r10 \n\t" \
120 "pop r9 \n\t" \
121 "pop r8 \n\t" \
122 "pop r7 \n\t" \
123 "pop r6 \n\t" \
124 "pop r5 \n\t" \
125 "pop r4 \n\t" \
126 "bic #(0xf0),0(r1) \n\t" \
127 "reti \n\t" \
128 );
129 /*-----------------------------------------------------------*/
130
131 /*
132 * Sets up the periodic ISR used for the RTOS tick. This uses timer 0, but
133 * could have alternatively used the watchdog timer or timer 1.
134 */
135 static void prvSetupTimerInterrupt( void );
136 /*-----------------------------------------------------------*/
137
138 /*
139 * Initialise the stack of a task to look exactly as if a call to
140 * portSAVE_CONTEXT had been called.
141 *
142 * See the header file portable.h.
143 */
pxPortInitialiseStack(StackType_t * pxTopOfStack,TaskFunction_t pxCode,void * pvParameters)144 StackType_t * pxPortInitialiseStack( StackType_t * pxTopOfStack,
145 TaskFunction_t pxCode,
146 void * pvParameters )
147 {
148 /*
149 * Place a few bytes of known values on the bottom of the stack.
150 * This is just useful for debugging and can be included if required.
151 *
152 * pxTopOfStack = ( StackType_t ) 0x1111;
153 * pxTopOfStack--;
154 * pxTopOfStack = ( StackType_t ) 0x2222;
155 * pxTopOfStack--;
156 * pxTopOfStack = ( StackType_t ) 0x3333;
157 * pxTopOfStack--;
158 */
159
160 /* The msp430 automatically pushes the PC then SR onto the stack before
161 * executing an ISR. We want the stack to look just as if this has happened
162 * so place a pointer to the start of the task on the stack first - followed
163 * by the flags we want the task to use when it starts up. */
164 *pxTopOfStack = ( StackType_t ) pxCode;
165 pxTopOfStack--;
166 *pxTopOfStack = portFLAGS_INT_ENABLED;
167 pxTopOfStack--;
168
169 /* Next the general purpose registers. */
170 *pxTopOfStack = ( StackType_t ) 0x4444;
171 pxTopOfStack--;
172 *pxTopOfStack = ( StackType_t ) 0x5555;
173 pxTopOfStack--;
174 *pxTopOfStack = ( StackType_t ) 0x6666;
175 pxTopOfStack--;
176 *pxTopOfStack = ( StackType_t ) 0x7777;
177 pxTopOfStack--;
178 *pxTopOfStack = ( StackType_t ) 0x8888;
179 pxTopOfStack--;
180 *pxTopOfStack = ( StackType_t ) 0x9999;
181 pxTopOfStack--;
182 *pxTopOfStack = ( StackType_t ) 0xaaaa;
183 pxTopOfStack--;
184 *pxTopOfStack = ( StackType_t ) 0xbbbb;
185 pxTopOfStack--;
186 *pxTopOfStack = ( StackType_t ) 0xcccc;
187 pxTopOfStack--;
188 *pxTopOfStack = ( StackType_t ) 0xdddd;
189 pxTopOfStack--;
190 *pxTopOfStack = ( StackType_t ) 0xeeee;
191 pxTopOfStack--;
192
193 /* When the task starts is will expect to find the function parameter in
194 * R15. */
195 *pxTopOfStack = ( StackType_t ) pvParameters;
196 pxTopOfStack--;
197
198 /* The code generated by the mspgcc compiler does not maintain separate
199 * stack and frame pointers. The portENTER_CRITICAL macro cannot therefore
200 * use the stack as per other ports. Instead a variable is used to keep
201 * track of the critical section nesting. This variable has to be stored
202 * as part of the task context and is initially set to zero. */
203 *pxTopOfStack = ( StackType_t ) portNO_CRITICAL_SECTION_NESTING;
204
205 /* Return a pointer to the top of the stack we have generated so this can
206 * be stored in the task control block for the task. */
207 return pxTopOfStack;
208 }
209 /*-----------------------------------------------------------*/
210
xPortStartScheduler(void)211 BaseType_t xPortStartScheduler( void )
212 {
213 /* Setup the hardware to generate the tick. Interrupts are disabled when
214 * this function is called. */
215 prvSetupTimerInterrupt();
216
217 /* Restore the context of the first task that is going to run. */
218 portRESTORE_CONTEXT();
219
220 /* Should not get here as the tasks are now running! */
221 return pdTRUE;
222 }
223 /*-----------------------------------------------------------*/
224
vPortEndScheduler(void)225 void vPortEndScheduler( void )
226 {
227 /* It is unlikely that the MSP430 port will get stopped. If required simply
228 * disable the tick interrupt here. */
229 }
230 /*-----------------------------------------------------------*/
231
232 /*
233 * Manual context switch called by portYIELD or taskYIELD.
234 *
235 * The first thing we do is save the registers so we can use a naked attribute.
236 */
237 void vPortYield( void ) __attribute__( ( naked ) );
vPortYield(void)238 void vPortYield( void )
239 {
240 /* We want the stack of the task being saved to look exactly as if the task
241 * was saved during a pre-emptive RTOS tick ISR. Before calling an ISR the
242 * msp430 places the status register onto the stack. As this is a function
243 * call and not an ISR we have to do this manually. */
244 asm volatile ( "push r2" );
245 _DINT();
246
247 /* Save the context of the current task. */
248 portSAVE_CONTEXT();
249
250 /* Switch to the highest priority task that is ready to run. */
251 vTaskSwitchContext();
252
253 /* Restore the context of the new task. */
254 portRESTORE_CONTEXT();
255 }
256 /*-----------------------------------------------------------*/
257
258 /*
259 * Hardware initialisation to generate the RTOS tick. This uses timer 0
260 * but could alternatively use the watchdog timer or timer 1.
261 */
prvSetupTimerInterrupt(void)262 static void prvSetupTimerInterrupt( void )
263 {
264 /* Ensure the timer is stopped. */
265 TACTL = 0;
266
267 /* Run the timer of the ACLK. */
268 TACTL = TASSEL_1;
269
270 /* Clear everything to start with. */
271 TACTL |= TACLR;
272
273 /* Set the compare match value according to the tick rate we want. */
274 TACCR0 = portACLK_FREQUENCY_HZ / configTICK_RATE_HZ;
275
276 /* Enable the interrupts. */
277 TACCTL0 = CCIE;
278
279 /* Start up clean. */
280 TACTL |= TACLR;
281
282 /* Up mode. */
283 TACTL |= MC_1;
284 }
285 /*-----------------------------------------------------------*/
286
287 /*
288 * The interrupt service routine used depends on whether the pre-emptive
289 * scheduler is being used or not.
290 */
291
292 #if configUSE_PREEMPTION == 1
293
294 /*
295 * Tick ISR for preemptive scheduler. We can use a naked attribute as
296 * the context is saved at the start of vPortYieldFromTick(). The tick
297 * count is incremented after the context is saved.
298 */
299 interrupt( TIMERA0_VECTOR ) prvTickISR( void ) __attribute__( ( naked ) );
prvTickISR(void)300 interrupt( TIMERA0_VECTOR ) prvTickISR( void )
301 {
302 /* Save the context of the interrupted task. */
303 portSAVE_CONTEXT();
304
305 /* Increment the tick count then switch to the highest priority task
306 * that is ready to run. */
307 if( xTaskIncrementTick() != pdFALSE )
308 {
309 vTaskSwitchContext();
310 }
311
312 /* Restore the context of the new task. */
313 portRESTORE_CONTEXT();
314 }
315
316 #else /* if configUSE_PREEMPTION == 1 */
317
318 /*
319 * Tick ISR for the cooperative scheduler. All this does is increment the
320 * tick count. We don't need to switch context, this can only be done by
321 * manual calls to taskYIELD();
322 */
323 interrupt( TIMERA0_VECTOR ) prvTickISR( void );
prvTickISR(void)324 interrupt( TIMERA0_VECTOR ) prvTickISR( void )
325 {
326 xTaskIncrementTick();
327 }
328 #endif /* if configUSE_PREEMPTION == 1 */
329
