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193 lines
6.8 KiB
C
193 lines
6.8 KiB
C
1 year ago
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/****************************************************************************
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* MInimal Real-time Operating System (MiROS), ARM-CLANG port.
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* version 0.24 (matching lesson 24)
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*
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* This software is a teaching aid to illustrate the concepts underlying
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* a Real-Time Operating System (RTOS). The main goal of the software is
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* simplicity and clear presentation of the concepts, but without dealing
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* with various corner cases, portability, or error handling. For these
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* reasons, the software is generally NOT intended or recommended for use
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* in commercial applications.
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*
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* Copyright (C) 2018 Miro Samek. All Rights Reserved.
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*
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* SPDX-License-Identifier: GPL-3.0-or-later
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*
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* This program is free software: you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation, either version 3 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program. If not, see <https://www.gnu.org/licenses/>.
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*
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* Git repo:
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* https://github.com/QuantumLeaps/MiROS
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****************************************************************************/
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#include <stdint.h>
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#include "miros.h"
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#include "qassert.h"
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Q_DEFINE_THIS_FILE
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OSThread * volatile OS_curr; /* pointer to the current thread */
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OSThread * volatile OS_next; /* pointer to the next thread to run */
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OSThread *OS_thread[32 + 1]; /* array of threads started so far */
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uint8_t OS_threadNum; /* number of threads started so far */
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uint8_t OS_currIdx; /* current thread index for round robin scheduling */
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void OS_init(void) {
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/* set the PendSV interrupt priority to the lowest level 0xFF */
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*(uint32_t volatile *)0xE000ED20 |= (0xFFU << 16);
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}
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void OS_sched(void) {
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/* OS_next = ... */
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++OS_currIdx;
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if (OS_currIdx == OS_threadNum) {
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OS_currIdx = 0U;
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}
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OS_next = OS_thread[OS_currIdx];
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/* trigger PendSV, if needed */
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if (OS_next != OS_curr) {
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*(uint32_t volatile *)0xE000ED04 = (1U << 28);
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}
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}
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void OS_run(void) {
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/* callback to configure and start interrupts */
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OS_onStartup();
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__asm volatile ("cpsid i");
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OS_sched();
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__asm volatile ("cpsie i");
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/* the following code should never execute */
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Q_ERROR();
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}
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void OSThread_start(
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OSThread *me,
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OSThreadHandler threadHandler,
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void *stkSto, uint32_t stkSize)
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{
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/* round down the stack top to the 8-byte boundary
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* NOTE: ARM Cortex-M stack grows down from hi -> low memory
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*/
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uint32_t *sp = (uint32_t *)((((uint32_t)stkSto + stkSize) / 8) * 8);
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uint32_t *stk_limit;
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*(--sp) = (1U << 24); /* xPSR */
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*(--sp) = (uint32_t)threadHandler; /* PC */
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*(--sp) = 0x0000000EU; /* LR */
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*(--sp) = 0x0000000CU; /* R12 */
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*(--sp) = 0x00000003U; /* R3 */
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*(--sp) = 0x00000002U; /* R2 */
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*(--sp) = 0x00000001U; /* R1 */
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*(--sp) = 0x00000000U; /* R0 */
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/* additionally, fake registers R4-R11 */
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*(--sp) = 0x0000000BU; /* R11 */
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*(--sp) = 0x0000000AU; /* R10 */
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*(--sp) = 0x00000009U; /* R9 */
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*(--sp) = 0x00000008U; /* R8 */
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*(--sp) = 0x00000007U; /* R7 */
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*(--sp) = 0x00000006U; /* R6 */
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*(--sp) = 0x00000005U; /* R5 */
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*(--sp) = 0x00000004U; /* R4 */
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/* save the top of the stack in the thread's attibute */
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me->sp = sp;
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/* round up the bottom of the stack to the 8-byte boundary */
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stk_limit = (uint32_t *)(((((uint32_t)stkSto - 1U) / 8) + 1U) * 8);
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/* pre-fill the unused part of the stack with 0xDEADBEEF */
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for (sp = sp - 1U; sp >= stk_limit; --sp) {
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*sp = 0xDEADBEEFU;
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}
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Q_ASSERT(OS_threadNum < Q_DIM(OS_thread));
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/* register the thread with the OS */
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OS_thread[OS_threadNum] = me;
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++OS_threadNum;
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}
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/* inline assembly syntax for Compiler 6 (ARMCLANG) */
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__attribute__ ((naked))
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void PendSV_Handler(void) {
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__asm volatile (
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/* __disable_irq(); */
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" CPSID I \n"
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/* if (OS_curr != (OSThread *)0) { */
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" LDR r1,=OS_curr \n"
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" LDR r1,[r1,#0x00] \n"
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" CMP r1,#0 \n"
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" BEQ PendSV_restore \n"
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/* push registers r4-r11 on the stack */
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#if (__ARM_ARCH == 6) // if ARMv6-M...
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" SUB sp,sp,#(8*4) \n" // make room for 8 registers r4-r11
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" MOV r0,sp \n" // r0 := temporary stack pointer
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" STMIA r0!,{r4-r7} \n" // save the low registers
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" MOV r4,r8 \n" // move the high registers to low registers...
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" MOV r5,r9 \n"
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" MOV r6,r10 \n"
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" MOV r7,r11 \n"
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" STMIA r0!,{r4-r7} \n" // save the high registers
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#else // ARMv7-M or higher
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" PUSH {r4-r11} \n"
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#endif // ARMv7-M or higher
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/* OS_curr->sp = sp; */
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" LDR r1,=OS_curr \n"
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" LDR r1,[r1,#0x00] \n"
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" MOV r0,sp \n"
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" STR r0,[r1,#0x00] \n"
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/* } */
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"PendSV_restore: \n"
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/* sp = OS_next->sp; */
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" LDR r1,=OS_next \n"
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" LDR r1,[r1,#0x00] \n"
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" LDR r0,[r1,#0x00] \n"
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" MOV sp,r0 \n"
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/* OS_curr = OS_next; */
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" LDR r1,=OS_next \n"
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" LDR r1,[r1,#0x00] \n"
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" LDR r2,=OS_curr \n"
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" STR r1,[r2,#0x00] \n"
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/* pop registers r4-r11 */
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#if (__ARM_ARCH == 6) // if ARMv6-M...
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" MOV r0,sp \n" // r0 := top of stack
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" MOV r2,r0 \n"
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" ADDS r2,r2,#(4*4) \n" // point r2 to the 4 high registers r7-r11
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" LDMIA r2!,{r4-r7} \n" // pop the 4 high registers into low registers
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" MOV r8,r4 \n" // move low registers into high registers
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" MOV r9,r5 \n"
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" MOV r10,r6 \n"
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" MOV r11,r7 \n"
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" LDMIA r0!,{r4-r7} \n" // pop the low registers
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" ADD sp,sp,#(8*4) \n" // remove 8 registers from the stack
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#else // ARMv7-M or higher
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" POP {r4-r11} \n"
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#endif // ARMv7-M or higher
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/* __enable_irq(); */
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" CPSIE I \n"
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/* return to the next thread */
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" BX lr \n"
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);
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}
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