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RTOSVerySimple/osSimple.c

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+// os.c
+// Runs on LM4F120/TM4C123
+// A very simple real time operating system with minimal features.
+// Jonathan Valvano
+// June 8, 2025
+
+/* 
+ Copyright 2025 by Jonathan W. Valvano, valvano@mail.utexas.edu
+    You may use, edit, run or distribute this file
+    as long as the above copyright notice remains
+ THIS SOFTWARE IS PROVIDED "AS IS".  NO WARRANTIES, WHETHER EXPRESS, IMPLIED
+ OR STATUTORY, INCLUDING, BUT NOT LIMITED TO, IMPLIED WARRANTIES OF
+ MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE APPLY TO THIS SOFTWARE.
+ VALVANO SHALL NOT, IN ANY CIRCUMSTANCES, BE LIABLE FOR SPECIAL, INCIDENTAL,
+ OR CONSEQUENTIAL DAMAGES, FOR ANY REASON WHATSOEVER.
+ For more information about my classes, my research, and my books, see
+ http://users.ece.utexas.edu/~valvano/
+ */
+
+#include <stdint.h>
+#include "osSimple.h"
+
+#include <ti/devices/msp/msp.h>
+#include "../inc/Clock.h"
+
+
+
+
+#define STACKSIZE 100
+uint32_t *tcbs[4];  
+uint32_t RunI;  // index of currently running thread (0,1,2,3)
+uint32_t Stacks[4][STACKSIZE]; 
+void OS_AddThreads(void(*task0)(void), void(*task1)(void),
+                 void(*task2)(void), void(*task3)(void)){ 
+  tcbs[0] = &Stacks[0][STACKSIZE-12]; // thread stack pointer 
+  Stacks[0][STACKSIZE-1] = 0x01000000;   // thumb bit
+  Stacks[0][STACKSIZE-2] = (int32_t)(task0); // PC
+  tcbs[1] = &Stacks[1][STACKSIZE-12]; // thread stack pointer 
+  Stacks[1][STACKSIZE-1] = 0x01000000;   // thumb bit
+  Stacks[1][STACKSIZE-2] = (int32_t)(task1); // PC
+  tcbs[2] = &Stacks[2][STACKSIZE-12]; // thread stack pointer 
+  Stacks[2][STACKSIZE-1] = 0x01000000;   // thumb bit
+  Stacks[2][STACKSIZE-2] = (int32_t)(task2); // PC
+  tcbs[3] = &Stacks[3][STACKSIZE-12]; // thread stack pointer 
+  Stacks[3][STACKSIZE-1] = 0x01000000;   // thumb bit
+  Stacks[3][STACKSIZE-2] = (int32_t)(task3); // PC
+  RunI = 0;       // thread 0 will run first
+}   
+
+
+// ******** OS_Init ************
+// initialize operating system, disable interrupts until OS_Launch
+// input:  none
+// output: none
+void OS_Init(void){
+
+  SysTick->CTRL = 0;         // disable SysTick during setup
+  SysTick->VAL= 0;      // any write to current clears it
+  SCB->SHP[1]    = (SCB->SHP[1]&(~0xC0000000))|(3<<30);  // priority 3
+}
+
+
+
+
+///******** OS_Launch ***************
+// start the scheduler, enable interrupts
+// Inputs: number of 12.5ns clock cycles for each time slice
+//         (maximum of 24 bits)
+// Outputs: none (does not return)
+void OS_Launch(uint32_t theTimeSlice){
+  SysTick->LOAD = theTimeSlice - 1; // reload value
+  SysTick->CTRL = 0x00000007; // enable, core clock and interrupt arm
+  StartOS();                   // start on the first task
+}