Added a basic SysTick Scheduler

coder137 · coder137 · commit 3069fe61f0bc · 2021-01-02T22:33:58.000-08:00
- Does not contain priorities
- Can only add 3 threads
diff --git a/Systick_Scheduler/.vscode/launch.json b/Systick_Scheduler/.vscode/launch.json
@@ -2,7 +2,7 @@
   "configurations": [
     {
       "cwd": "${workspaceFolder}",
-      "executable": "build/SVC_Handler.elf",
+      "executable": "build/Systick_Scheduler.elf",
       "configFiles": [
         "stm32l4discovery.cfg"
       ],
@@ -16,7 +16,7 @@
     },
     {
       "cwd": "${workspaceFolder}",
-      "executable": "build/SVC_Handler.elf",
+      "executable": "build/Systick_Scheduler.elf",
       "configFiles": [
         "stm32l4discovery.cfg"
       ],
diff --git a/Systick_Scheduler/CMakeLists.txt b/Systick_Scheduler/CMakeLists.txt
@@ -6,7 +6,9 @@ set(CONTROLLER_NAME "STM32L475xx")
 
 # Project start
 set(CMAKE_TOOLCHAIN_FILE "cmake/toolchain.cmake")
-project(${PROJECT_NAME})
+project(${PROJECT_NAME}
+  LANGUAGES C ASM
+)
 
 # Get compiler and linker flags from here
 include(cmake/flags.cmake)
@@ -29,6 +31,7 @@ target_link_options(${USER_PROJECT_TARGET} PRIVATE
 # TODO, Add more subdirectories here
 add_subdirectory(l0_lowlevel)
 add_subdirectory(modules)
+add_subdirectory(application)
 
 # Tools and various custom targets
 include(cmake/targets.cmake)
diff --git a/Systick_Scheduler/README.md b/Systick_Scheduler/README.md
@@ -0,0 +1,61 @@
+# SysTick Scheduler
+
+- Does not contain priorities
+- Currently cannot dynamically add threads
+
+## Pre-Requisites
+
+- Linked List for stack and thread functions
+```c
+struct tcb {
+  uint32_t *stackPt;
+  struct tcb *nextPt;
+};
+typedef struct tcb tcbType;
+```
+- Scheduler Launch
+- Systick Handler for loading threads and timekeeping
+
+# Steps
+
+## Adding Threads
+
+- Each `tcb.nextPt` should point to the next `tcb`
+  - The last `tcb` should point to the first `tcb` as a linked list
+- The `tcb.stackPt` should point to the first free stack space that can be used
+  - `[STACKSIZE - 16]`
+  - In ascending to descending order (99-84)
+  - xPSR
+  - PC
+  - LR
+  - r12
+  - r3
+  - r2
+  - r1
+  - r0
+  - r11
+  - r10
+  - r9
+  - r8
+  - r7
+  - r6
+  - r5
+  - r4
+- Make sure `xPSR` register is in thumb state i.e `[STACKSIZE - 1] = 0x01000000;`
+- Make sure `PC` register points to the thread function
+
+## Launching Threads
+
+- Make sure your SysTick is configured appropriately (with an appropriate quanta size)
+- Load the `SP` to `currentPt->stackPt`
+- POP all values from `R4-R11`, `R0-R3`, `R12`
+- POP `LR`
+
+## SysTick Handler
+
+- PUSH `R4-R11` on the stack
+  - Including the above registers
+- Store old `SP` to `currentPt->stackPt`
+- Move to the next linked list
+  - `current = current->nextPt`
+  - Load new `SP` to `currentPt->stackPt`
diff --git a/Systick_Scheduler/application/CMakeLists.txt b/Systick_Scheduler/application/CMakeLists.txt
@@ -0,0 +1,7 @@
+target_sources(${USER_PROJECT_TARGET} PRIVATE
+  osKernel.c
+  osKernel.S
+)
+target_include_directories(${USER_PROJECT_TARGET} PRIVATE
+  .
+)
diff --git a/Systick_Scheduler/application/main.c b/Systick_Scheduler/application/main.c
@@ -1,112 +1,31 @@
-#include <stdint.h>
-#include <stdlib.h>
-#include <string.h>
+#include "osKernel.h"
 
-#include "gpio/gpio.h"
-#include "uart/uart.h"
+// * Add these variables to the debug watch window
+static uint32_t i, j, k;
 
-// NOTE, code cannot be a variable it has to be an immediate value (constant
-// value)
-#define SVC(code) __ASM volatile("svc %0" : : "I"(code) : "memory")
-
-// Static functions
-
-// SVC Services
-static uint32_t svc_service_add(uint32_t a, uint32_t b);
-// TODO, Define more svc services here
-
-// UART
-static void main__uart_init(void);
-
-// State Variables
-static UART_s uart_config;
-
-// Stack contains:
-// (When there is NO floating point)
-// Page 40 of `Cortex M4 Generic User guide`
-// r0, r1, r2, r3, r12, LR, PC and xPSR (from svc_args[0] - svc_args[7])
-// First argument (r0) is svc_args[0]
-// PC - 2
-void SVC_Handler_Main(unsigned int *svc_args) {
-  // char *r0_address = (char *)svc_args[0];
-  // char *lr_address = (char *)svc_args[5];
-  // char *pc_address = (char *)svc_args[6];
+void t1(void) {
+  while (1) {
+    i++;
+  }
+}
 
-  uint32_t svc_number = ((char *)svc_args[6])[-2];
-  switch (svc_number) {
-  // Add operation
-  case 3:
-    svc_args[2] = svc_args[0] + svc_args[1];
-    break;
-  default:
-    break;
+void t2(void) {
+  while (1) {
+    j++;
   }
 }
 
-// * This attribute is VERY IMPORTANT
-// Compile with O0 to see the difference with and without
-// the __attribute__((naked)) option
-__attribute__((naked)) void SVC_Handler(void) {
-  __ASM volatile(".global SVC_Handler_Main\n"
-                 "TST lr, #4\n"
-                 "ITE EQ\n"
-                 "MRSEQ r0, MSP\n"
-                 "MRSNE r0, PSP\n"
-                 "B SVC_Handler_Main\n" ::
-                     : "memory");
+void t3(void) {
+  while (1) {
+    k++;
+  }
 }
 
 int main(void) {
-  main__uart_init();
-  uart__write_string(&uart_config, "Hello World\r\n");
-  char buffer[20] = {0};
-
-  uint32_t value, new_value;
-  value = svc_service_add(3, 4);
-  __itoa(value, buffer, 10);
-  uart__write_string(&uart_config, buffer);
-  memset(buffer, 0, sizeof(buffer));
-
-  new_value = svc_service_add(2, 3);
-  __itoa(new_value, buffer, 10);
-  uart__write_string(&uart_config, buffer);
-  memset(buffer, 0, sizeof(buffer));
-
-  (void)value;
-  (void)new_value;
-
+  osKernelAddThreads(t1, t2, t3);
+  osKernelLaunch(10);
   while (1) {
   }
 
   return 0;
 }
-
-// STATIC FUNCTION
-static void main__uart_init(void) {
-  // Activate USART1
-  RCC->APB2ENR |= (1 << 14);
-  // Activate GPIOB
-  RCC->AHB2ENR |= (1 << 1);
-
-  GPIO_s config = {};
-  config.mode = GPIO_mode_ALTERNATE_FUNCTION;
-  config.type = GPIO_type_PUSH_PULL;
-  config.speed = GPIO_speed_VERY_HIGH_SPEED;
-  config.pull = GPIO_pull_NO_PULLUP_OR_PULLDOWN;
-  config.alternate = GPIO_alternate_7;
-  gpio__init(&config, GPIOB, 6);
-  gpio__init(&config, GPIOB, 7);
-
-  uart_config.baud_rate = 115200U;
-  uart_config.stop_bit = UART_stop_bit_1_0;
-  uart_config.word_length = UART_word_length_8;
-  uart_config.mode = UART_mode_RX_TX;
-  uart__init(&uart_config, USART1);
-}
-
-uint32_t svc_service_add(uint32_t a, uint32_t b) {
-  SVC(3);
-  // Named Register Variables
-  register uint32_t r2_data __ASM("r2");
-  return r2_data;
-}
diff --git a/Systick_Scheduler/application/osKernel.S b/Systick_Scheduler/application/osKernel.S
@@ -0,0 +1,36 @@
+  .global currentPt
+
+  .text 32
+  .align 4
+  .syntax unified
+
+  .global SysTick_Handler
+  .thumb_func
+SysTick_Handler:
+  CPSID i
+  PUSH {R4-R11}
+  LDR R0,=currentPt     @ R0 points to currentPt
+  LDR R1,[R0]           @ Load currentPt to R1
+  STR SP,[R1]           @ Store SP to address at current->stackPt
+  LDR R1, [R1, #4]      @ r1 = currentPt->next
+  STR R1, [R0]          @ currentPt = r1
+  LDR SP, [R1]          @ SP = currentPt->stackPt
+  POP {R4-R11}
+  CPSIE i
+  BX LR
+
+
+  .global osSchedulerLaunch
+  .thumb_func
+osSchedulerLaunch:
+  LDR R0,=currentPt
+  LDR R2,[R0]       @ R2 = currentPt
+  LDR SP,[R2]       @ SP = currentPt->stackPt
+  POP {R4-R11}
+  POP {R0-R3}
+  POP {R12}
+  ADD SP,SP,#4
+  POP {LR}
+  ADD SP,SP,#4
+  CPSIE i
+  BX LR
diff --git a/Systick_Scheduler/application/osKernel.c b/Systick_Scheduler/application/osKernel.c
@@ -0,0 +1,82 @@
+#include "osKernel.h"
+
+#include "stm32l4xx.h"
+
+// Constants
+#define NUM_OF_THREADS 3
+#define STACKSIZE 100
+struct tcb {
+  uint32_t *stackPt;
+  struct tcb *nextPt;
+};
+typedef struct tcb tcbType;
+
+// Static functions
+static void osKernelStackInit(int thread_number);
+
+// Calls the assembly function
+extern void osSchedulerLaunch(void);
+
+// State variables
+static tcbType tcbs[NUM_OF_THREADS];
+static uint32_t TCB_STACK[NUM_OF_THREADS][STACKSIZE];
+
+// * NOTE, Do not make this static since it is used by the osKernel.S file
+tcbType *currentPt;
+
+uint8_t osKernelAddThreads(void (*thread0)(void), void (*thread1)(void),
+                           void (*thread2)(void)) {
+  __disable_irq();
+
+  // Create a Circular Linked list here
+  tcbs[0].nextPt = &tcbs[1];
+  tcbs[1].nextPt = &tcbs[2];
+  tcbs[2].nextPt = &tcbs[0];
+
+  osKernelStackInit(0);
+  TCB_STACK[0][STACKSIZE - 2] = (uint32_t)thread0;
+
+  osKernelStackInit(1);
+  TCB_STACK[1][STACKSIZE - 2] = (uint32_t)thread1;
+
+  osKernelStackInit(2);
+  TCB_STACK[2][STACKSIZE - 2] = (uint32_t)thread2;
+
+  // Initialize the currentPt
+  currentPt = &tcbs[0];
+  __enable_irq();
+  return 1;
+}
+
+void osKernelLaunch(uint32_t quanta) {
+  // Disable the SysTick
+  SysTick->CTRL = 0;
+
+  // Reset the initial value
+  SysTick->VAL = 0;
+
+  // Set the lowest priority (largest possible value)
+  NVIC_SetPriority(SysTick_IRQn, (1 << __NVIC_PRIO_BITS) - 1);
+
+  // Set the counter
+  const uint32_t MILLIS_PRESCALER = SystemCoreClock / 1000;
+  SysTick->LOAD = quanta * MILLIS_PRESCALER - 1;
+
+  // Enable the SysTick source
+  // enable = 1, tickint = 1, CLKSOURCE=Processor Clock (SystemCoreClock)
+  SysTick->CTRL = 0x07;
+  osSchedulerLaunch();
+}
+
+// Static functions
+static void osKernelStackInit(int thread_number) {
+  // STACKSIZE = 100
+  // Last value is 99
+  // 100 - 16 => 84 uint32_t value to be stored
+  tcbs[thread_number].stackPt = &TCB_STACK[thread_number][STACKSIZE - 16];
+
+  // xPSR value needs to be in the thumb state
+  // xPSR, PC, LR, r12, r3, r2, r1, r0
+  // r11, r10, r9, r8, r7, r6, r5, r4
+  TCB_STACK[thread_number][STACKSIZE - 1] = 0x01000000;
+}
diff --git a/Systick_Scheduler/application/osKernel.h b/Systick_Scheduler/application/osKernel.h
@@ -0,0 +1,11 @@
+#ifndef OS_KERNEL_H_
+#define OS_KERNEL_H_
+
+#include <stdint.h>
+
+uint8_t osKernelAddThreads(void (*thread0)(void), void (*thread1)(void),
+                           void (*thread2)(void));
+
+void osKernelLaunch(uint32_t quanta);
+
+#endif
