Add ARM spinlock

Makefile

@@ -1,19 +1,22 @@
-CC = arm-none-eabi-gcc
-AS = arm-none-eabi-as
-LD = arm-none-eabi-ld
+TOOLCHAIN = arm-none-eabi
+
+CC = $(TOOLCHAIN)-gcc
+AS = $(TOOLCHAIN)-as
+LD = $(TOOLCHAIN)-ld
 CPU = -mcpu=cortex-m4
 THUMB = -mthumb
 
 LDFLAGS = -T linker.ld
 CFLAGS = $(CPU) $(THUMB) -I libc/ -I ./
+CC_SYMBOLS = -DTOOLCHAIN_GCC_ARM
 
 QEMU = qemu-system-arm
-BOARD = netduino2
+BOARD = netduinoplus2
 
 # Output file
 TARGET = main.elf
 # Source files
-SRCS = os/main.c os/process.c os/scheduler.c os/alloc.c os/delay.c os/driver/usart.c libc/library.c tasks/tasks.c
+SRCS = os/main.c os/process.c os/scheduler.c os/alloc.c os/delay.c os/driver/usart.c os/sync/spinlock.c libc/library.c tasks/tasks.c
 # Object files
 OBJS = $(SRCS:.c=.o)
 

libc/library.c

@@ -1,6 +1,15 @@
 #include "library.h"
 #include "os/driver/usart.h"
+#include "os/delay.h"
 
 void puts(const char *s) {
     usart_tx_write_string(s);
 }
+
+void usleep(unsigned int usec) {
+    delay_ms(usec);
+}
+
+void sleep(unsigned int sec) {
+    usleep(sec*1000);
+}

libc/library.h

@@ -1 +1,3 @@
 void puts(const char *s);
+void usleep(unsigned int usec);
+void sleep(unsigned int sec);

os/Makefile

@@ -1,22 +0,0 @@
-CC = arm-none-eabi-gcc
-AS = arm-none-eabi-as
-LD = arm-none-eabi-ld
-CPU = -mcpu=cortex-m4
-THUMB = -mthumb
-
-LDFLAGS = -T linker.ld
-CFLAGS = -c $(CPU) $(THUMB) -g
-
-all: main.o process.o scheduler.o
-
-main.o: main.c
-	$(CC) $(CFLAGS) main.c -o main.o
-
-scheduler.o: scheduler.c
-	$(CC) $(CFLAGS) scheduler.c -o scheduler.o
-
-process.o: process.c
-	$(CC) $(CFLAGS) process.c -o process.o
-
-clean:
-	rm -f *.elf *.o *.i

os/delay.c

@@ -1,4 +1,4 @@
-#define CLOCK_FREQUENCY 120000
+#define CLOCK_FREQUENCY 168000ULL
 
 unsigned int ms_to_ticks(unsigned int ms) {
     return ms * (CLOCK_FREQUENCY/3);
@@ -6,10 +6,9 @@ unsigned int ms_to_ticks(unsigned int ms) {
 
 void delay_routine(unsigned int delay_counter) {
     asm("mov r1, %[input]\n"
-    "loop_2:\n"
+    "delay_loop:\n"
     "subs r1, #1\n"
-    "cmp r1, #0\n"
-    "bne loop_2\n"
+    "bne delay_loop\n"
     : [input] "=r" (delay_counter));
 }
 

os/sync/spinlock.c

@@ -0,0 +1,34 @@
+// sync_primitives.c
+#include "spinlock.h"
+
+// Initialize the spinlock
+void spinlock_init(Spinlock *spinlock) {
+    spinlock->lock = 0; // Unlocked state
+}
+
+// Acquire the spinlock
+void spinlock_acquire(Spinlock *spinlock) {
+    int status;
+    do {
+        // Wait until the lock is available
+        do {
+            __asm__ volatile ("ldrex %0, [%1]"
+                              : "=&r" (status)
+                              : "r" (&spinlock->lock)
+                              : "memory");
+        } while (status != 0);
+
+        // Try to acquire the lock using strex
+        __asm__ volatile ("strex %0, %2, [%1]"
+                          : "=&r" (status)
+                          : "r" (&spinlock->lock), "r" (1)
+                          : "memory");
+    } while (status != 0); // Retry if strex failed
+}
+
+// Release the spinlock
+void spinlock_release(Spinlock *spinlock) {
+    // Use a memory barrier to ensure proper ordering
+    __asm__ volatile ("dmb" ::: "memory");
+    spinlock->lock = 0; // Release the lock
+}

os/sync/spinlock.h

@@ -0,0 +1,16 @@
+#ifndef SPINLOCK_H
+#define SPINLOCK_H
+
+#include <stdint.h>
+
+// Spinlock
+typedef struct {
+    volatile int lock;
+} Spinlock;
+
+void spinlock_init(Spinlock *spinlock);
+void spinlock_acquire(Spinlock *spinlock);
+void spinlock_release(Spinlock *spinlock);
+
+
+#endif

tasks/tasks.c

@@ -1,11 +1,13 @@
 #include "library.h"
 
 int task2(void) {
-    puts("Hello World from task 1\n");
+    puts("Hello World from task 2\n");
+    sleep(4);
     return 0;
 }
 
 int task1(void) {
-    puts("Hello World from task 2\n");
+    puts("Hello World from task 1\n");
+    sleep(2);
     return 0;
 }