Add base code

.gdbinit

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+target remote :1234
+b main

.gitignore

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+# Prerequisites
+*.d
+
+# Object files
+*.o
+*.ko
+*.obj
+*.elf
+
+# Linker output
+*.ilk
+*.map
+*.exp
+
+# Precompiled Headers
+*.gch
+*.pch
+
+# Libraries
+*.lib
+*.a
+*.la
+*.lo
+
+# Shared objects (inc. Windows DLLs)
+*.dll
+*.so
+*.so.*
+*.dylib
+
+# Executables
+*.exe
+*.out
+*.app
+*.i*86
+*.x86_64
+*.hex
+
+# Debug files
+*.dSYM/
+*.su
+*.idb
+*.pdb
+
+# Kernel Module Compile Results
+*.mod*
+*.cmd
+.tmp_versions/
+modules.order
+Module.symvers
+Mkfile.old
+dkms.conf
+
+# GDB
+.gdb_history

Makefile

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+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 = $(CPU) $(THUMB)
+
+QEMU = qemu-system-arm
+BOARD = netduino2
+
+# Output file
+TARGET = main.elf
+# Source files
+SRCS = os/main.c os/process.c os/scheduler.c os/alloc.c tasks/library.c tasks/tasks.c
+# Object files
+OBJS = $(SRCS:.c=.o)
+
+debug: CFLAGS += -g
+debug: all
+
+run: debug
+	$(QEMU) -M $(BOARD) -nographic -kernel $(TARGET)
+
+gdb: debug
+	$(QEMU) -M $(BOARD) -nographic -kernel $(TARGET) -s -S
+
+# Default target to build the ELF file
+all: $(TARGET)
+
+$(TARGET): $(OBJS) startup.o
+	$(LD) $(LDFLAGS) startup.o $(OBJS) -o $(TARGET)
+
+startup.o: startup.s
+	$(AS) $(CPU) -g startup.s -o startup.o
+
+# Rule to compile source files into object files
+%.o: %.c
+	$(CC) $(CFLAGS) -c $< -o $@
+
+clean:
+	rm -f *.elf *.o *.i
+	rm -f os/*.o tasks/*.o

libc/library.c

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+#include "library.h"
+
+volatile unsigned int *const USART1_PTR = (unsigned int *)0x40011004;
+
+void puts(const char *s) {
+    while(*s != '\0') { /* Loop until end of string */
+        *USART1_PTR= (unsigned int)(*s); /* Transmit char */
+        s++; /* Next char */
+    }
+}

libc/library.h

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+void puts(const char *s);

linker.ld

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+ENTRY(_start)
+
+SECTIONS
+{
+    /* text section (code)*/
+    .text : { *(.text*) }
+    /* data section, initialized variables */
+    .data : { *(.data) }
+    ram_start = 0x20000000;
+    /* bss section, uninitialized variables */
+    .bss : { *(.bss*) }
+    /* stack section */
+    /* The stack is placed at the end of the RAM */
+    stack_top = 0x2001ffff;
+}

os/Makefile

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+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/alloc.c

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+#include "alloc.h"
+#include "stdint.h"
+
+void* *first_mem_avail = (void*) 0x20000000;
+
+void init_allocator() {
+    *first_mem_avail = (void*) 0x20000000 +sizeof(void*);
+}
+
+void* malloc(size_t size) {
+    void* block = *first_mem_avail;
+    *first_mem_avail += size;
+    return block;
+}

os/alloc.h

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+#include <stddef.h>
+
+void init_allocator();
+void* malloc (size_t size);

os/main.c

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+#include "process.h"
+#include "scheduler.h"
+#include "alloc.h"
+
+extern int task1(void);
+extern int task2(void);
+
+int main(void) {
+    init_allocator();
+    ProcessTable *ptable;
+    create_process_table(&ptable);
+
+    create_process(ptable, task1);
+    create_process(ptable, task2);
+
+    run(ptable);
+}