#include <stdint.h>

enum execution_mode {
  MODE_USER = 0x10,
  MODE_FIQ = 0x11,
  MODE_IRQ = 0x12,
  MODE_SUPERVISOR = 0x13,
  MODE_MONITOR = 0x16,
  MODE_ABORT = 0x17,
  MODE_HYPERVISOR = 0x1a,
  MODE_UNDEFINED = 0x1b,
  MODE_SYSTEM = 0x1f,
};

inline static uint32_t read_CPSR(void)
{
  uint32_t CPSR;
  // get content of current program status register
  asm("mrs %0, cpsr" : "=r" (CPSR) ::);
  
  return CPSR;
}

inline static enum execution_mode read_processor_mode(void)
{
  /* lowest 5 bits indicate processor mode */
  return read_CPSR() & 0x1f;
}

inline static void set_system_mode(void)
{
  uint32_t CPSR = read_CPSR();

  CPSR = (CPSR >> 5) << 5;

  CPSR |= MODE_SYSTEM;
  
  asm("msr cpsr, %0" :: "r" (CPSR) : "memory");  
}