The SysTick configuration ...

	ABC_IRQ_DISABLE(ABC_INT_SCHEDULER);

	/* Set the default priority level to be masked */
	CPUbasepriSet(ABC_INT_PRIORITY_MASKED);

	/* set the priority for the systems interrupts */
	MAP_IntPrioritySet(ABC_INT_SYSTICK,  ABC_INT_PRIORITY_0);
	MAP_IntPrioritySet(ABC_INT_SCHEDULER,ABC_INT_PRIORITY_SCHEDULER);
	MAP_IntPrioritySet(ABC_INT_SVCALL,   ABC_INT_PRIORITY_3);

	ABC_IRQ_ENABLE(ABC_INT_SCHEDULER);
	
	...
	
	// Configure SysTick for a periodic interrupt.
	(void) MAP_SysTickPeriodSet( (uint32_t) cpuinfo_drv_get_frequency() / SYSTICKHZ);
	(void) MAP_SysTickEnable();
	(void) MAP_SysTickIntEnable();

Where ...

	#define ABC_INT_SYSTICK       FAULT_SYSTICK
	#define ABC_INT_SCHEDULER     FAULT_PENDSV
	#define ABC_INT_SVCALL        FAULT_SVCALL

	...

	#define ABC_INT_PRIORITY_0 (0x00 << 5)
	#define ABC_INT_PRIORITY_1 (0x01 << 5)
	#define ABC_INT_PRIORITY_2 (0x02 << 5)
	#define ABC_INT_PRIORITY_3 (0x03 << 5)
	#define ABC_INT_PRIORITY_4 (0x04 << 5)
	#define ABC_INT_PRIORITY_5 (0x05 << 5)
	#define ABC_INT_PRIORITY_6 (0x06 << 5)
	#define ABC_INT_PRIORITY_7 (0x07 << 5)
			
	// The default IRQ priority of scheduler
	#define ABC_INT_PRIORITY_SCHEDULER ABC_INT_PRIORITY_6

	// The IRQ priority which is by default masked
	#define ABC_INT_PRIORITY_MASKED    ABC_INT_PRIORITY_7
	
	...
	
	CPUbasepriSet(uint32_t ui32NewBasepri)
	{
		//
		// Set the BASEPRI register
		//
		__asm("    msr     BASEPRI, r0\n"
			  "    bx      lr\n");
	}
	
	...
	
	// enable/disable all interrupts
	#define ABC_IRQ_ENABLE_ALL            (void) MAP_IntMasterEnable()
	#define ABC_IRQ_DISABLE_ALL           (void) MAP_IntMasterDisable()

	// enable/disable specific interrupts
	#define ABC_IRQ_ENABLE(IRQ_ID)        abc_irq_enable(IRQ_ID)
	#define ABC_IRQ_DISABLE(IRQ_ID)       abc_irq_disable(IRQ_ID)
	
	...
	
	ABC_STATIC_INLINE void abc_irq_enable(unsigned int irq_id)
	{
	  if (irq_id != ABC_INT_SCHEDULER)
	  {
		MAP_IntEnable(irq_id);
	  }
	  else
	  {
		MAP_IntPrioritySet(FAULT_PENDSV, ABC_INT_PRIORITY_SCHEDULER);
	  }
	}

	ABC_STATIC_INLINE void abc_irq_disable(unsigned int irq_id)
	{
	  if (irq_id != ABC_INT_SCHEDULER)
	  {
		MAP_IntDisable(irq_id);
	  }
	  else
	  {
		MAP_IntPrioritySet(FAULT_PENDSV, ABC_INT_PRIORITY_MASKED);
	  }
	}


And the Systick ISR handler ...

/***
 * Process tick of the system timer.
 ***/
void SysTick_Handler(void)
{
  ABC_IRQ_ACK(ABC_INT_SYSTICK);
    
  // call the system tick handler
  abc_sys_timer_tick();
  
  // trigger clocks
  abc_tmr_clock_trigger(CLOCK_REALTIME);

  ABC_IRQ_EOI(ABC_INT_SYSTICK);
}

Where ...

/***
 * Acknowledge interrupt
 **/
#define ABC_IRQ_ACK(irq_nr)   ABC_IRQ_DISABLE_ALL 

/***
 * End of interrupt
 **/
#define ABC_IRQ_EOI(irq_id)  if (0 == abc_spin_irq_count) { ABC_IRQ_ENABLE_ALL; }