Work on scs.h register and also nvic.h.

ARM Interrupt API (see nvic.h).
ARM SysTick API (see systick.h).
Example using both Interrupt and SysTick and blink LED1/2/3 see systickdemo.c.

examples/lpc43xx/hackrf-jellybean/systick/Makefile

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+##
+## This file is part of the libopencm3 project.
+##
+## Copyright (C) 2012 Benjamin Vernoux <titanmkd@gmail.com>
+##
+## This library is free software: you can redistribute it and/or modify
+## it under the terms of the GNU Lesser General Public License as published by
+## the Free Software Foundation, either version 3 of the License, or
+## (at your option) any later version.
+##
+## This library is distributed in the hope that it will be useful,
+## but WITHOUT ANY WARRANTY; without even the implied warranty of
+## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+## GNU Lesser General Public License for more details.
+##
+## You should have received a copy of the GNU Lesser General Public License
+## along with this library.  If not, see <http://www.gnu.org/licenses/>.
+##
+
+BINARY = systickdemo
+
+LDSCRIPT = ../jellybean-lpc4330.ld
+
+include ../../Makefile.include

examples/lpc43xx/hackrf-jellybean/systick/README

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+------------------------------------------------------------------------------
+README
+------------------------------------------------------------------------------
+
+This program exercises the SysTick Interrupt of ARM CortexM4 on Jellybean's LPC43xx.
+It also enable Cycle Counter to be used for accurate delay independant from Clock Frequency.
+The Demo Use Cycle Counter and SysTick Interrupt to compute number of cycles executed per second.
+The result is LED1/2 & 3 Blink with an accurate 1s Period (using SysTick) (Checked visualy and with Oscilloscope).

examples/lpc43xx/hackrf-jellybean/systick/systickdemo.c

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+/*
+ * This file is part of the libopencm3 project.
+ *
+ * Copyright (C) 2012 Benjamin Vernoux <titanmkd@gmail.com>
+ *
+ * This library is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Lesser General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public License
+ * along with this library.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <libopencm3/lpc43xx/gpio.h>
+#include <libopencm3/lpc43xx/scu.h>
+#include <libopencm3/lpc43xx/cgu.h>
+#include <libopencm3/lpc43xx/nvic.h>
+#include <libopencm3/lpc43xx/systick.h>
+#include <libopencm3/cm3/scs.h>
+
+#include "../jellybean_conf.h"
+
+/* Global counter incremented by SysTick Interrupt each millisecond */
+volatile u32 g_ulSysTickCount;
+u32 g_NbCyclePerSecond;
+
+void gpio_setup(void)
+{
+	/* Configure all GPIO as Input (safe state) */
+	GPIO0_DIR = 0;
+	GPIO1_DIR = 0;
+	GPIO2_DIR = 0;
+	GPIO3_DIR = 0;
+	GPIO4_DIR = 0;
+	GPIO5_DIR = 0;
+	GPIO6_DIR = 0;
+	GPIO7_DIR = 0;
+
+	/* Configure SCU Pin Mux as GPIO */
+	scu_pinmux(SCU_PINMUX_LED1, SCU_GPIO_FAST);
+	scu_pinmux(SCU_PINMUX_LED2, SCU_GPIO_FAST);
+	scu_pinmux(SCU_PINMUX_LED3, SCU_GPIO_FAST);
+	
+	scu_pinmux(SCU_PINMUX_EN1V8, SCU_GPIO_FAST);
+	
+	scu_pinmux(SCU_PINMUX_BOOT0, SCU_GPIO_FAST);
+	scu_pinmux(SCU_PINMUX_BOOT1, SCU_GPIO_FAST);
+	scu_pinmux(SCU_PINMUX_BOOT2, SCU_GPIO_FAST);
+	scu_pinmux(SCU_PINMUX_BOOT3, SCU_GPIO_FAST);
+
+	/* Configure SSP1 Peripheral (to be moved later in SSP driver) */
+	scu_pinmux(SCU_SSP1_MISO, (SCU_SSP_IO | SCU_CONF_FUNCTION5));
+	scu_pinmux(SCU_SSP1_MOSI, (SCU_SSP_IO | SCU_CONF_FUNCTION5));
+	scu_pinmux(SCU_SSP1_SCK,  (SCU_SSP_IO | SCU_CONF_FUNCTION1));
+	scu_pinmux(SCU_SSP1_SSEL, (SCU_SSP_IO | SCU_CONF_FUNCTION1));
+
+	/* Configure GPIO as Output */
+	GPIO2_DIR |= (PIN_LED1|PIN_LED2|PIN_LED3); /* Configure GPIO2[1/2/8] (P4_1/2 P6_12) as output. */
+	GPIO3_DIR |= PIN_EN1V8; /* GPIO3[6] on P6_10  as output. */
+}
+
+void systick_setup(void)
+{
+	u32 systick_reload_val;
+	g_ulSysTickCount = 0;
+
+	/* Disable IRQ globally */
+	asm volatile ("cpsid i");
+
+	/* Set processor Clock as Source Clock */
+	systick_set_clocksource(STK_CTRL_CLKSOURCE);
+
+	/* Get SysTick calibration value to obtain by default 1 tick = 10ms */
+	systick_reload_val = systick_get_calib();
+	/*
+     * Calibration seems wrong on LPC43xx(TBC) for default Freq it assume System Clock is 12MHz but it is 12*8=96MHz
+	 * Fix the Calibration value bu multiplication by 8
+     */
+	systick_reload_val = (systick_reload_val*8);
+
+	/* To obtain 1ms per tick just divide by 10 the 10ms base tick and set the reload */
+	systick_reload_val = systick_reload_val/10;
+	systick_set_reload(systick_reload_val);
+
+	systick_interrupt_enable();
+
+	/* Start counting. */
+	systick_counter_enable();
+
+	/* Set SysTick Priority to maximum */
+	nvic_set_priority(NVIC_SYSTICK_IRQ, 0xFF);
+
+	/* Enable IRQ globally */
+	asm volatile ("cpsie i");
+}
+
+void scs_dwt_cycle_counter_enabled(void)
+{
+	SCS_DEMCR |= SCS_DEMCR_TRCENA;
+	SCS_DWT_CTRL  |= SCS_DWT_CTRL_CYCCNTENA;
+}
+
+u32 sys_tick_get_time_ms(void)
+{
+    return g_ulSysTickCount;
+}
+
+u32 sys_tick_delta_time_ms(u32 start, u32 end)
+{
+	#define MAX_T_U32 ((2^32)-1)
+    u32 diff;
+
+    if(end > start)
+    {
+        diff=end-start;
+    }else
+    {
+        diff=MAX_T_U32-(start-end)+1;
+    }
+    
+    return diff;
+}
+
+void sys_tick_wait_time_ms(u32 wait_ms)
+{
+    u32 start, end;
+    u32 tickms;
+
+    start = sys_tick_get_time_ms();
+
+    do
+    {
+        end = sys_tick_get_time_ms();
+        tickms = sys_tick_delta_time_ms(start, end);
+    }while(tickms < wait_ms);
+}
+
+/* Called each 1ms/1000Hz by interrupt
+ 1) Count the number of cycle per second.
+ 2) Increment g_ulSysTickCount counter.
+*/
+void sys_tick_handler(void)
+{
+	if(g_ulSysTickCount==0)
+	{
+		/* Clear Cycle Counter*/
+		SCS_DWT_CYCCNT = 0;
+	}else if(g_ulSysTickCount==1000)
+	{
+		/* Capture number of cycle elapsed during 1 second */
+		g_NbCyclePerSecond = SCS_DWT_CYCCNT;
+	}
+
+	g_ulSysTickCount++;
+}
+
+int main(void)
+{
+	systick_setup();
+
+	gpio_setup();
+
+	/* SCS & Cycle Counter enabled (used to count number of cycles executed per second see g_NbCyclePerSecond */
+	scs_dwt_cycle_counter_enabled();
+
+	while (1) 
+	{
+		gpio_set(PORT_LED1_3, (PIN_LED1|PIN_LED2|PIN_LED3)); /* LEDs on */
+
+		sys_tick_wait_time_ms(500);
+
+		gpio_clear(PORT_LED1_3, (PIN_LED1|PIN_LED2|PIN_LED3)); /* LED off */
+
+		sys_tick_wait_time_ms(500);
+	}
+
+	return 0;
+}