Add SysTick handler

Makefile

@@ -3,6 +3,11 @@
 APPLICATION ?= blinky
 
 PLATFORM ?= nrf52
+
+ifneq "$(findstring $(PLATFORM), nrf52)" ""
+CORE = cm4
+endif
+
 TARGET_FILE ?= $(APPLICATION).elf
 
 CC = $(CROSS_COMPILE)gcc
@@ -25,6 +30,7 @@ C_SRCS += $(wildcard $(SRC_DIR)/application/$(APPLICATION)/*.c)
 C_OBJS = $(patsubst $(SRC_DIR)%,$(OBJ_DIR)%,$(patsubst %.c,%.c.o,$(C_SRCS)))
 
 CC_SRCS = $(wildcard $(SRC_DIR)/*.cc)
+CC_SRCS += $(wildcard $(SRC_DIR)/platform/$(CORE)/*.cc)
 CC_SRCS += $(wildcard $(SRC_DIR)/platform/$(PLATFORM)/*.cc)
 CC_SRCS += $(wildcard $(SRC_DIR)/application/$(APPLICATION)/*.cc)
 CC_OBJS = $(patsubst $(SRC_DIR)%,$(OBJ_DIR)%,$(patsubst %.cc,%.cc.o,$(CC_SRCS)))

src/platform/cm4/SystemTick.cc

@@ -0,0 +1,35 @@
+extern "C" {
+    #include "nrf52.h"
+}
+
+#include "platform/cm4/SystemTick.h"
+#include "platform/nrf52/InterruptGuardian.h"
+
+using namespace pinetime::platform::cm4;
+using namespace pinetime::platform::nrf52;
+
+SystemTick::SystemTick()
+    : InterruptHandler(InterruptGuardian::Nrf52IrqN::SYS_TICK_IRQ)
+    , sys_tick(0)
+{
+}
+
+void SystemTick::handle()
+{
+    this->sys_tick++;
+}
+
+void SystemTick::enable()
+{
+    SysTick_Config(SystemCoreClock / 1000);
+}
+
+void SystemTick::disable()
+{
+    SysTick->CTRL = 0;
+}
+
+uint32_t SystemTick::tick()
+{
+    return this->sys_tick;
+}

src/platform/cm4/SystemTick.h

@@ -0,0 +1,23 @@
+#ifndef __PLATFORM_CM4_SYSTEMTICK_H__
+#define __PLATFORM_CM4_SYSTEMTICK_H__
+
+#include "platform/nrf52/InterruptHandler.h"
+
+namespace pinetime::platform::cm4 {
+
+class SystemTick : public pinetime::platform::nrf52::InterruptHandler
+{
+    public:
+        SystemTick();
+        void handle();
+        void enable();
+        void disable();
+        uint32_t tick();
+
+    private:
+        uint32_t sys_tick;
+};
+
+}
+
+#endif