cpu/cc2538: vector table address and alignment

Enforce the 512-byte vector table alignment and set the
VTOR register to the actual address of the vector table.

cpu/cc2538/cpu.c

@@ -17,6 +17,8 @@
  * @}
  */
 
+#include <assert.h>
+
 #include "cpu.h"
 
 #define BIT(n)          ( 1UL << (n) )
@@ -32,6 +34,8 @@
 
 #define CLOCK_STA_MASK ( OSC32K | OSC )
 
+extern const void *interrupt_vector[];
+
 static void cpu_clock_init(void);
 
 /**
@@ -40,7 +44,8 @@ static void cpu_clock_init(void);
 void cpu_init(void)
 {
     /* configure the vector table location to internal flash */
-    SCB->VTOR = FLASH_BASE;
+    assert((uintptr_t)&interrupt_vector % CC2538_VTOR_ALIGN == 0);
+    SCB->VTOR = (uintptr_t)&interrupt_vector;
 
     /* Enable the CC2538's more compact alternate interrupt mapping */
     SYS_CTRL->I_MAP = 1;

cpu/cc2538/include/cc2538.h

@@ -809,6 +809,8 @@ typedef volatile uint32_t cc2538_reg_t; /**< Least-significant 32 bits of the IE
 #define XOSC32M_FREQ                32000000 /**< 32 MHz external oscillator/clock frequency */
 #define RCOSC16M_FREQ               16000000 /**< 16 MHz internal RC oscillator frequency */
 
+#define CC2538_VTOR_ALIGN                512 /**< CC2538 Vector Table alignment */
+
 #ifdef __cplusplus
 }
 #endif

cpu/cc2538/startup.c

@@ -165,7 +165,7 @@ void isr_dma(void)           __attribute__ ((weak, alias("dummy_handler")));
 void isr_dmaerr(void)        __attribute__ ((weak, alias("dummy_handler")));
 
 /* interrupt vector table */
-__attribute__ ((section(".vectors")))
+__attribute__ ((section(".vectors"), aligned(CC2538_VTOR_ALIGN)))
 const void *interrupt_vector[] = {
     /* Stack pointer */
     (void*) (&_estack),             /* pointer to the top of the empty stack */