This is a more advanced example that shows how to configure a timer interrupt on Raspberry Pi 2 “bare metal”. You will need IAR Embedded Workbench for ARM, and follow the Project Options steps described in the Raspberry Pi 2 Bare Metal with IAR Embedded Workbench example.
This example blinks the two on-board LEDs, so no need for extra hardware.
This is main.c
#include <stdint.h>
#include <string.h>
#include <intrinsics.h>
#include "bcm2836.h"
#define DELAYCNT 2500000
#define TIMERCNT 0x400
static void delay(uint32_t cnt);
static void timer_config(void);
volatile uint32_t toggle;
/*--------------------------------------------------*/
int main(void)
{
GPFSEL4_bit.FSEL47 = GPFSEL_OUT; // GPIO pin 47 = Output
GPFSEL3_bit.FSEL35 = GPFSEL_OUT; // GPIO pin 35 = Output
timer_config();
while (1) {
GPSET1 = GPSET_47; // Set GPIO pin 47
delay(DELAYCNT);
GPCLR1 = GPCLR_47; // Clear GPIO pin 47
delay(DELAYCNT);
}
}
/*--------------------------------------------------*/
static void delay(uint32_t cnt)
{
uint32_t i;
volatile uint32_t a;
for (i = 0; i < cnt; i++) {
a = i;
}
}
/*--------------------------------------------------*/
static void timer_config(void)
{
// Copy reset vector to address 0x0 for interrupts to work
memcpy((char*)&Reset_vector, (char*)BCM_START_ADDR,
sizeof(struct reset_struct));
// Enable timer and interrupts
Base_IRQ_enable_bit.ARM_Timer = 1;
Timer_load = TIMERCNT;
Timer_ctrl_bit.count16_23 = TIMER_CNT_23BIT;
Timer_ctrl_bit.enable = 1;
Timer_ctrl_bit.irq_enable = 1;
Timer_ctrl_bit.prescale = TIMER_PRESCALE_256;
__enable_interrupt();
}
/*--------------------------------------------------*/
__irq __arm void IRQ_Handler(void)
{
Timer_irq_clear = 1;
if (toggle) {
GPSET1 = GPSET_35;
toggle = 0;
} else {
GPCLR1 = GPCLR_35;
toggle = 1;
}
}
This is the header file bcm2836.h
#ifndef _BCM2836_H_
#define _BCM2836_H_
/* GPIO Function Select */
#define GPFSEL_IN 0x0;
#define GPFSEL_OUT 0x1;
#define GPFSEL_ALT0 0x4;
#define GPFSEL_ALT1 0x5;
#define GPFSEL_ALT2 0x6;
#define GPFSEL_ALT3 0x7;
#define GPFSEL_ALT4 0x3;
#define GPFSEL_ALT5 0x2;
#define GPSET0_ADDR 0x3F20001C
#define GPSET1_ADDR 0x3F200020
#define GPFSEL0_ADDR 0x3F200000
#define GPFSEL1_ADDR 0x3F200004
#define GPFSEL2_ADDR 0x3F200008
#define GPFSEL3_ADDR 0x3F20000C
#define GPFSEL4_ADDR 0x3F200010
#define GPCLR0_ADDR 0x3F200028
#define GPCLR1_ADDR 0x3F20002C
/* GPIO Function Select 0 */
volatile __no_init union
{
uint32_t GPFSEL0;
struct GPFSEL0_bits {
uint32_t FSEL0 : 3;
uint32_t FSEL1 : 3;
uint32_t FSEL2 : 3;
uint32_t FSEL3 : 3;
uint32_t FSEL4 : 3;
uint32_t FSEL5 : 3;
uint32_t FSEL6 : 3;
uint32_t FSEL7 : 3;
uint32_t FSEL8 : 3;
uint32_t FSEL9 : 3;
uint32_t reserved : 2;
} GPFSEL0_bit;
} @ GPFSEL0_ADDR;
/* GPIO Function Select 2 */
volatile __no_init union
{
uint32_t GPFSEL2;
struct GPFSEL2_bits {
uint32_t FSEL20 : 3;
uint32_t FSEL21 : 3;
uint32_t FSEL22 : 3;
uint32_t FSEL23 : 3;
uint32_t FSEL24 : 3;
uint32_t FSEL25 : 3;
uint32_t FSEL26 : 3;
uint32_t FSEL27 : 3;
uint32_t FSEL28 : 3;
uint32_t FSEL29 : 3;
uint32_t reserved : 2;
} GPFSEL2_bit;
} @ GPFSEL2_ADDR;
/* GPIO Function Select 3 */
volatile __no_init union
{
uint32_t GPFSEL3;
struct GPFSEL3_bits {
uint32_t FSEL30 : 3;
uint32_t FSEL31 : 3;
uint32_t FSEL32 : 3;
uint32_t FSEL33 : 3;
uint32_t FSEL34 : 3;
uint32_t FSEL35 : 3;
uint32_t FSEL36 : 3;
uint32_t FSEL37 : 3;
uint32_t FSEL38 : 3;
uint32_t FSEL39 : 3;
uint32_t reserved : 2;
} GPFSEL3_bit;
} @ GPFSEL3_ADDR;
/* GPIO Function Select 4 */
volatile __no_init union
{
uint32_t GPFSEL4;
struct GPFSEL4_bits {
uint32_t FSEL40 : 3;
uint32_t FSEL41 : 3;
uint32_t FSEL42 : 3;
uint32_t FSEL43 : 3;
uint32_t FSEL44 : 3;
uint32_t FSEL45 : 3;
uint32_t FSEL46 : 3;
uint32_t FSEL47 : 3;
uint32_t FSEL48 : 3;
uint32_t FSEL49 : 3;
uint32_t reserved : 2;
} GPFSEL4_bit;
} @ GPFSEL4_ADDR;
/* GPIO Pin Output Set 0 */
volatile __no_init uint32_t GPSET0 @ GPSET0_ADDR;
#define GPSET_0 (1<<0)
#define GPSET_1 (1<<1)
#define GPSET_2 (1<<2)
#define GPSET_3 (1<<3)
#define GPSET_4 (1<<4)
#define GPSET_5 (1<<5)
#define GPSET_6 (1<<6)
#define GPSET_7 (1<<7)
#define GPSET_8 (1<<8)
#define GPSET_9 (1<<9)
#define GPSET_10 (1<<10)
#define GPSET_11 (1<<11)
#define GPSET_12 (1<<12)
#define GPSET_13 (1<<13)
#define GPSET_14 (1<<14)
#define GPSET_15 (1<<15)
#define GPSET_16 (1<<16)
#define GPSET_17 (1<<17)
#define GPSET_18 (1<<18)
#define GPSET_19 (1<<19)
#define GPSET_20 (1<<20)
#define GPSET_21 (1<<21)
#define GPSET_22 (1<<22)
#define GPSET_23 (1<<23)
#define GPSET_24 (1<<24)
#define GPSET_25 (1<<25)
#define GPSET_26 (1<<26)
#define GPSET_27 (1<<27)
#define GPSET_28 (1<<28)
#define GPSET_29 (1<<29)
#define GPSET_30 (1<<30)
#define GPSET_31 (1<<31)
/* GPIO Pin Output Set 1 */
volatile __no_init uint32_t GPSET1 @ GPSET1_ADDR;
#define GPSET_32 (1<<0)
#define GPSET_33 (1<<1)
#define GPSET_34 (1<<2)
#define GPSET_35 (1<<3)
#define GPSET_36 (1<<4)
#define GPSET_37 (1<<5)
#define GPSET_38 (1<<6)
#define GPSET_39 (1<<7)
#define GPSET_40 (1<<8)
#define GPSET_41 (1<<9)
#define GPSET_42 (1<<10)
#define GPSET_43 (1<<11)
#define GPSET_44 (1<<12)
#define GPSET_45 (1<<13)
#define GPSET_46 (1<<14)
#define GPSET_47 (1<<15)
#define GPSET_48 (1<<16)
#define GPSET_49 (1<<17)
#define GPSET_50 (1<<18)
#define GPSET_51 (1<<19)
#define GPSET_52 (1<<20)
#define GPSET_53 (1<<21)
/* GPIO Pin Output Clear 0 */
volatile __no_init uint32_t GPCLR0 @ GPCLR0_ADDR;
#define GPCLR_0 (1<<0)
#define GPCLR_1 (1<<1)
#define GPCLR_2 (1<<2)
#define GPCLR_3 (1<<3)
#define GPCLR_4 (1<<4)
#define GPCLR_5 (1<<5)
#define GPCLR_6 (1<<6)
#define GPCLR_7 (1<<7)
#define GPCLR_8 (1<<8)
#define GPCLR_9 (1<<9)
#define GPCLR_10 (1<<10)
#define GPCLR_11 (1<<11)
#define GPCLR_12 (1<<12)
#define GPCLR_13 (1<<13)
#define GPCLR_14 (1<<14)
#define GPCLR_15 (1<<15)
#define GPCLR_16 (1<<16)
#define GPCLR_17 (1<<17)
#define GPCLR_18 (1<<18)
#define GPCLR_19 (1<<19)
#define GPCLR_20 (1<<20)
#define GPCLR_21 (1<<21)
#define GPCLR_22 (1<<22)
#define GPCLR_23 (1<<23)
#define GPCLR_24 (1<<24)
#define GPCLR_25 (1<<25)
#define GPCLR_26 (1<<26)
#define GPCLR_27 (1<<27)
#define GPCLR_28 (1<<28)
#define GPCLR_29 (1<<29)
#define GPCLR_30 (1<<30)
#define GPCLR_31 (1<<31)
/* GPIO Pin Output Clear 1 */
volatile __no_init uint32_t GPCLR1 @ GPCLR1_ADDR;
#define GPCLR_32 (1<<0)
#define GPCLR_33 (1<<1)
#define GPCLR_34 (1<<2)
#define GPCLR_35 (1<<3)
#define GPCLR_36 (1<<4)
#define GPCLR_37 (1<<5)
#define GPCLR_38 (1<<6)
#define GPCLR_39 (1<<7)
#define GPCLR_40 (1<<8)
#define GPCLR_41 (1<<9)
#define GPCLR_42 (1<<10)
#define GPCLR_43 (1<<11)
#define GPCLR_44 (1<<12)
#define GPCLR_45 (1<<13)
#define GPCLR_46 (1<<14)
#define GPCLR_47 (1<<15)
#define GPCLR_48 (1<<16)
#define GPCLR_49 (1<<17)
#define GPCLR_50 (1<<18)
#define GPCLR_51 (1<<19)
#define GPCLR_52 (1<<20)
#define GPCLR_53 (1<<21)
#define BASE_IRQ_ADDR 0x3F00B218
/* Base Interrupt enable register */
volatile __no_init union
{
uint32_t Base_IRQ_enable;
struct Base_IRQ_enable_bits {
uint32_t ARM_Timer : 1;
uint32_t ARM_Mailbox : 1;
uint32_t ARM_Doorbell_0 : 1;
uint32_t ARM_Doorbell_1 : 1;
uint32_t GPU_0_Halted : 1;
uint32_t GPU_1_Halted : 1;
uint32_t Access_err_type_1 : 1;
uint32_t Access_err_type_0 : 1;
} Base_IRQ_enable_bit;
} @ BASE_IRQ_ADDR;
#define TIMER_CNT_23BIT 1
#define TIMER_CNT_16BIT 0
#define TIMER_PRESCALE_256 2
#define TIMER_LOAD_ADDR 0x3F00B400
#define TIMER_CLR_ADDR 0x3F00B40C
#define TIMER_CTRL_ADDR 0x3F00B408
/* Timer Load register */
volatile __no_init uint32_t Timer_load @ TIMER_LOAD_ADDR;
/* Timer IRQ clear register */
volatile __no_init uint32_t Timer_irq_clear @ TIMER_CLR_ADDR;
/* Timer control register */
volatile __no_init union
{
uint32_t Timer_ctrl;
struct Timer_ctrl_bits {
uint32_t unused1 : 1;
uint32_t count16_23 : 1;
uint32_t prescale : 2;
uint32_t unused2 : 1;
uint32_t irq_enable : 1;
uint32_t unused3 : 1;
uint32_t enable : 1;
uint32_t debug_halt : 1;
uint32_t free_run : 1;
uint32_t unused4 : 6;
uint32_t free_prescale : 8;
} Timer_ctrl_bit;
} @ TIMER_CTRL_ADDR;
#define BCM_START_ADDR 0x00008000
#define BCM_VECT_ADDR 0x00000000
volatile __no_init struct reset_struct
{
uint32_t Reset;
uint32_t Undefined;
uint32_t SWI;
uint32_t Prefetch;
uint32_t Abort;
uint32_t Reserved;
uint32_t IRQ;
uint32_t FIQ;
uint32_t jump_table[7];
} Reset_vector @ BCM_VECT_ADDR;
#endif
More reading / details / thanks to:
https://github.com/dwelch67/raspberrypi
http://www.valvers.com/open-software/raspberry-pi/step01-bare-metal-programming-in-cpt1/
Tags: GPIO, Programming
Kjarvel 
4 February, 2016 at 03:38 |
Hello,
I have tried this example but interrupt is not working however timer is working fine. If just skip the __enable_interrupt(); function call then LED is working fine but when interrupt is enabled then when interrupt is called system is hang-up. It seems that something wrong with vector table. Can you help me to resolve this issue? Which steps I am missing?
Thanks
5 February, 2016 at 03:46 |
Hi, it is difficult to say what’s wrong. Perhaps you forgot to call memcpy in timer_config – the one that has the comment “Copy reset vector to address 0x0 for interrupts to work”. Or, maybe you got the addresses mixed up. I recommend using a debugger to find the issue.