Bare Medal on BCM2835 and BCM2836

A few days ago, I have tried to write bare medal program but failed. Now I find that the main mistake is that I have mistake the address of GPIO of BCM 2835(Raspberry Pi 1 for which the sample code is desined ) and BCM2836(Raspberry Pi 2 which I am using).

Refrence: dwelch67

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Firstly, the base address of GPIO is changed.

Address of RPi BCM2835: 0x20000000

Address of RPi BCM2836: 0x3f000000

Let us make it more easier

Create two file BCM2835.h and BCM2836.h to recode the macro define.

BCM2835.h

#define PBASE 0x20000000

BCM2836.h

#define PBASE 0x3f000000

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Then in the code which control your used to control the peripheral, like periph.c, add the following code:

#ifdef RPI2
#include "BCM2836.h" //Raspberry Pi 2
#else
#include "BCM2835.h" //Raspberry Pi 1
#endif

//Ther other macro looks like this:
#define ARM_TIMER_CTL   (PBASE + 0x0000B408)

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At last, we could modify our Makefile to generate two kernel image:

1. kernel.img : for Raspberry Pi 1, BCM2835
   
2. Kernel7.img : for Raspberry Pi 2, BCM2836
   

To do this, you could add -DRpi2 in your compile cmd to add the macro define

$(ARMGNU)-gcc $(COPS) -c periph.c -o periph7.o -DRPI2  

And this is why your /boot/ directory has both kernel.img and kernel7.img.

The official has already consider the two situations.