I wrote a very simple kernel years ago, and ran it on a 386. I haven't done bare metal programming in years, but in broad terms you need to write some assembler code that will:
disable interrupts during the boot process
if the Pi has a memory controller, you'll need to set that up
set up a timer tick
configure the interrupt controller
set up a stack so ...
I haven't looked at your code in depth, but it seems to me you're on the right track. Make sure that:
The _start symbol is indeed the one used when compiling & linking your assembly file and your C file (and that main() isn't used instead)
When calling main(), you need to use the C calling convention:
push on the stack the address of the instruction ...
Assembly is a programming language, and, like other programming languages, you have plain text source codes that can be edited by all text editors out there.
The confusion comes from the fact that, as it is the lowest level programming language just above machine language, other programming language's compilers will generate assembly source-code from their ...
The root problem is that the activity LED moved from being attached to gpio 16 to being attached to gpio 47 on the B+. You need to update the code to reflect that change.
There are a number of changes you need to make. It is more than just changing 16 to 47. Gpio 47 is controlled by different registers.
See this thread on raspberrypi.org which covers ...
I have not tried it, but there is a binutils-multiarch package "used to manipulate binary and object files that may have been created on other architectures". It includes an objdump which from the looks of things will replace the existing one. The other files are listed here.
So, worth trying:
apt-get install binutils-multiarch
And seeing if the new ...
You need to tell gcc the architecture when just assembling like this. So gcc -march=native -o test test.s tells it to assemble for your native architecture (arm on a RPi).
This will yield link errors about multiple definitions of _start and crt1.o. Gcc expects to link in the C runtime which actually provides _start normally and that then calls main. You can ...
I would recommend taking a look at this site http://www.makeuseof.com/tag/emulate-raspberry-pi-pc/ which describes how to emulate the original raspberry pi on a pc. You then should be able to debug and run assembly code on the emulated raspberry pi that you created.
Unfortunately things are not as easy as you described. All the applications you gave as an example (a compiler, an editor, an interpreter, etc) are quite complicated and they are not only doing computation but also interact quite heavily with the OS. They need a way to use files, interact with user (like keyboard input, screen output), expect a concept of "...
Try this instead:
Also, the x86 experience is a bit different. It may be applicable to general ARM bare metal OS programming. But for Pi, sorry it is the gpu start first and set up quite a bit before your OS (?) code.
The main problem you might encounter is the C libraries and prologue code. It's started before your own code starts executing and sets up the stack, the heap and does plenty of other helpful things. However, when you're trying to program for bare metal you don't have any OS running below you and you'd better to avoid calling these functions. In order to do ...
Okay, I figured it out myself...
The first ldr actually loads the address of the variable. And so to have the value of pattern in the register (rather than the address), I still have to load the value at the address into the register.
Also check here
I'm not surprised you couldn't find any information.
The BCM2836 is a SoC not a CPU. As far as you are concerned the BCM2836 is identical to the BCM2835 except for the different ARM CPU.
The main user CPU used on the Pi 2 is an ARM Cortex A7 with four cores.
If you search for BCM2835 and the ARM CPU you'll find all the information you could need.
On the Pis with the 40 pin expansion header (except Pi3)
the power LED (red) is connected to GPIO 35 (not present on the Pi Zero)
the activity LED (green) is connected to GPIO 47
Pi3 uses a GPIO expander to drive the LEDs which can only be accessed from the VPU.
After doing a bit of research, as well as testing things out, I discovered that I was misinterpreting what I was hearing about physical pin numbers. The GPIO Pin numbers listed in official pinouts as GPIO## or BCM## do actually correspond to the raw GPIO pin numbers for the Broadcom SoC.
You may be able to do what you want with the debugger gdb.
Compile and link a small test program.
int main(int argc, char *argv)
for (i=0; i<10; i++) printf("%d\n", i*i);
gcc -o q q.c
Enter the commands
and then si to single step
┌──Register group: ...
You need to check your country's laws regarding wireless transmission systems. You need to make sure that you're not exceeding any limits in terms of, for example, power transmission, and that you are not operating in a band for which you have not been granted permission. The bottom line is: before you start building anything, research and make sure that ...
Ok found the solution. There were some coding issues.
This code is working now:
@ Base adress for gpio controller
ldr r0, =0x20200000
@ Set GPIO 24 as output
mov r2, #0x01
lsl r2, #0x0C
str r2, [r0, #0x08]
@ Set GPIO 13 as input
mov r1, #0x00
str r1, [r0, #0x04]
@ I/O masks
mov r2, #0x01
lsl r2, #0x0D
mov r3, #...
First of all to clear up ambiguities:
Aarch32/Aarch64: These are two main Instruction Set Architectures for ARM (Advanced RISC Machine) architecture processors.
Armv7-A/Armv8-A: These are the most common specifications of ARM hardware as of today. They specify what instructions are to be supported.
Answering my points:
I would like to know if it is ...
You can always run 32 bit programs/operating systems on a 64 bit architecture. That is downstream compatible. You cannot run 64 bit programs on a 32 bit architecture, of course. So it is no problem to compile 32 programs on a Raspberry Pi 4B in particular if you use the 32 bit operating system Raspbian (running on 64 bit architecture). Raspbian is a 32 bit ...
do you say that it does not matter if the the processor is 32 or 64 bit because if I have a 32-bit OS running on it, 32 bit programs will run just fine on it?
Yes; this is also true for x86-64: You can run 32-bit software on an ISA compatible 64-bit machine. If you've ever had to do that though, it was probably in the context of a 64-bit operating system. ...
The solution lies in the config.txt.
After reading many forums and the RPi site, there is a config option called disable_commandline_tags.
If it is not set or is set to 0 in config.txt, ATAGS is loaded by start.elf starting at 0x100. My kernel was also using kernel_old=1, which starts loading at 0x0.
The ATAGs entry was overwriting a piece of the kernel....
You are running this under userland Linux.
Userland address spaces are virtual address spaces which bear no relationship to physical (hardware address spaces).
The Memory Management Unit (MMU) maps virtual addresses to physical addresses.
You need to tell your program to allow access to physical address 0x3F000000.
In C you would use mmap. I have no ...
I expect your terminology is incorrect.
If you want to control interrupts you will either have to go bare metal or write a Linux kernel driver.
If you use Raspbian from userland you can not "control" interrupts. However you can request a callback when an interrupt happens.
Do you want to use interrupts to control peripherals? To do what?
While there is a full schematics of the B, rev2 on Raspberrypi.org only some "Reduced Schematics" for the B+ are available. This is stripped down to the absolute minimum, but it is at least possible to figure out the pin numbering on the GPIO expansion header.
Another nice spot to visit is elinux which is updated with information of the different pin ...