ARMv7-A Bare Bones: Difference between revisions

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Line 1: {{TutorialExplain}} {{BeginnersWarning}} {{Rating\|1}}{{Kernel designs}} In this tutorial, weyou will write a basic ARM kernel and boot it. WeYou will target the ARM Versatile Express development board for the Cortex-A15. ~~<b>You should read [[Getting Started]] and [[Beginner Mistakes]]</b> before~~ ~~starting this tutorial.~~ == Rationale == === ~~<b>~~Why ARMv7-A?~~</b>~~ === ARMv7 is likely the last purely 32-bit iteration of the ARM architecture, so processors based on it are likely to be supported the longest. The 'A' profile is Line 15 ⟶ 14: most interest to OS developers. === ~~<b>~~Why the Cortex-A15?~~</b>~~ === Largely because it's the most powerful ARMv7-A processor supported by QEMU, and it also has its own development board. === ~~<b>~~Why the Versatile Express?~~</b>~~ === This board was designed by ARM Holdings as a prototyping board, so it makes sense to target a relatively neutral platform built with the Cortex-A15 in mind. Line 25 ⟶ 24: == Toolchain == ~~We'll~~You will be using the [[GNU ~~toolchain~~Toolchain]] for this, so go read [[GCC Cross-Compiler]] if you haven't already. The target platform is <code>arm-none-eabi</code>. You will need at least [[GAS]], [[GCC]], and [[LD]], but it is also suggested to have [[GDB]], [[Objcopy]], and [[Objdump]]. ~~least <code>as</code>, <code>gcc</code>, and <code>ld</code>, but I suggest also~~ ~~having <code>gdb</code>, <code>objcopy</code>, and <code>objdump</code>.~~ == Code == Line 34 ⟶ 32: _start.arm: <syntaxhighlight lang="asm"> ~~<pre>~~ .global _start _start: Line 42 ⟶ 40: b 1b .size _start, . - _start </syntaxhighlight> ~~</pre>~~ start.c: Line 48 ⟶ 46: <syntaxhighlight lang="c"> #include <stdint.h> #define UART0_BASE 0x1c090000 void start() { { (volatile uint32_t )(UART0_BASE) = 'A'; } Line 58 ⟶ 55: linker.ld: <syntaxhighlight lang="c"> ~~<pre>~~ ENTRY(_start) Line 78 ⟶ 75: STACK_TOP = .; } </syntaxhighlight> ~~</pre>~~ == Building and Running == <syntaxhighlight lang="bash"> ~~<pre>~~ $ arm-none-eabi-as -march=armv7-a -mcpu=cortex-a15 _start.arm -o _start.o $ arm-none-eabi-gcc -ffreestanding -Wall -Wextra -Werror -c start.c -o start.o $ arm-none-eabi-ld -T linker.ld _start.o start.o -o kernel.elf $ qemu-system-arm -M vexpress-a15 -cpu cortex-a15 -kernel kernel.elf -nographic </syntaxhighlight> ~~</pre>~~ ~~== Resources ==~~ ~~It's a lot of material, but these are invaluable references for developing on ARM platforms.~~ == See Also == === External Links === [http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.subset.boards.express/index.html ARMv7 Cortex-A Series Programmer's Guide] * [http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.ddi0406c/index.html ARMv7-A Architecture Reference Manual] Line 100 ⟶ 95: [[Category:ARM]] [[Category:Bare bones tutorials]]