Question: arm cortex a9

[Arnold1]

Hi,

great work. how much effort is it to port the led blink example to arm cortex a9 - bare metal?

quick question to your project. why is your main.rs a staticlib? how does it create the executable .ldf?

Thanks, A

[antoinealb]

Hello Arnold, I don't know how long it would take, but you would need to write a few different things:

• The driver part, provided by Texas' Tivaware in this example, but you can also write your own using your datasheet.
• The minimum runtime responsible for initializing the RAM, copying the vector table, etc. This is usually called a crt0, you can find the one I am using here: https://github.com/antoinealb/rust-demo-cortex-m4/blob/master/LM4F_startup.c
• You should also adapt the build system to your target platform. This would require a linker script (specific to your chip) and an LLVM machine file for the Cortex A9 variant you want to use.

My main.rs is a static library because I want to link it using arm-none-eabi-ld (here: https://github.com/antoinealb/rust-demo-cortex-m4/blob/master/Makefile#L140) with Tivaware and it was the easiest option. Maybe there is a way to link with LLVM, but I am not familiar with it.

I don't know which ldf file you are talking about ?

Antoine

[Arnold1]

thanks for your quick reply.

sorry i mean .elf file, the following project uses arm cortex m4 and creates a elf file to be the executable: https://github.com/neykov/armboot

i have a linker script (ld file) and startup.s file...

[antoinealb]

So once you assembled your startup.s file you will have a startup.o file. Using Rust's compiler you can compile your rust main to a main.o file by telling it that you want to create a static library.

Then, using arm-none-eabi-ld (GCC's arm linker) you link together your .o files to create an ELF file. The linker script is used at this step to explain where to put variables in RAM, functions in ROM, etc. For example, here is my command to do this (from the Makefile): arm-none-eabi-ld -T LM4F.ld --gc-sections -o main.axf LM4F_startup.o main.o tivaware/driverlib/gcc/libdriver.a

Small breakdown:

• -T LM4F.ld tells the linker which script to use.
• --gc-sections removes unused functions. This can be used with gcc options to remove unused code, reducing memory footprint.
• -o main.axf puts the resulting ELF in main.axf
• Then comes all the object files to link in this binary.

Hops that helps

[Arnold1]

thanks for the info.

first i need to build the rust cross compiler.

do you know how my rust target description (.json) would look like? im not sure about the llvm-target, the rest should be the same...

here is the compiler i use:

arm-xilinx-eabi-gcc -v
Using built-in specs.
COLLECT_GCC=arm-xilinx-eabi-gcc
COLLECT_LTO_WRAPPER=/opt/Xilinx/SDK/2015.1/gnu/arm/lin/bin/../libexec/gcc/arm-xilinx-eabi/4.9.1/lto-wrapper
Target: arm-xilinx-eabi
Configured with: /scratch/cltang/xilinx/eabi/src/gcc-4.9-2014.11/configure --build=i686-pc-linux-gnu --host=i686-pc-linux-gnu --target=arm-xilinx-eabi --enable-threads --disable-libmudflap --disable-libssp --disable-libstdcxx-pch --with-arch=armv7-a --with-cpu=cortex-a9 --with-float=softfp --with-fpu=neon-fp16 --disable-multilib --with-gnu-as --with-gnu-ld --with-specs='%{save-temps: -fverbose-asm} -D__CS_SOURCERYGXX_MAJ__=2014 -D__CS_SOURCERYGXX_MIN__=11 -D__CS_SOURCERYGXX_REV__=31' --enable-languages=c,c++ --disable-shared --enable-lto --with-newlib --with-pkgversion='Sourcery CodeBench Lite 2014.11-31' --with-bugurl=https://s...content-available-to-author-only...r.com/GNUToolchain/ --disable-nls --prefix=/opt/codesourcery --with-headers=yes --with-sysroot=/opt/codesourcery/arm-xilinx-eabi --with-build-sysroot=/scratch/cltang/xilinx/eabi/install/opt/codesourcery/arm-xilinx-eabi --with-gmp=/scratch/cltang/xilinx/eabi/obj/pkg-2014.11-31-arm-xilinx-eabi/xilinx-2014.11-31-arm-xilinx-eabi.extras/host-libs-i686-pc-linux-gnu/usr --with-mpfr=/scratch/cltang/xilinx/eabi/obj/pkg-2014.11-31-arm-xilinx-eabi/xilinx-2014.11-31-arm-xilinx-eabi.extras/host-libs-i686-pc-linux-gnu/usr --with-mpc=/scratch/cltang/xilinx/eabi/obj/pkg-2014.11-31-arm-xilinx-eabi/xilinx-2014.11-31-arm-xilinx-eabi.extras/host-libs-i686-pc-linux-gnu/usr --with-isl=/scratch/cltang/xilinx/eabi/obj/pkg-2014.11-31-arm-xilinx-eabi/xilinx-2014.11-31-arm-xilinx-eabi.extras/host-libs-i686-pc-linux-gnu/usr --with-cloog=/scratch/cltang/xilinx/eabi/obj/pkg-2014.11-31-arm-xilinx-eabi/xilinx-2014.11-31-arm-xilinx-eabi.extras/host-libs-i686-pc-linux-gnu/usr --disable-libgomp --disable-libitm --disable-libatomic --disable-libssp --enable-poison-system-directories --with-build-time-tools=/scratch/cltang/xilinx/eabi/install/opt/codesourcery/arm-xilinx-eabi/bin --with-build-time-tools=/scratch/cltang/xilinx/eabi/install/opt/codesourcery/arm-xilinx-eabi/bin SED=sed
Thread model: single
gcc version 4.9.1 (Sourcery CodeBench Lite 2014.11-31)

target description:

{
    "arch": "arm",
    "cpu": "cortex-a9",
    "data-layout": "e-m:e-p:32:32-i1:8:32-i8:8:32-i16:16:32-i64:64-v128:64:128-a:0:32-n32-S64",
    "disable-redzone": true,
    "executables": true,
    "llvm-target": "arm-unknown-eabi",  or armv7a-arm-none-eabi ????
    "morestack": false,
    "os": "none",
    "relocation-model": "static",
    "target-endian": "little",
    "target-pointer-width": "32"
}

[antoinealb]

I think the llvm target should be "armv7a-arm-none-eabi" but I am not sure. Perhaps the easiest is to try ? :)