Bare Minimum Setup

So my first post on here concerns setting up a minimalist environment for embedded development with the ARM toolchain (we’ll also be looking at the AVR toolchain before too long). Luckily, this is incredibly easy. Like you might imagine from the title of my blog, I’m not big on fluffy bullshit and even more so, I despise using tools that are designed to make me dependent on a certain (usually proprietary) framework. So don’t expect any IDE tutorials or examples of how to develop on Windows. I am strictly a Linux/VIM/GNU man, and I’m sure as hell not going to pay for anyones framework when I have quality tools for free. Sure, I’m probably not as “productive” as the Keil fanboys but at the very least, I know that my code isn’t dependent on a specific framework that might not be here one day. I also get the satisfaction of having complete control over my environment, which appeals to my inner control freak.

Anyways, I’m currently running Ubuntu 16.04 and I’m assuming if you are reading this, you are also on some sort of Linux distro and you know how to get vim and arm-none-eabi-gcc etc. from the terminal. However, believe it or not, I actually do all of my embedded development remotely by ssh-ing into my Raspberry Pi 3, which serves as my swiss army knife programmer/debugger via its very convenient GPIO pins and access to OpenOCD. Personally, I recommend following my lead so as not to have to buy any messy programmers (which may or may not have the nasty surprise of working only on Windows).

Luckily on the Raspbian OS that I am running on my Raspberry Pi 3, it isn’t difficult to get the arm-none-eabi toolchain setup using the usual

 sudo apt-get install arm-none-eabi-gcc

which also conveniently installs the arm-none-eabi-binutils package as well. I can’t quite recall if my RPi3 came preloaded with vim and GNU Make but it should be fairly obvious how to acquire those programs. Now in order to utilize the RPi3 as a programmer/debugger for an ARM board, we need to get a program called OpenOCD. Unfortunately, it isn’t as simple as

 sudo apt-get install openocd

since the default configuration doesn’t suit our purposes. In order to customize the package to suit our needs, we are going to have to compile it from the source, which is much less intimidating than it sounds.

In fairness, I totally ripped this setup off of Ryan at MOVr0 so credit him with the legwork on this one. First we need a few packages

 sudo apt-get install git autoconf libtool make pkg-config libusb-1.0-0 libusb-1.0-0-dev telnet  

and then to compile from the source we simply run

 git clone git://git.code.sf.net/p/openocd/code openocd

which gives us a nice little folder aptly titled “openocd” and from there we can compile


cd openocd

./bootstrap

which will download a few dependencies after which we can configure our build with


./configure --enable-maintainer-mode --enable-bcm2835gpio --enable-sysfsgpio

after which we can sit back and enjoy after we run


make -j4

and finally we can install it with


sudo make install

Now that our OpenOCD build is taken care of, we’ll step back to setting up our environment for our first project. Right now, I have an STM32-L452RE Nucleo board that I’m experimenting with and I’ve quickly discovered that STM really likes to get their hooks into you with their fancy Hardware Abstraction Library. Well the last thing I’m interested in is being abstracted away from the hardware, so I’m definitely not going to be using it. I wAnyill however succumb to the use of the CMSIS library since it is standardized across all of the ARM providers and provides all of the register definitions which saves a ton of work. Anyways, since we are still just experimenting, I usually just do something like


mkdir armfun

cd armfun

and create a few essential files right off the bat


vim makefile

vim main.c

vim aux.c

vim main.h

vim aux.h

Unfortunately, before we can even begin to write any code, we have to go to the STM website and get the “STM32CubeL4” and extract the relevant files. Personally, I just take all of the files I’ll need and put them into my directory. The files we need are in


STM32Cube_FW_L4_V1.11.0/Drivers/CMSIS/Include


STM32Cube_FW_L4_V1.11.0/Drivers/CMSIS/Device/ST/STM32L4xx

STM32Cube_FW_L4_V1.11.0/Projects/NUCLEO-L452RE-P/Templates/SW4STM32/STM32L452RE_NUCLEO

and the files we need are

 

cmsis_gcc.h  //CMSIS/Include
core_cm4.h  //CMSIS/Include
core_cmFunc.h //CMSIS/Include
core_cmInstr.h //CMSIS/Include
stm32l4xx.h    //Device/ST/STM32L4xx/Include
stm32l452xx.h   //Device/ST/STM32L4xx/Include
system_stm32l4xx.h //Device/ST/STM32L4xx/Include
system_stm32l4xx.c //Device/ST/STM32L4xx/Source/Templates
startup_stm32l452xx.s //STM32Cube_FW_L4_V1.11.0/Projects/NUCLEO-L452RE-P/Templates/SW4STM32

STM32L452RETx_FLASH.ld //STM32Cube_FW_L4_V1.11.0/Projects/NUCLEO-L452RE-P/Templates/SW4STM32/STM32L452RE_NUCLEO

 

which gives us all the files we need to utilize the CMSIS library. Take a look at the  “startup_stm32l452xx.s” file and ponder what makes this file so special as to be the lone assembly program included. Just a little hint: C requires a stack to be initialized. Can you see where the startup file does this?   In my next post, we’ll create a makefile for our mini-project and start actually writing some code.

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