Blink demo and pocket-sized register library for stm32 ARM chip, in pure Assembly Language

(Initially developed on stm32f4 series hardware)

This is intended to be an intro for general-case Embedded ARM Assembly Programming

These demos were initially coded on a stm32f401re CPU, (Cortex M4) shipped on a Nucleo-F-401RE board with an LED, sold by ST Microelectronics

• https://www.st.com/en/microcontrollers-microprocessors/stm32f4-series.html
• https://www.st.com/en/microcontrollers-microprocessors/stm32f401.html
• https://www.st.com/en/evaluation-tools/nucleo-f401re.html
• https://os.mbed.com/platforms/ST-Nucleo-F401RE/

It now also supports Nucleo-L476RG, which is stm32l476 cpu based)

There are now multiple choices for C-code development, for ARM chips. "Keil", or STM's "CubeIDE" are just two of them. However, they arent friendly to Assembly Language development. Keil is the more usable in that sense, but officially, it is ms-windows only.

This project is sharing an example of a pure GNU-toolchain based solution to writing ASM code for ARM chips. Additionally, it is targetted for Linux as the developer desktop

(using a crosscompiler, not "linux on arm" desktop)

Files of interest

In this directory you should find the following files: (substitute as needed for l4 instead of f4)

Simple blink program

• blink.S - the main code of interest

Button driven blink program

• press.S - the main code of interest

Common definitions

• include/regs_$(CPU).s - Register definitions

Linker requirements

• ld/startup_$(CPU).s - kinda like libc.a, but for ASM
• $(CPU).ld - special defs required by the link stage

How to compile

Make sure you the GNU Arm cross-compiling toolchain. One way is to use the packages provided by the STM folks. (it installs under /opt/st)

Another way, if you have ubuntu, is to simply do

apt install gcc-arm-none-eabi gdb-arm-none-eabi stlink
(or stlink-gui)

How to run (Pure Linux Text Terminal)

First, you need to start up the "st-util" program in the background, or from a separate window.

For convenience, you'll probably want to make a script wrapper, "gdb-debug":

pgrep st-util >/dev/null || {
echo st-util is required;  exit 1
}

if ! test -f "$1" ; then
echo ERROR: need to specify file.elf
exit 1
fi


gdb-multiarch -q -ex 'set architecture armv7' \
-ex 'target extended-remote localhost:4242' \
-ex 'load '$1 -ex 'file '$1

Then in a window you want to debug in, you can then run

gdb-debug blink_STM32F4.elf

and do typical gdb debugging things. You might want to do something like

layout regs
next
next   (note that pressing "return" repeats next)

GDB Multilink annoyance:

If you use the ubuntu packaged gdb instead of the STM tweaked version, you have to "set arch arm" explicitly. So you might want to install the ST.com "Cube" IDE package, even if you dont use their IDE.

and it seems slower.

Original inspiration

At this point, it's pretty much all my code. However, my original experiments were inspired by the following mostly C-based programs

https://github.com/jrsa/stm32f4_blink (C-code based blink app)

https://github.com/libopencm3/libopencm3/ (library used by above)

https://github.com/libopencm3/libopencm3-miniblink (multiple hardware device blink)

https://gist.github.com/BobBurns/bb601d3432650073a8b4 "blinky.s" for Discovery stm32L1

Contributing

I think I have made this somewhat extensible. If for some reason you want to contribute straight ASM versions of the files for your own ARM board, feel free to put up a PR, and I'll be happy to review and consider it for inclusion, giving you credit. Please see the PORTING.md file

To Do

(See TODO file)