Skip to content

Latest commit

 

History

History
78 lines (73 loc) · 2.94 KB

c.md

File metadata and controls

78 lines (73 loc) · 2.94 KB
Raw

Working with C

This document contains notes related to building C language programs for ARM cortex microcontrollers.

libopencm3

libopencm3 is an open source firmware library for ARM Cortex-M microcontrollers.

libopencm3 examples

There are examples for various microcontrollers which can be useful references. Just clone that repo and then run:

$ git submodule init
$ git submodule update
$ make

To run an example change to the example directory and run the following command:

$ cd libopencm3-examples/examples/stm32/f0/stm32f0-discovery/miniblink
$ openocd -f board/stm32f0discovery.cfg

The from another terminal we can use telnet to connect and flash the microcontroller:

$ telnet localhost 4444
> reset halt
> flash write_image erase miniblink.elf

This will flash the orange LED on my device.

Building libopencm3

I ran into thie following issue when trying to compile:

$ make
make -C libopencm3 TARGETS=stm32/f1
make[1]: Entering directory '/home/danielbevenius/work/iot/learning-iot/stm32f103c8t6/libopencm3'
  BUILD   lib/stm32/f1
  CC      adc.c
In file included from ../../../include/libopencm3/cm3/common.h:63,
                 from ../../../include/libopencm3/stm32/adc.h:20,
                 from adc.c:94:
/usr/lib/gcc/arm-none-eabi/10.2.0/include/stdint.h:9:16: fatal error: stdint.h: No such file or directory
    9 | # include_next <stdint.h>
      |                ^~~~~~~~~~
compilation terminated.
make[2]: *** [../../Makefile.include:41: adc.o] Error 1
Failure building: lib/stm32/f1: code: 2
make[1]: *** [Makefile:79: lib] Error 1
make[1]: Leaving directory '/home/danielbevenius/work/iot/learning-iot/stm32f103c8t6/libopencm3'
make: *** [Makefile:38: libopencm3/lib/libopencm3_stm32f1.a] Error 2

This issue can be worked around by installing the following library:

$ sudo dnf install -v arm-none-eabi-newlib

libopencm3 source code

If we take a look at the miniblink.c program we used in above we can see that it include two files:

#include <libopencm3/stm32/rcc.h>                                               
#include <libopencm3/stm32/gpio.h>

In the case of the examples libopencm3 is a submodule so the souces will be in libopencm3 in the root directory. Setting up ctags helps with quick navigation. For example. rcc.h can be found in libopencm3-examples/libopencm3/include/libopencm3/stm32/rcc.h. If we take a look in this header we can see that it include headers specific to the version of the microprocessor being used:

#if defined(STM32F0)                                                            
#       include <libopencm3/stm32/f0/rcc.h>

And we a look at that rcc.h header we can see definitions that look familiar from the assembly examples we worked on. Now, this can be useful as a reference if one is unsure of the values taken from the reference manual.