2.3 FIRST STM32 Project - Hello World

As any other programming languages, our first STM32 Project is also "Hello World", without hardware wiring. Using GNU MCU Eclipse to develop STM32 follows the same way to develop any other projects under Eclipse.

2.3.1 Steps to Build Our First Empty Project

A. Create an Empty Project

File->New->C/C++ Project, then click on C++ Managed Build:

Then, click Next.

B. Select STM32F7XX C/C++ Project

In the dialog C++ Project,

under Project type:->Executable, select STM32F7XX C/C++ Project
under Project name:, input Hello World

Then, click Next.

C. Target Processor Settings

In the dialog Target Processor Settings，

under Chip family, select STM32F767xx
under Flash size (kB):, make sure it's 2048
under External clock (Hz):", make sure it's 8000000
under Content:, select Empty (add your own content)
under Use system calls:, select Freestanding (no POSIX system calls)

Then, click Next.

D. Folder settings

Just click Next.

E. Select Configurations

Just click Next.

F. GNU ARM Cross Toolchain

In the dialog GNU ARM Cross Toolchain,

under Toolchain name:, select GNU MCU Eclipse ARM Embedded GCC (arm-none-eabi-gcc)

under Toolchain path:, make sure you put the correct toolchain directory. In our case:

$ ls /opt/GCCToolChains/gnu-mcu-eclipse/arm-none-eabi-gcc/7/bin
arm-none-eabi-addr2line  arm-none-eabi-elfedit    arm-none-eabi-gcc-ranlib  arm-none-eabi-gprof    arm-none-eabi-ranlib
arm-none-eabi-ar         arm-none-eabi-g++        arm-none-eabi-gcov        arm-none-eabi-ld       arm-none-eabi-readelf
arm-none-eabi-as         arm-none-eabi-gcc        arm-none-eabi-gcov-dump   arm-none-eabi-ld.bfd   arm-none-eabi-size
arm-none-eabi-c++        arm-none-eabi-gcc-7.2.1  arm-none-eabi-gcov-tool   arm-none-eabi-nm       arm-none-eabi-strings
arm-none-eabi-c++filt    arm-none-eabi-gcc-ar     arm-none-eabi-gdb         arm-none-eabi-objcopy  arm-none-eabi-strip
arm-none-eabi-cpp        arm-none-eabi-gcc-nm     arm-none-eabi-gdb-py      arm-none-eabi-objdump

Finally, click Finish.

G. Build the Empty Project

Now, let's have a look at the empty project's code:

#include <stdio.h>
#include <stdlib.h>
#include "diag/Trace.h"

// ----------------------------------------------------------------------------
//
// Standalone STM32F7 empty sample (trace via DEBUG).
//
// Trace support is enabled by adding the TRACE macro definition.
// By default the trace messages are forwarded to the DEBUG output,
// but can be rerouted to any device or completely suppressed, by
// changing the definitions required in system/src/diag/trace_impl.c
// (currently OS_USE_TRACE_ITM, OS_USE_TRACE_SEMIHOSTING_DEBUG/_STDOUT).
//

// ----- main() ---------------------------------------------------------------

// Sample pragmas to cope with warnings. Please note the related line at
// the end of this function, used to pop the compiler diagnostics status.
#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wunused-parameter"
#pragma GCC diagnostic ignored "-Wmissing-declarations"
#pragma GCC diagnostic ignored "-Wreturn-type"

int
main(int argc, char* argv[])
{
  // At this stage the system clock should have already been configured
  // at high speed.

  // Infinite loop
  while (1)
    {
       // Add your code here.

    }
}

#pragma GCC diagnostic pop

// ----------------------------------------------------------------------------

Then, we Build Project,

2.3.2 Steps to Build "Hello World"

A. Code Modification

In file main.cpp, add one line printf("Hello World!\n"); under Add your code here. as:

// Add your code here.
printf("Hello World!\n");

B. Build Project - Failure

Why? In the next step, we are going to solve the problem.

C. --specs=nosys.specs

To build the project successfully, we need to set --specs=nosys.specs. But, how to? HelloWorld->Properties->C/C++ Build->Settings->Tool Settings->GNU ARM Cross C++ Linker->Miscellaneous, and tick Do not use syscalls(-specs=nosys.specs).