Create a simple hello-world application

1. Overview

This stage will explain you how to create, build and execute a simple C code application using the freshly installed SDK.

2. Code

• Create your directory that will host your source codes

 mkdir $HOME/STM32MPU_workspace/STM32MP15-Ecosystem-v1.0.0/Developer-Package/sources

• Create a directory for this user space example

 mkdir $HOME/STM32MPU_workspace/STM32MP15-Ecosystem-v1.0.0/Developer-Package/sources/gtk_hello_world_example
 cd $HOME/STM32MPU_workspace/STM32MP15-Ecosystem-v1.0.0/Developer-Package/sources/gtk_hello_world_example

• Create the source code file for this user space example: hello_world_example.c

// SPDX-identifier: GPL-2.0
/*
 * Copyright (C) STMicroelectronics SA 2018
 *
 * Authors: Jean-Christophe Trotin <jean-christophe.trotin@st.com>
 *
 */

#include <stdio.h>
#include <unistd.h>

int main(int argc, char **argv)
{
	int i =11;

	printf("\nUser space example: hello world from STMicroelectronics\n");
	setbuf(stdout,NULL);
	while (i--) {
		printf("%i ", i);
		sleep(1);
	}
	printf("\nUser space example: goodbye from STMicroelectronics\n");

	return(0);
}

3. Build

Three ways to use the OpenSTLinux SDK to cross-compile this user space example are proposed below: (1) command line (2) makefile-based project (3) autotools-based project.

3.1. Command line

This method allows quick cross-compilation of a single-source code file. It applies if the project has only one file.
The cross-development toolchain is associated with the sysroot that contains the header files and libraries needed for generating binaries that run on the target architecture (see SDK for OpenSTLinux distribution#Native and target sysroots).
The sysroot location is specified with the --sysroot option.

The sysroot location must be specified using the --sysroot option. The CC environment variable created by the SDK already includes the --sysroot option that points to the SDK sysroot location.

 echo $CC
arm-openstlinux_weston-linux-gnueabi-gcc -march=armv7ve -marm -mfpu=neon-vfpv4 -mfloat-abi=hard -mcpu=cortex-a7 --sysroot=/local/SDK/2.4+openstlinux-4.14-rocko-mp1-18-07-03/sysroots/cortexa7hf-neon-vfpv4-openstlinux_weston-linux-gnueabi

• Create the directory in which the generated binary is to be stored

 mkdir -p install_artifact install_artifact/usr install_artifact/usr/local install_artifact/usr/local/bin

• Cross-compile the single source code file for the user space example

 $CC hello_world_example.c -o ./install_artifact/usr/local/bin/hello_world_example

3.2. Makefile-based project

For this method, the cross-toolchain environment variables established by running the cross-toolchain environment setup script are subject to general make rules.
For example, see the following environment variables:

 echo $CC
arm-openstlinux_weston-linux-gnueabi-gcc -march=armv7ve -marm -mfpu=neon-vfpv4 -mfloat-abi=hard -mcpu=cortex-a7 --sysroot=/local/SDK/2.4+openstlinux-4.14-rocko-mp1-18-07-03/sysroots/cortexa7hf-neon-vfpv4-openstlinux_weston-linux-gnueabi
 echo $CFLAGS
-O2 -pipe -g -feliminate-unused-debug-types
 echo $LDFLAGS
-Wl,-O1 -Wl,--hash-style=gnu -Wl,--as-needed
 echo $LD
arm-openstlinux_weston-linux-gnueabi-ld --sysroot=/local/SDK/2.4+openstlinux-4.14-rocko-mp1-18-07-03/sysroots/cortexa7hf-neon-vfpv4-openstlinux_weston-linux-gnueabi

• Create the makefile for this user space example: Makefile

Information

All the indentations in a makefile are tabulations

PROG = hello_world_example
SRCS = hello_world_example.c
OBJS = $(SRCS:.c=.o)

CLEANFILES = $(PROG)
INSTALL_DIR = ./install_artifact/usr/local/bin

# Add / change option in CFLAGS if needed
# CFLAGS += <new option>

$(PROG):  $(OBJS)
	$(CC) $(CFLAGS) -o $(PROG) $(OBJS)

.c.o:
	$(CC) $(CFLAGS) -c $< -o $@

all: $(PROG)
 
 
clean:
	rm -f $(CLEANFILES) $(patsubst %.c,%.o, $(SRCS)) *~

install: $(PROG)
	mkdir -p $(INSTALL_DIR)
	install $(PROG) $(INSTALL_DIR)

• Cross-compile the project

 make
 make install

Software development kit (A programming package that enables a programmer to develop applications for a specific platform.)