4700 Cross Compiling

From Technologic Systems Manuals

While you can develop entirely on the board itself, if you prefer to develop from another x86 compatible Linux system we have a cross compiler available. For this board you will want to use this toolchain. To compile your application, you only need to use the version of GCC in the cross toolchain instead of the version supplied with your distribution. The resulting binary will be for ARM.

[user@localhost]$ /opt/arm-2008q3/bin/arm-none-linux-gnueabi-gcc hello.c -o hello
[user@localhost]$ file hello
hello: ELF 32-bit LSB executable, ARM, version 1 (SYSV), dynamically linked (uses shared libs), for GNU/Linux 2.6.14, not stripped

This is one of the simplest examples. If you want to work with a project, you will typically create a makefile. You can read more about makefiles here. Another common requirement is linking to third party libraries provided by Debian on the board. There is no exact set of steps you can take for every project, but the process will be very much the same. Find the headers, and the libraries. Sometimes you have to also copy over their binaries. In this example, I will link to sqlite from Debian (which will also work in the Ubuntu image).

Install the sqlite library and header on the board:

apt-get update && apt-get install -y libsqlite3-0 libsqlite-dev

This will fetch the binaries from the internet and install them. You can list the installed files with dpkg:

dpkg -L libsqlite3-0 libsqlite3-dev

The interesting files from this output will be the .so files, and the .h files. In this case you will need to copy these files to your project directory.

I have a sample example with libsqlite3 below. This is not intended to provide any functionality, but just call functions provided by sqlite.

#include <stdio.h>
#include <stdlib.h>
#include "sqlite3.h"

int main(int argc, char **argv)
{
	sqlite3 *db;
	char *zErrMsg = 0;
	int rc;
	printf("opening test.db\n");
	rc = sqlite3_open("test.db", &db);
	if(rc){
		fprintf(stderr, "Can't open database: %s\n", sqlite3_errmsg(db));
		sqlite3_close(db);
		exit(1);
	}
	if(rc!=SQLITE_OK){
		fprintf(stderr, "SQL error: %s\n", zErrMsg);
	}
	printf("closing test.db\n");
	sqlite3_close(db);
	return 0;
}

To build this with the external libraries I have the makefile below. This will have to be adjusted for your toolchain path. In this example I placed the headers in external/include and the library in external/lib.

CC=/opt/arm-2008q3/bin/arm-none-linux-gnueabi-gcc
CFLAGS=-c -Wall

all: sqlitetest

sqlitetest: sqlitetest.o
        $(CC) sqlitetest.o external/lib/libsqlite3.so.0 -o sqlitetest
sqlitetest.o: sqlitetest.c
        $(CC) $(CFLAGS) sqlitetest.c -Iexternal/include/

clean:  
        rm -rf *o sqlitetest.o sqlitetest

You can then copy this directly to the board and execute it. There are many ways to transfer the compiled binaries to the board. Using a network filesystem such as sshfs or NFS will be the simplest to use if you are frequently updating data, but will require more setup. See your linux distribution's manual for more details. The simplest network method is using ssh/sftp. You can use winscp if from windows, or scp from linux. Make sure you set a password from debian for root or set up a shared key. Otherwise the ssh server will deny connections. From winscp, enter the ip address of the SBC, the root username, and the password you have set or the use of a shared key. This will provide you with an explorer window you can drag files into.

Note: Setting up a password for root is only feasible on the uSD image.

For scp in linux, run:

#replace with your app name and your SBC IP address
scp sqlitetest root@192.168.0.50:/root/

After transferring the file to the board, execute it:

ts:~# ./sqlitetest 
opening test.db
closing test.db