Getting Started with the EMAC OE SDK
The EMAC OE SDK is distributed with a set of example projects intended to demonstrate how to use the EMAC OE toolchain and libraries. This page demonstrates the process of compiling an example project and running it on the target machine. Also, it provides a straightforward guide to the essential steps you need to follow to get started with cross compiling a simple program with gcc and running the program on your embedded machine.
Contents
General Information
The EMAC Open Embedded SDK is primarily distributed with our apt repository as a deb file for Ubuntu. EMAC also provides a tarbell you can extract, but recommends the deb file because it's the only version EMAC officially supports.
Each SDK includes the C/C++ header files and libraries compatible with the target hardware. It also includes the C/C++ cross-compiler toolchain components necessary to compile and debug custom application code. The links below will help you get started building and running the example projects on the target hardware.
More information on using Qt Creator with the EMAC SDK is available on the Getting Started With Qt Creator page.
Getting Started with the EMAC OE SDK
Connecting to a Target Board
The next step after establishing a physical connection to the board is logging in. More information on establishing a physical connection to a board is available on the Serial Connections and Network Connections page.
EMAC OE Linux allows login from getty, and SSH (Secure Shell). A getty uses the serial connection or console while SSH utilizes a network connection. For more information visit the System Log In page.
Setting up the Filesystem Read-Write
The filesystems on the remote machines are mounted read-only by default. In order to put your program on the board, you need to make the filesystem read-write.
To set up the root filesytem read-write, enter the following into the terminal:
root@ipac9x25:~# oemntrw Transferring Files
The command line syntax for transferring a file using the SSH protocol is scp file user@host:/directory. SCP or Secure Copy is a way of securely transferring files between a local and remote host. For example, to send the file example.text to the /home directory of a system with the IP address 10.0.6.221, enter the following command:
developer@ldc:~# scp example.text root@10.0.6.221:/home
Alternatively, you can leave of the path after the ':' if you want the file to go directly into the home directory.
developer@ldc:~# scp example.text root@10.0.6.221:
Be aware that this copy operation will fail if the filesystem on the remote machine is mounted read-only, which is the default on most EMAC systems.
Remote Execution
SSH can also be used to execute programs on remote systems without logging in. The syntax for SSH remote execution is ssh user@host "my_command -args file". For example, to run the program hello with the -hi flags on a system with the IP address of 10.0.6.221, enter the following command:
developer@ldc:~# ssh root@10.0.6.221 "/path/to/executable -args"
Basic Compiling
Host Machine Compiling
Create a file called hello.c using a text editor such as vi, vim, nano, or gedit.
Use the following syntax to compile the program called hello.c:
developer@ldc:~# gcc -o hello hello.c If there is no error in your code then the compiler will successfully create an executable file called hello in the current directory.
To verify this, enter the following command:
developer@ldc:~# ls -l hello* -rwxrwxr-x 1 bserrano bserrano 9583 Apr 6 12:45 hello
-rwxr-xr-x 1 bserrano bserrano 129 Apr 6 12:28 hello.c
To run the program, enter the following command:
developer@ldc:~# ./hello Hello EMAC OE!
OR
developer@ldc:~# /path/to/hello Hello EMAC OE!
Target Board Compiling
| NOTE |
| In these examples we are using the Ipac-9x25 board. Your board's processor's architecture will determine which file needs to be sourced. These files come from the EMAC SDK toolchain. |
To compile on the target board, you must source the environment-setup-armv5te-emac-linux-gnueabi file.
developer@ldc:~# source /opt/emac/5.0/environment-setup-armv5te-emac-linux-gnueabi Once you are in the directory with the source file, enter the following command:
developer@ldc:~# $CC -o hello hello.c
| NOTE |
| Once you source the file in your current terminal, you can only use it to cross-compile your program for the target board. You can no longer compile it for your host machine. To compile it to your host machine, simply open a new terminal. |
After sourcing the file, copy the program over to the target board using scp. Enter the following command:
developer@ldc:~# scp hello root@10.0.6.221: root@10.0.6.221's password: hello 100% 9583 9.4KB/s 00:00
After copying the program, you can now execute the program on the target board. Enter the following command:
developer@ldc:~# ssh root@10.0.6.221 ./helloroot@10.0.6.221's password:
Hello EMAC OE!
Linux Filesystem Organization
In order to prevent confusion and promote portability, a standard was created for the organization of the Linux filesystem. To ensure future portability of software created today, promote maintainability of software, and ensure proper utilization of available storage on an embedded machine, this standard should be followed as much as possible. This document covers parts of the standard and gives information about the customizations made to it by EMAC OE to accommodate embedded hardware. A link is provided to the standards document which covers the organization of the Linux filesystem at the end of this document. For more information visit the Linux Filesystem Organization page.
EMAC recommends /usr/local/bin as the location for software you deploy.
/usr/local/bin
| NOTE |
It is important to pay attention to the filesystem structure in order to ensure that your application will work as expected when the filesystem is in production. Reasons for this include:
|
Remote Debugging
Sometimes a program has no technical errors that cause the compile to fail, but fails to meet the developer's expectations when run. This is typically due to algorithm or data structure design errors which can be difficult to find with just visual inspection of the code. Because of this, it can be beneficial to run a debugger targeting the executable process. Debugging is the process of watching what is going on inside of another program while it is running. When a program is compiled with debug symbols included in the binary, it is possible to observe the source code and corresponding assembly code while running the debugger.
When working with embedded systems the binary is usually compiled on a development machine with a different CPU architecture than what is on the target machine. This can be a problem when, as is typically the case, the target machine lacks the system resources to run a debugger. In these cases, it is possible to use the GNU debugger, or GDB, on the development machine to remotely debug the target machine provided it has a program called gdbserver. All EMAC OE builds are packaged with gdbserver to simplify the setup process for developers.
For more information visit the Remote Debugging EMAC OE SDK Projects with gdbserver page.
Examples
Hello World System Log Example
This example will print Hello EMAC OE! to the syslog facility as well as the console. This will allow you to log, debug, and send status messages to the system logger.
To compile and run this program, see the sections above.
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <syslog.h>
int main(int argc, char** argv)
{
char message[] = "Hello EMAC OE!";
openlog("slog", LOG_PID|LOG_CONS, LOG_USER);
syslog(LOG_INFO, "%s", message);
closelog();
printf("%s\n", message);
return 0;
}
This is extremely useful because it allows you to save a record of the output that you might not see first hand.
To verify the program went into the syslog, enter the following command:
developer@ldc:~# tail /var/log/syslogApr 7 14:10:06 ENG-26-LX dhclient: DHCPACK of 10.0.6.237 from 10.0.2.1
Apr 7 14:10:06 ENG-26-LX dhclient: bound to 10.0.6.237 -- renewal in 3306 seconds.
Apr 7 14:17:01 ENG-26-LX CRON[21193]: (root) CMD ( cd / && run-parts --report /etc/cron.hourly)
Apr 7 14:54:41 ENG-26-LX hpcups[21266]: prnt/hpcups/HPCupsFilter.cpp 689: First raster data plane..
Apr 7 14:55:31 hpcups[21266]: last message repeated 3 times
Apr 7 15:05:12 ENG-26-LX dhclient: DHCPREQUEST of 10.0.6.237 on eth0 to 10.0.2.1 port 67
Apr 7 15:05:12 ENG-26-LX dhclient: DHCPACK of 10.0.6.237 from 10.0.2.1
Apr 7 15:05:12 ENG-26-LX dhclient: bound to 10.0.6.237 -- renewal in 3559 seconds.
Apr 7 15:17:01 ENG-26-LX CRON[21302]: (root) CMD ( cd / && run-parts --report /etc/cron.hourly)
Apr 7 15:27:08 ENG-26-LX slog[21375]: Hello EMAC OE!
As you can see on the bottom line, your program output has been recorded and date stamped in the syslog.
