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Building applications for an OpenWrt Target
Other Notes
Additional Resources
1. 1. OpenWrt
  2. Other C code examples:

Building applications for an OpenWrt Target

There are several ways you can use an OpenWrt Software Development Kit (SDK) or Toolchain to compile your own applications outside of the OpenWrt buildroot :

use prebuilt OpenWrt toolchain to build applications (ie from http://dev.gateworks.com/openwrt/latest/)
use prebuilt OpenWrt SDK to build an OpenWrt package (ie from http://dev.gateworks.com/openwrt/latest/)
use toolchain in your OpenWrt buildroot staging_dir tree (what you may need to do if your running your own firmware with a different lib/kernel config than Gateworks pre-built images)

The point of using the OpenWrt toolchain or SDK is that it can be pre-built and installed on a host that does not have the OpenWrt buildroot.

Note: Custom programming can be achieved through shell scripts on the Gateworks boards (most examples on the Gateworks wiki are shell commands). C code can be used when desired.

OpenWrt Prebuilt Toolchain

If you are using pre-built firmware from http://dev.gateworks.com/openwrt then you can use the pre-built toolchain there to build your own code.

The steps involved:

Download prebuilt toolchain/SDK, the toolchain contains the compiler and standard libraries only.
Uncompress it.
Add it to your path (optional)
Use the toolchain cross compiler to cross compile your code.

Examples:

Example, if you wanted to build a hello-world for OpenWrt 14.08 for the laguna (cns3xxx) platform:

$ wget http://dev.gateworks.com/openwrt/14.08/cns3xxx/OpenWrt-Toolchain-cns3xxx-for-arm_v6k-gcc-4.6-linaro_uClibc-0.9.33.2_eabi.tar.bz2
$ tar xvf OpenWrt-Toolchain-cns3xxx-for-arm_v6k-gcc-4.6-linaro_uClibc-0.9.33.2_eabi.tar.bz2
$ PATH=$PWD/OpenWrt-Toolchain-cns3xxx-for-arm_v6k-gcc-linaro_uClibc-0.9.32_eabi/toolchain-arm_v6k_gcc-linaro_uClibc-0.9.32_eabi/bin:$PATH
$ cat << EOF > hello-world.c
#include <stdio.h>

int main (int argc, char** argv)
{
printf("Hello World\n");
return 0;
}
EOF
$ arm-openwrt-linux-uclibcgnueabi-gcc hello-world.c -o hello-world
$ file hello-world
hello-world: ELF 32-bit LSB executable, ARM, version 1 (SYSV), dynamically linked (uses shared libs), not stripped

Example OpenWrt 16.02 for the Ventana (imx6) platform:

# download toolchain
wget http://dev.gateworks.com/openwrt/16.02/imx6/Gateworks-Toolchain-imx6_gcc-5.2.0_musl-1.1.12_eabi.Linux-x86_64.tar.bz2 
# extract toolchain
tar xvf Gateworks-Toolchain-imx6_gcc-5.2.0_musl-1.1.12_eabi.Linux-x86_64.tar.bz2 
# add toolchain to path
PATH=$PWD/Gateworks-Toolchain-imx6_gcc-5.2.0_musl-1.1.12_eabi.Linux-x86_64/toolchain-arm_cortex-a9+neon_gcc-5.2.0_musl-1.1.12_eabi/bin:$PATH 
# create a simple program
cat << EOF > hello-world.c
#include <stdio.h>

int main (int argc, char** argv)
{
printf("Hello World\n");
return 0;
}
EOF
# compile your program
arm-openwrt-linux-gcc hello-world.c -o hello-world

Note: The prebuilt toolchain may have some issue if the script arm-openwrt-linux-uclibcgnueabi-wrapper.sh is used (with regard to paths having whitespace).

Ventana Notes

If desired, download the Ventana OpenWrt Toolchain/SDK and skip to step 4:

Gateworks-OpenWrt-16.02_20160520-SDK-imx6.tar.bz2 (sha256sum:cb5868daeeafddd5032f0f0380654e5a736530aa1033ae9a8df3b54e77da2ea3)
Gateworks-OpenWrt-16.02_20160520-Toolchain-imx6.tar.bz2 (sha256sum:7098d70fa5ab4d9be91d95261cd2d9552259043520711aa1f893bd8e4b4c9334)

Turn on Toolchain in make menuconfig -> Build the OpenWrt based Toolchain
Compile using make -j8 v=99 in trunk directory
Find compiled toolchain in trunk/bin/imx6/OpenWrt-Toolchain-imx6-for-arm_cortex-a9+neon-gcc-4.6-linaro_uClibc-0.9.33.2_eabi.tar.bz2
Download the toolchain to a different directory on your PC where you will want to do some compiling, such as ~/compiling

Extract the toolchain

ryan@Ryan:~/Documents/toolchain$ tar xvf OpenWrt-Toolchain-imx6-for-arm_cortex-a9+neon-gcc-4.6-linaro_uClibc-0.9.33.2_eabi.tar.bz2 
OpenWrt-Toolchain-imx6-for-arm_cortex-a9+neon-gcc-4.6-linaro_uClibc-0.9.33.2_eabi/
OpenWrt-Toolchain-imx6-for-arm_cortex-a9+neon-gcc-4.6-linaro_uClibc-0.9.33.2_eabi/LICENSE
OpenWrt-Toolchain-imx6-for-arm_cortex-a9+neon-gcc-4.6-linaro_uClibc-0.9.33.2_eabi/toolchain-arm_cortex-a9+neon_gcc-4.6-linaro_uClibc-0.9.33.2_eabi/
OpenWrt-Toolchain-imx6-for-arm_cortex-a9+neon-gcc-4.6-linaro_uClibc-0.9.33.2_eabi/toolchain-arm_cortex-a9+neon_gcc-4.6-linaro_uClibc-0.9.33.2_eabi/lib64
OpenWrt-Toolchain-imx6-for-arm_cortex-a9+neon-gcc-4.6-linaro_uClibc-0.9.33.2_eabi/toolchain-arm_cortex-a9+neon_gcc-4.6-linaro_uClibc-0.9.33.2_eabi/share/
......
.....

Set PATH

ryan@Ryan:~/Documents/toolchain$ PATH=$PWD/OpenWrt-Toolchain-imx6-for-arm_cortex-a9+neon-gcc-4.6-linaro_uClibc-0.9.33.2_eabi/toolchain-arm_cortex-a9+neon_gcc-4.6-linaro_uClibc-0.9.33.2_eabi/bin:$PATH

Create hello-world.c file as shown above,

Compile hello-world.c. Note, when compiling, Gateworks uses hard float, so you may have to specify -mfloat-abi=hard as shown below

ryan@Ryan:~/Documents/toolchain$ arm-openwrt-linux-uclibcgnueabi-gcc -mfloat-abi=hard hello-world.c -o hello-world
arm-openwrt-linux-uclibcgnueabi-gcc.bin: warning: environment variable 'STAGING_DIR' not defined
arm-openwrt-linux-uclibcgnueabi-gcc.bin: warning: environment variable 'STAGING_DIR' not defined
arm-openwrt-linux-uclibcgnueabi-gcc.bin: warning: environment variable 'STAGING_DIR' not defined
/home/ryan/Documents/toolchain/OpenWrt-Toolchain-imx6-for-arm_cortex-a9+neon-gcc-4.6-linaro_uClibc-0.9.33.2_eabi/toolchain-arm_cortex-a9+neon_gcc-4.6-linaro_uClibc-0.9.33.2_eabi/bin/../lib/gcc/arm-openwrt-linux-uclibcgnueabi/4.6.4/../../../../arm-openwrt-linux-uclibcgnueabi/bin/ld: warning: .init_array section has zero size
ryan@Ryan:~/Documents/toolchain$

Verify hello-world has been compiled in current directory

ryan@Ryan:~/Documents/toolchain$ file hello-world
hello-world: ELF 32-bit LSB executable, ARM, version 1 (SYSV), dynamically linked (uses shared libs), not stripped

OpenWrt Prebuilt SDK

If you are using pre-built firmware from http://dev.gateworks.com/openwrt then you can use the pre-built SDK there to build OpenWrt packages. The SDK contains a cross toolchain, libraries, and the Makefile structure to be able to build OpenWrt packages without having an entire buildroot tree. Note that you must also have the OpenWrt Toolchain (see below) in your path. For example to build the OpenWrt nuttcp package for laguna (cns3xxx):

$ wget http://dev.gateworks.com/openwrt/latest/cns3xxx/OpenWrt-SDK-cns3xxx-for-linux-x86_64-gcc-4.6-linaro_uClibc-0.9.33.2.tar.bz2
$ tar xvf OpenWrt-SDK-cns3xxx-for-Linux-i686-gcc-linaro_uClibc-0.9.32.tar.bz2
$ PATH=$PWD/OpenWrt-SDK-imx61-for-linux-x86_64-gcc-4.6-linaro_uClibc-0.9.33.2/staging_dir/toolchain-arm_v7-a_gcc-4.6-linaro_uClibc-0.9.33.2_eabi/bin:$PATH
$ cd OpenWrt-SDK-imx61-for-linux-x86_64-gcc-4.6-linaro_uClibc-0.9.33.2
$ svn export svn://svn.openwrt.org/openwrt/packages/net/nuttcp package/nuttcp
$ make package/nuttcp/compile
$ ls bin/cns3xxx/packages/
nuttcp_6.1.2-2_cns3xxx.ipk  nuttcp-xinetd_6.1.2-2_cns3xxx.ipk

GDB - GNU Debugger

GDB can be used on Gateworks SBC's.

Gateworks has tested GDB in the following way on OpenWrt:

Compile GDB as a package using the make menuconfig option. Be sure it is GDB and not GDB server (example shows GDB server): OpenWrt/Configuration
Install the ipk file on the target board: ipkupload
Compile your program using the toolchain described above but with GDB support. Example is hello-world.
```
arm-openwrt-linux-uclibcgnueabi-gcc -g -mfloat-abi=hard hello-world.c -o hello-world
```
Copy program to target board and be sure it is executable (chmod)
Start gdb on target board (Ventana)

Run the gdb command from the Ventana command prompt:

(gdb) file hello-world 
Load new symbol table from "/hello-world"? (y or n) y
Reading symbols from /hello-world...done.

Then type the run command:

(gdb) run  
Starting program: /hello-world 
warning: Unable to find dynamic linker breakpoint function.
GDB will be unable to debug shared library initializers
and track explicitly loaded dynamic code.
warning: no loadable sections found in added symbol-file /lib/libgcc_s.so.1
warning: no loadable sections found in added symbol-file /lib/libc.so.0
Hello World
[Inferior 1 (process 17906) exited normally]

For more GDB reference please see this page: GDB Documentation and other examples on Google search.

Remote Debugging

A brief example:

From the target start the server using the command to use over TCP on port 2345 the application hello-world
```
root@OpenWrt:/# gdbserver host:2345 hello-world 
```

Example Continues to step 2 below, shown below is the rest of the output:

root@OpenWrt:/# gdbserver host:2345 hello-world 
Process hello-world created; pid = 21696
Listening on port 2345
Remote debugging from host 192.168.1.22
Hello World

Child exited with status 0
GDBserver exiting
root@OpenWrt:/#

From the host start the GDB from the SDK (Ventana example shown)

ryan@Ryan:~/sdk_ventana/OpenWrt-SDK-imx6-for-linux-x86_64-gcc-4.8-linaro_uClibc-0.9.33.2$ ./staging_dir/toolchain-arm_cortex-a9+neon_gcc-4.8-linaro_uClibc-0.9.33.2_eabi/bin/arm-openwrt-linux-uclibcgnueabi-gdb

Attach to target:

(gdb) target remote 192.168.1.1:2345
Remote debugging using 192.168.1.1:2345
0x76ff1e38 in ?? ()
(gdb)

Use the continue command and notice the program run on the target as shown in step 1

(gdb) continue
Continuing.
Cannot access memory at address 0x0
[Inferior 1 (process 23862) exited normally]
(gdb)

Using Toolchain from staging_dir

If you are running firmware from your own OpenWrt build directory you can use the toolchain provided there. The OpenWrt toolchain is placed in staging_dir under a directory name appropriate for your target configuration (toolchain-<arch-info>) and you can use it there to build applications for your target directly without using the buildroot:

laguna - staging_dir/toolchain-arm_v6k_gcc-linaro_uClibc-0.9.32_eabi

Examples:

Cross-compile hello-world.c for Ventana (imx6) using the OpenWrt 16.02, built in the present working directory:

export STAGING_DIR=$PWD/staging_dir
export PATH=$STAGING_DIR/toolchain-arm_cortex-a9+neon_gcc-5.2.0_musl-1.1.12_eabi/bin:$PATH
arm-openwrt-linux-gcc hello-world.c -o hello-world

Cross-compile hello-world.c for Laguna (cns3xxx) using the OpenWrt 14.08, built in the present working directory:

export STAGING_DIR=$PWD/staging_dir
export PATH=$STAGING_DIR/toolchain-arm_v6k_gcc-linaro_uClibc-0.9.32_eabi/bin:$PATH
arm-openwrt-linux-uclibcgnueabi-gcc hello-world.c -o hello-world

Other Notes

uclibc is missing certain things that glibc on your desktop has - There really isn't a clear list of what those items are.

uclibc isn't your only libc option - OpenWrt has support for other popular alternatives to glibc as well (make menuconfig, Advanced configuration options -> Toolchain Options -> C Library implementation).

Current OpenWrt (ie using our trunk BSP) supports uClibc (default) as well as eglibc and musl.
Note that eglibc is extremely popular and I believe Ubuntu has even switched to using it.

If you are missing features in the c++ lib then you can instead/also choose an alternative to uClibc++ via menuconfig 'Global build settings -> Preferred standard C++ library.
- In the toolchain/bin directory, there is a gcc-uc script which sets everything up for uclibc++.
- c++ exceptions have special configuration as noted here http://lists.uclibc.org/pipermail/uclibc-cvs/2012-May/030326.html

Also, if you want to use compiler tools such as 'nm' you need to use the ones from the cross toolchain (ie arm-openwrt-linux-nm)

The STAGING_DIR may need to be set as noted here: http://wiki.openwrt.org/doc/devel/crosscompile

Additional Resources

OpenWrt

OpenWrt is a open source software. There are many OpenWrt resources around the web.
Open WRT Wiki for Cross Compile: http://wiki.openwrt.org/doc/devel/crosscompile
OpenWrt Buildroot : http://wiki.openwrt.org/doc/howto/buildroot.exigence OpenWrt Creating Packages : http://wiki.openwrt.org/doc/devel/packages

Other C code examples:

A userspace daemon has been written by Gateworks, source code is available
http://trac.gateworks.com/wiki/gsc#GSCuserspaceDaemon

Another small sample C program to read through input registers such as temp and voltage on the Gateworks GSC http://trac.gateworks.com/wiki/gsc#SystemTemperatureandVoltageMonitor

Steps:

Write the C code as a .c file such as input.c
Compile the C code with the instructions above
Transfer the resulting executable over to the Gateworks board. One way to do this is through a wget command on the Gateworks board if the executable is hosted on a web server.

Run the executable by chmod 777 if needed, and the type at the command line ./input

#include <stdio.h>
#include <string.h>
/*******************************
*
*  get value  of inputs on Gateworks Boards
*
**********************************/
int getValue(char *file)
{

FILE *fp;

int val=0;

fp = fopen(file,"r");
if ( fp == NULL)
{
        printf("Bad open\n");
        exit(0);
}

while(!feof(fp))
{
if(fscanf(fp,"%d", &val)!=1)
{
        break;
}
else
{

        printf("\nVal=%d\n\n",val);
}
}

fclose(fp);

return val;



}
/*******************************
*
*  get name of inputs on Gateworks Boards
*
**********************************/
const char * getName(char *file)
{

FILE *fp;

char label[100];

fp = fopen(file,"r");
if ( fp == NULL)
{
        printf("Bad open\n");
        exit(0);
}

while(!feof(fp))
{
if(fscanf(fp,"%s", &label)!=1)
{
        break;
}
else
{
        printf("\n\nLabel=%s",label);
}
}

fclose(fp);

}

/*******************************
*
*  dispatch name and value request Gateworks Boards
*
**********************************/
void getNameValuePair(char *file)
{
char filelabel[360];

strcpy(filelabel,file);
strcat (filelabel,"_label");
getName(filelabel);
strcat (file,"_input"); 
getValue(file);
}

/*****************************
*
*   MAIN  read inputs such as voltage
*
*****************************/
int main (int argc, char** argv)
{

        int i=0;
        char str[360];
        char ival[2];
        printf("About to read values...\n");


        for(i=0;i<13;i++)
        {
                strcpy (str," ");
                strcpy (str,"/sys/class/hwmon/hwmon0/device/in");
                sprintf(ival,"%d",i);
                strcat (str,ival);
                getNameValuePair(str);

        }
        return 0;
}

The output once ran on the target Gateworks board looks like:

root@OpenWrt:/# ./input 
About to read values...


Label=vin
Val=23852



Label=3p3
Val=3295



Label=bat
Val=3037



Label=5p0
Val=4983



Label=core
Val=1257



Label=cpu1
Val=16777215



Label=cpu2
Val=16777215



Label=dram
Val=1837



Label=ext_bat
Val=16777215



Label=io1
Val=2505



Label=io2
Val=16777215



Label=pci2
Val=1517



Label=current
Val=775

root@OpenWrt:/#

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