This is a tutorial for using C/C++ compile application in VoCore2.

1. Prepare a USB disk or SD card, at least 256MB, because GCC takes around 110MB. USB disk or SD card must be EXT4 format.

For macOS or Linux, call mkfs.ext4 /dev/disk2 to do this. /dev/disk2 is the USB disk name on my computer, please change to the name on your computer. Or another way, directly format it in VoCore2, need to install e2fsprogs.

opkg update
opkg install e2fsprogs
mkfs.ext4 /dev/sda

NOTE: opkg updaterequires internet, check vocore.io/v2.html, AP+Client mode for wireless connection. Or modify network switch settings, set ethernet port0 to VLAN 2(wan).

This is an example, directly patch /etc/config/network. Another way, you can change virtual network switch in LuCI, Network->Switch.

 config switch_vlan     
         option device 'switch0'
-        option vlan '1'  
+        option vlan '2'    
         option ports '0 6t'

2. Mount SD/USB storage to /overlay

Patch /etc/config/fstab, add target /overlay to make sure once storage is detected, system will auto mount it to /overlay.

config 'global'
        option  anon_swap       '0'
        option  anon_mount      '0'
        option  auto_swap       '1'
        option  auto_mount      '1'
        option  delay_root      '5'
        option  check_fs        '0'

config 'mount'
        option  device  '/dev/sda'
        option  target  '/overlay'
        option  enabled '1'

config 'mount'
        option  device  '/dev/mmcblk0'
        option  target  '/overlay'
        option  enabled '1'

/dev/sda is for USB disk, /dev/mmcblk0 is for SD card.

3. Reboot

Make sure /overlay is valid. You can check by command df.

root@OpenWrt:~# df
Filesystem           1K-blocks      Used Available Use% Mounted on
/dev/root                12800     12800         0 100% /rom
tmpfs                    62492       660     61832   1% /tmp
/dev/mmcblk0          30363504    148636  28649428   1% /overlay
overlayfs:/overlay    30363504    148636  28649428   1% /
tmpfs                      512         0       512   0% /dev

Or another way, directly manually mount /dev/sda or /dev/mmcblk0 to /overlay folder by command mount /dev/sda /overlay.

4. Now we can install GCC

This part is easy, just call

opkg update
opkg install gcc

It will install gcc, ar, binutils,libbfd, objdump, libopcodes packages from openwrt server.

Then we can compile C source code, try gcc yourcode.c -o out. Speed is not very fast, but works.

NOTE: compile better in /tmp folder(it is memory virtual disk) or in /overlay(it is the SD card we inserted). Rest path will store in NOR flash who has very limited write times and very little free space.