Sonic Alert 2.8 user manual Revision

5.3 Linux Support 25

5.3.9mmcinitrd.u-boot

The mmcinitrd.u-boot userland Makefile target has a lot of parts, but its’ goal is simple

Provide an application developer a means of staying focused on development without the possibility of trashing a flash.

It presumes the existence of an SD card formatted with the VFAT filesys- tem, and a cramfs image on the SD card (in the root as cramfs.img). The mmcinitrd.u-boot file is also typically loaded on the SD card, but that isn’t strictly necessary, as long as it is available and handed to the Linux kernel.

Through a series of steps, it links the /bin, /lib, /usr, /var, /sbin, and /share directories from within cramfs.img, leaving the root of the filesystem read-write (and volatile), with /mmc referring to the root of the SD card.

Furthermore, it presumes the existence of a script or executable named linux init in the root directory of the SD card.

This is done both as an example and as a useful way of nailing down the static pieces of a package (in the cramfs.img file) and allowing read-write access to the filesystem during application development.

The linux init script on the SD card may be modified to start an app directly, without any risk of boot failure.

Look at the file /etc/init.d/rcS for the details of how this is accom- plished.

5.3.10Javascript stuff

Refer to the Boundary Devices’ Javascript Manual for details of the Bound- ary Devices scripting application.

5.3.11Login and SSHD support

By default, the Userland build tool creates a password file /etc/passwd with a root password of BoundaryDevices.

This is only needed when connecting over sshd.

Use the menuconfig make target to change this.

December 28, 2005 Revision 2.8