This topic provides info about working with Legato and Yocto.

The Yocto Project is an open source collaboration project that provides templates, tools and methods to help you create custom Linux-based systems for embedded products regardless of the hardware architecture.

Legato is compatible with Yocto 1.7.2

Yocto Linux Directories

Untar the Legato Distribution file to a directory (available at Legato Downloads):

$ cd <some directory>

$ tar xvjf [Legato-Dist-Source file]

These file/directories will be extracted:

downloads - Linux kernel
kernel - Sierra Wireless specific layers
meta-swi - Hardware adaptations
meta-swi-extras - Build scripts and proprietary code

Yocto uses a layered model for its build system. In Legato, device-specific layers are meta-swi-[target] and meta-swi-bin.

Yocto 1.7.2 and poky environment documentation is available at Yocto docs

WP85 and Yocto

The following table lists details about Yocto support for the WP85 module.

Warning: legato-image.wp85.ubi requires fakeroot 1.10.2 for generation.

File Type	Partition	Filename	Def.	Description
bootloader image	mtd0	appsboot.mbn	*	LK (little-kernel), provides fastboot
kernel image	mtd1	boot-yocto-mdm9x15.2k.img	*	kernel (uncompressed) + mdm9x15-image-initramfs
rootfs image	mtd2	mdm9x15-image-minimal-swi-mdm9x15.2k.ubi	*	rootfs as ubi (actual rootfs filesystem is squashfs, read-only)
		mdm9x15-image-minimal-swi-mdm9x15.2k.yaffs2		rootfs as yaffs2 format (not working)
legato image	mtd3	legato-image.wp85.ubi	*	legato as ubi (actual filesystem is squashfs, require fakeroot > 1.10.2 for generation)
		legato-image.wp85.yaffs2		legato as yaffs2 (not working)
packages		boot_wp85.cwe		package with bootloader
		boot-yocto_wp85.cwe		package with bootloader + yocto (= kernel + rootfs)
		boot-yocto-legato_wp85.cwe		package with bootloader + yocto (= kernel + rootfs) + legato
		legato-image.wp85.cwe		package with legato
		yocto_wp85.cwe		package with yocto (= kernel + rootfs)
		yocto-legato_wp85.cwe		package with yocto (= kernel + rootfs) + legato

Pre-built Yocto Image

The prebuilt directory contains a kernel and root file system that can be built using the command below. It's the same as what's flashed on the device, and can be used to return to a known state.

kernel - kernel image
rootfs - smallish root file system ready for basic development.

Instructions on how to flash these images to the device are given in the file README.bsp.

Rebuild Yocto Image

Instructions for rebuilding the image are contained in the file Legato-Yocto1_6/meta-swi-extras/README.build

Running the build script with no arguments will print out the help message. There is also a file called stdbuild.sh to build the images with common options. This can take a long time the first time you run it. Once the build is complete, you'll find new images in the directory:

../build/tmp/deploy/images

Links are created at the end of the build to point to the latest kernel (kernel) and root file system (rootfs)

Warning: You can’t rebuild Yocto images on Ubuntu 13.10.

Linux Flash Yocto

You can flash the Yocto images on Linux;, the device must be in fastboot mode. From the shell prompt on the device run:

root@swi-mdm9x15:~# sys_reboot bootloader

After a few seconds, the device will enumerate as an Android Bootloader Device. You can test this on the development PC with:

dave@devpc$ fastboot devices

MDM9615

Then erase and rewrite the kernel and root filesystem partitions using the fastboot command (the partitions are called kernel and rootfs):

dave@devpc $ fastboot erase kernel
...
dave@devpc $ fastboot erase rootfs
...
dave@devpc $ fastboot flash kernel kernel
...
dave@devpc $ fastboot flash rootfs rootfs
...
dave@devpc $ fastboot reboot
rebooting...
finished. total time: 0.001s

Note: You have to use the micro-USB connection for fastboot

Custom Yocto Image

Because the Legato image is a Yocto-compliant BSP, there are many options for customizing.

Here's the easy way to add some packages to the rootfs:

meta-swi-extras/meta-swi-bin/recipes/images/9615-cdp-sierra-image.inc

For more complex customizations, refer to the Yocto documentation.

Copyright (C) Sierra Wireless Inc. Use of this work is subject to license.