Introduction

Booting an embedded Linux system quickly is crucial for time-critical applications and plays a major role in improving the user experience. This training topic gives some important tips and techniques to achieve fast boot on Microchip microprocessor units (MPUs).

Video: EGT/Linux Fast Boot Demonstration

Linux Boot Process

To begin, let us review the standard boot process on Microchip MPUs running embedded Linux.

A typical embedded Linux boot process involves the following steps:

1. ROM bootloader: This is the ROM boot code contained in the embedded ROM, also known as the first-stage bootloader. It initializes the master clock, configures peripherals and locates the second stage bootloader stored in external Non-Volatile Memory (NVM) and loads it to internal SRAM.
2. at91bootstrap: The second-stage bootloader that initializes clock generator and external DRAM and loads the next stage. The next stage could be a third-stage bootloader (such as U-Boot) or the Linux kernel.
3. U-Boot: Third stage bootloader, which is optional.
4. Linux kernel.
5. Linux target applications.

In this training, you will learn how to launch an Ensemble Graphics Toolkit (EGT) GUI-based application on a Microchip MPU running Linux in under 3 seconds.

Summary of Steps:

• Minimize Boot Time
• Minimize Linux Kernel Load and Startup Time
• Minimize Application Startup Time
• Prepare SD Memory Card
• Fast Boot EGT Application from SD Memory Card

Prerequisites

• Introduction to SAM9X60-EK Evaluation Kit

• Knowledge of the general Boot process is required
  • SAM9X60 Data Sheet (Section 11 – Boot Strategies)

• Attaching the TM5000 WVGA Display to the SAM9X60-EK

• Ensemble Graphics Toolkit
  • EGT – A Free, Open-Source Linux * GUI Toolkit Optimized for Microchip Microprocessors
  • EGT - Preparing the Host PC and Target
  • EGT – First Application with Eclipse IDE

• A working cross-toolchain for ARM-based MPU target is required to complete this topic.
  • You can set one up in the topic: EGT - Preparing the Host PC and Target

Hardware

You will use the SAM9X60-EK Evaluation Kit and a TM5000 High-Performance WVGA Display Module with Max-Touch® Technology.

Refer to "SAM9X60-EK -- Attaching the TM5000 WVGA Display" for instructions on how to assemble the LCD display onto the SAM9X60-EK.

Minimize Boot Time

In this section, you will download, configure, and build the second-stage bootloader, at91bootstrap, for fast booting.

4

Customize the at91bootstrap configuration to minimize boot time.

To customize the default configuration settings, use menuconfig. Menuconfig allows you to view the default configuration and make the required changes.

​

$ make menuconfig

a

Observe that the Board Type (sam9x60ek) ---> has been selected.

b

Highlight Image Loading Strategy and observe that Support loading Linux directly has been selected.

c

Highlight [ ] Debug Support from the main menu and de-select it by pressing <N>.

d

Highlight Hardware Initialization Options ---> and press Enter.

e

De-select Display banner option by pressing <N>. Select <Exit>.

f

Highlight Slow Clock Configuration Options ---> and press Enter.

g

Highlight Select slow clock configuration profile and change the setting to Use Internal RC oscillator as a source of slow clock.

Switching the slow clock source to the internal oscillator will eliminate the settling time required by the external crystal (which is selected by default). This will reduce boot time by almost one second.

h

You may exit menuconfig by repeatedly typing ESC-ESC until it closes. Save changes before exiting.

Minimizing Linux Kernel Load and Startup Time

The Linux kernel load and startup time can be drastically reduced by configuring only the necessary peripherals and subsystems required by the Ensemble Graphics Toolkit (EGT) application. Therefore, from the SAM9X60 default device tree you will disable all the peripherals that are not used by the EGT application. You will also disable them from the kernel configuration. The fewer subsystems and drivers the Kernel must initialize, the faster it will boot. Finally, you will add support for the LCD display.

3

Disable peripherals from the kernel configuration.

Make the following changes to the kernel configurations by running menuconfig.

​

$ cd ~/fastboot/linux-at91/
$ make at91_dt_defconfig ARCH=arm
$ make menuconfig

​

Ensure you set the CROSS_COMPILE=<path_to>/<cross_compiler> and ARCH=arm environment variables.

For example, if your cross-compiler executable is arm-linux-gcc then CROSS_COMPILE=<path_to>/arm-linux-

A second method is you may include these as command variables. For example:

$ make ARCH=arm CROSS_COMPILE=<path_to>/<cross_compiler>

a

Navigate to Networking Support and de-select it by pressing <N>.

b

Highlight Device Drivers ---> and press Enter.

c

Navigate to each of the following unused peripherals and exclude them by pressing <N>.

• Memory Technology device (MTD) support
• Block devices
• SCSI Device support
• SPI support
• PPS support
• Hardware Monitoring support
• Multimedia support
• Sound card support
• USB support
• Staging drivers
• Industrial I/O support

d

Exit menuconfig by repeatedly typing ESC-ESC until it closes. Save changes before exiting.

Minimize Application Startup Time

The Linux kernel loads an init script that loads other services and applications. To minimize boot time, you will replace the standard init script with a minimal script.

The minimal script performs the following:

• Mounts /sysfs, which is needed to control the backlight brightness from within the application.
• Loads the final application, which is a basic automotive dashboard graphical display developed using the Ensemble Graphics Toolkit (EGT).

The application is compiled as a static executable. All the images, logos, and resources are compiled directly into the application and statically linked to it. Therefore, the resources are immediately available and mapped into the application’s address space.

#!/bin/sh

mount -t sysfs none /sys
/usr/bin/egt_dashboard_fastboot
exec /bin/sh

Preparing SD Memory Card Image

In this section, you will download a demonstration image from the Linux4SAM website for the purpose of using the Root File System on the image. You will flash the image to a SD Memory Card and delete the files in the BOOT partition. Finally, you will copy the at91bootstrap.bin, at91-sam9x60ek.dtb and zImage files that you created in the previous section.

1

Download the SAM9X60-EK demonstration image from the Linux4SAM website.

The latest demonstration images for the SAM9X60-EK are available on the Linux4SAM website.

There you will find three sets of images created from one of three Build Systems:

• The Yocto Project
• Buildroot
• OpenWRT

Choose the Buildroot based demo image with graphics support: linux4sam-buildroot-sam9x60ek-graphics-X.Y.img.bz2 where X.Y is the version number (X is year and Y is month of release).

Remove the SD Memory Card from the Linux computer. You have now created a bootable Linux system image on the SD Memory Card.

Note that there are no u-boot images on the SD Memory Card. Recall that you configured and built at91bootstrap to load the Linux kernel directly. This will reduce boot time.

Fast Boot from SD Memory Card

Congratulations! You have reduced the boot time of embedded Linux system with an Ensemble Graphics Toolkit (EGT) application up and running!

Summary

In this training, you changed the standard Linux boot process on the Microchip Microprocessors to reduce the boot time.

• You configured and built at91bootstrap to load the Linux kernel directly.
• You removed all subsystems and kernel drivers that are not used by the final application.
• You used a pre-built RootFS on SD card and replaced the standard init script with a minimal script that just loads the sysfs and EGT application.
• The final application is a EGT Dashboard graphical demo on Microchip PDA5 touchscreen.

The result is a fast boot of the EGT application in less than three seconds on cold reset!