Sabre Lite

For board details see Sabre Lite

Building for the Sabre Lite

For preset build config, use defconfigs called “sabre_” or “imx6”

Booting on the Sabre Lite

Hardware Requirements

  • 5V/3A power supply
  • RS232 cable (or USB-RS232 adapter)
  • USB OTG cable for Fastboot or Ethernet cable for TFTPboot

Board Setup

The SabreLite can be configured to boot from either USB or SPI flash. USB booting is typically only used when there is a failure in the SPI flash resident bootloader. One may use USB boot to temporarily boot u-boot and reflash the SPI memory.

SPI flash contains a simple boot loader that will can boot from either SPI flash, or from an image starting at block 2 of the SD or μSD card depending on which boot loader has been flashed.

Booting U-Boot from USB

USB booting offers a back door into the system. This method is usually only used to reprogram the SPI flash boot program.

You will first need to acquire and compile the IMX USB loader tool from

git clone git://github.com/boundarydevices/imx_usb_loader.git

NOTE 1: The Element14 Sabrelite platform has its DIP switch mounted incorrectly.

NOTE 2: The connection order is important. You may find that your USB-TTY converter has locked up.

  1. Move the DIP switch nearest the Ethernet port to the OFF position
  2. Move the DIP switch farthest from the Ethernet port to the ON position.
  3. Plug the USB cable into the USB-OTG port located near the HDMI port.
  4. Connect the RS232 port to your computer and open minicom.
  5. Power up the device.

Now you are ready to load your image into memory and execute:

$ lsusb 
.... 
Bus 001 Device 019: ID
15a2:0054 Freescale Semiconductor, Inc.
.... 
$ sudo ./imx_usb image_file

The image file that is used will typically be named u-boot.bin

Booting U-Boot from SPI Flash

To boot from SPI flash:

  1. Move the DIP switch nearest the Ethernet port to the OFF position
  2. Move the DIP switch farthest from the Ethernet port to the OFF position
  3. Connect the RS232 port to your computer and open minicom.
  4. Insert an SD or μSD card depending on which boot loader is resident in SPI flash
  5. Power up the device.

Now you are ready to load your image into memory and execute:

$ lsusb 
....
Bus 001 Device 019: ID 15a2:0054 Freescale Semiconductor, Inc.
.... 
$ sudo ./imx_usb image_file

The image file that is used will typically be named u-boot.bin

Booting U-Boot from SPI Flash

To boot from SPI flash:

  1. Move the DIP switch nearest the Ethernet port to the OFF position
  2. Move the DIP switch farthest from the Ethernet port to the OFF position
  3. Connect the RS232 port to your computer and open minicom.
  4. Insert an SD or μSD card depending on which boot loader is resident in SPI flash
  5. Power up the device.

SD and μSD cards

To boot U-Boot from an SD or μSD card, one must install the appropriate boot loader into SPI flash. The method and boot loader images are provided in the SPI flash programming section. U-Boot must be located at block 2 of the SD or μSD card. This can be achieved with the following command, assuming that the SD or μSD device is /dev/sdb.

dd if=u-boot.bin of=/dev/sdb seek=2 bs=512; sync

U-Boot for the Sabre Lite

Obtaining and Building

There are many versions of U-Boot available for the Sabre Lite. The ones for Android support Fastboot; the mainline ones do not.

We use the one from <git://github.com/boundarydevices/u-boot-2009-08.git> with these patches applied:

Name Purpose
01_android-imx6-uboot-enable_bootelf.patch Enable bootelf command
02_android-imx6-uboot-fastbootfix.patch Fix fastboot to allow the booting of elf and u-boot images
03_android-imx6-uboot-extra_fs_features.patch Add some extra file systems and associated features
04_android-imx6-uboot-update_env.patch Setup default environment. In particular, bootsel4_mmc and bootsel4_net

Prebuilt: u-boot.bin

The prebuilt version is for booting from SPI.

To obtain and build U-Boot, do:

git clone git://github.com/boundarydevices/u-boot-2009-08.git
cd u-boot-2009-08
git checkout origin/boundary-imx_3.0.35_1.1.0 -b boundary-imx_3.0.35_1.1.0
export ARCH=arm
export CROSS_COMPILE=arm-none-eabi-
make mx6q_sabrelite_android_config
make all
ls -l u-boot.bin

Installing U-Boot to SPI Flash

To install U-Boot, put u-boot.bin onto the first partition (either FAT16 or EXT2) of an SD card, boot into U-Boot then do this at the U-Boot prompt:

# Initialise the SD card. Replace 1 with 0 for standard SD
mmc dev 1

# Load the file with name "u-boot.bin" from the 1st partition of the SD card to RAM at address 0x12000000
ext2load mmc 1:1 12000000 u-boot.bin

# Initialise the SPI flash subsystem
sf probe | sf probe 1

# Erase 0x100000 bytes from the SPI flash starting at address 0x00000000 
# This covers both U-Boot and its saved environment.
sf erase 0 0x100000

# Copy ${filesize} bytes from RAM at address 0x12000000 to SPI flash at address 0x00000000
# Note that the filesize variable was set when the file was loaded into RAM
sf write 0x12000000 0 ${filesize}

# Ensure that the boot select switches are set appropriately, then reboot the Sabrelite

Booting seL4 applications

This assumes that the U-Boot version above is installed in SPI flash.

Command Operation
run bootsel4_mmc Scans through the SD card and their partitions looking for an elf file named “sel4-image” in the root directory. This file will be loaded and executed.
run bootsel4_net Performs a DHCP request followed by a TFTPBoot request and attempts to load a file named “sabre/sel4-image”.
run bootsel4_fastboot Simple alias for the fastboot command

Running seL4 test

Checkout the sel4test project using repo as per seL4Test

repo init -u https://github.com/seL4/sel4test-manifest.git
repo sync
make sabre_simulation_debug_xml_defconfig
# The defconfig provides a set build configuration. You can use `make menuconfig` to customize build settings further if necessary.
make
make simulate-sabre

Generated binaries can be found in the images/ directory.