ATSAMA5D27-SOM1-EK1 - Booting from QSPI Flash Memory

Read the Boot Configuration Word

The first step is to read the Boot Configuration Word to learn where it is stored (fuse or backup register) and which one is active. To read the Boot Configuration Word located in the Secure Fuse Controller (SFC), execute the following command on the SAM-BA Host command line:

The result:

SAMA5D2 Series Boot Process

Observe that the Boot Configuration Word bit 22 (DISABLE_BSCR), disable read of Boot Sequence Controller Configuration Register (BSC_CR), is cleared. Therefore, the MPU will read the Boot Sequence Controller Configuration Register (BSC_CR).

You can read the Boot Sequence Controller Configuration Register (BSC_CR) with the following command:

The result:

Observe that the Boot Sequence Controller Configuration Register (BSC_CR) bit 2, validate the data in BUGREG_INDEX field, is cleared. Therefore, no BUREG contains valid boot configuration data.

In summary, the MPU reads the active Boot Configuration Word stored in the SFC. Bit 18, Enable Boot on External Memories, is set/enabled. All remaining bits are in their cleared/default state.

The Boot Configuration Word stored in the SFC can be overridden by the contents of one of four Backup Registers (BUREG). In this step, you will configure the MPU to read the Boot Configuration Word from Backup Register 0 (BUREG0), and in Step 3, you will set the Boot Configuration Word to boot from QSPI Flash memory.

To enable reading of the Boot Configuration Word from Backup Register 0 (BUREG0), perform the following steps:

Set the Boot Configuration Word in BUREG0 to boot from QSPI Flash memory.

The following command will write a Boot Configuration Word to Backup Register 0 (BUREG0) to:

• Boot from external memory, and
• Configure peripheral QSPI1 to IOSET2. This will allow the use of the QSPI Flash memory located on the ATSAMA5D27-SOM1 module (Jumper J13 must be open).

The command also disables reading from QSPI0, SDMMC0, and SDMMC1.

The result:

Upon the next reset, the ATSAMA5D27-SOM1-EK1 evaluation kit will boot from QSPI Flash memory located on the SAMA5D27-SOM1 module. However, the QSPI Flash memory is likely to be empty or hold old code. In the following sections, we show you how to first erase the QSPI Flash memory and then program the second and third-stage bootloaders, at91bootstrap and u-boot-at91.

Erase the QSPI Flash memory on the SAMA5D27-SOM1

Erase the contents of the QSPI Flash memory on the SAMA5D27-SOM1 with the following command:

Change the directory to your working directory containing the at91bootstrap.

Using a default configuration file, configure at91bootstrap with u-boot for QSPI Flash memory:

If you would like to verify the QSPI Flash memory settings or make customization changes:

Observe that Board Type (sama5d27_som1_ek) has been selected.

Highlight Memory selection ---> and press ENTER.

Highlight QSPI Configuration ---> and press ENTER.

Highlight QSPI IOSET Select ---> and press ENTER.

Observe that QSPI IOSET (QSPI1 IOSET 2) ---> has been selected.

You may exit menu config by repeatedly typing "ESC-ESC" until it closes. Do not save any changes.

Build at91bootstrap:

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

$ make
Once the build is complete, the resulting binary files are located in the at91bootstrap/binaries/ directory:

From the SAM-BA Host command line, write at91bootstrap.bin to QSPI Flash memory starting at location 0x0 using the writeboot command:

The result is at91bootstrap.bin is stored in the QSPI Flash memory starting at address 0x0.

Change directory to your working directory containing the u-boot-at91:

Using a default configuration file, configure u-boot-at91 for QSPI Flash memory:

If you would like to verify settings for booting from QSPI Flash memory or make customization changes:

Highlight Boot media ---> and press ENTER.

Observe that [*] Support for booting from QSPI flash ---> has been selected.

You may exit menuconfig by typing "ESC-ESC" repeatedly until it closes. Do not save changes.

Build u-boot-at91:

Once the build is complete, the resulting binary file u-boot.bin is located in the u-boot-at91 directory.

The SAM-BA Host command line, write u-boot.bin to QSPI Flash memory starting at location 0x4000 using the applet -a qspiflash -c write command:

The result is u-boot.bin is stored on the QSPI Flash memory starting at address 0x40000.

Using your favorite text editor, create a text file with the following information. Name the text file u-boot-env.txt.

The bootargs line tells U-Boot:

• The console= device and baud
• The root= location of the root filesystem and permissions
• The rootfstype= that the root filesystem type

The bootcmd= line tells U-Boot to load the sama5d27_som1_ek.itb file (FIT) from the EXT4 formatted partition 2 on the SD memory card (which you will prepare in future sections) to external DDR2 SDRAM starting at address 0x24000000.

Convert the text file u-boot-env.txt into a binary file u-boot-env.bin using the utility program mkenvimage.

From the SAM-BA Host command line, write u-boot-env.bin to QSPI Flash momory at location 0x140000 using the applet -a qspiflash -c write command:

The result is u-boot is stored in the QSPI Flash memory starting at address 0x140000.

Change directory to your working directory containing the linux-at91:

Using default configuration files, configure the Linux kernel:

If you would like to verify settings or make customization changes:

Build linux-at91:

$ make ARCH=arm
Once the build is complete, the resulting binary files are created:

/arch/arm/boot/zImage
/arch/arm/boot/dts/at91-sama5d27_som1_ek.dtb

Git clone the Device Tree Overlay files from the Linux4SAM repository:

Change directory to your working directory containing the dt-overlay-at91:

Open Makefile with your favorite editor and verify the KERNEL_DIR is pointing to your linux-at91 directory:

Or you can set the KERNEL_DIR environment variable:

Build the *.itb image file:

Once the build is complete, the resulting image file sama5d27_som1_ek.itb is located in the dt-overlay-at91 directory. Please remember this because later you will be copying the sama5d27_som1_ek.itb image to the SD memory card.

In the next section, you will prepare an SD memory card.

Download ATSAMA5D27-SOM1-EK1 demonstration image from the Linux4SAM website.

The latest demonstration images for the ATSAMA5D27-SOM1-EK1 are available on the Linux4SAM.org website.

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

• The Yocto Project
• Buildroot
• OpenWRT

Any one of the images can be used for this step. If you are undecided, choose the buildroot_sama5d27_som1_ek-headless file.

Delete the files in the BOOT (FAT32) partition.

Copy the sama5d27_som1_ek.itb file to the ROOTFS/boot directory.

Start a terminal emulation program and configure it to the USB COM port connected to J10.

These two steps set up Console Serial Communications with the target device.

Press the Reset button PB1.

The boot sequence will display in the terminal window. At the end the command line will prompt the user to log in.

Proper operation of the image will be indicated by LED D5 flashing blue which indicates operation of the Linux operating system image.

Proper operation of the on-board J-Link Debugger will be indicated by LED D4 flashing green which indicates operation of the J-Link Debugger.

Congratulations! You have created an embedded Linux system that boots from QSPI Flash memory.