USING AM335x NETBOOT FEATURE
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Some boards (like TI AM335x based ones) have quite big on-chip RAM and
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have support for booting via network in ROM. The following describes
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how to setup network booting and then optionally use this support to flash
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NAND and bricked (empty) board with only a network cable.
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I. Building the required images
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1. You have to enable generic SPL configuration options (see
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doc/README.SPL) as well as CONFIG_SPL_NET_SUPPORT,
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CONFIG_ETH_SUPPORT, CONFIG_SPL_LIBGENERIC_SUPPORT and
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CONFIG_SPL_LIBCOMMON_SUPPORT in your board configuration file to build
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SPL with support for booting over the network. Also you have to enable
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the driver for the NIC used and CONFIG_SPL_BOARD_INIT option if your
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board needs some board-specific initialization (TI AM335x EVM does).
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If you want SPL to use some Vendor Class Identifier (VCI) you can set
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one with CONFIG_SPL_NET_VCI_STRING option. am335x_evm configuration
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comes with support for network booting preconfigured.
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2. Define CONFIG_BOOTCOMMAND for your board to load and run debrick
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script after boot:
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#define CONFIG_BOOTCOMMAND \
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"setenv autoload no; " \
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"bootp; " \
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"if tftp 80000000 debrick.scr; then " \
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"source 80000000; " \
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"fi"
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(Or create additional board configuration with such option).
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3. Build U-Boot as usual
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$ make <your_board_name>
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You will need u-boot.img and spl/u-boot.bin images to perform
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network boot. Copy them to u-boot-restore.img and
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u-boot-spl-restore.bin respectively to distinguish this version
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(with automatic restore running) from the main one.
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II. Host configuration.
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1. Setup DHCP server (recommended server is ISC DHCPd).
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- Install DHCP server and setup it to listen on the interface you
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chose to connect to the board (usually configured in
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/etc/default/dhcpd or /etc/default/isc-dhcp-server). Make sure there
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are no other active DHCP servers in the same network segment.
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- Edit your dhcpd.conf and subnet declaration matching the address
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on the interface. Specify the range of assigned addresses and bootfile
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to use. IMPORTANT! Both RBL and SPL use the image filename provided
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in the BOOTP reply but obviously they need different images (RBL needs
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raw SPL image -- u-boot-spl-restore.bin while SPL needs main U-Boot
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image -- u-boot-restore.img). So you have to configure DHCP server to
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provide different image filenames to RBL and SPL (and possibly another
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one to main U-Boot). This can be done by checking Vendor Class
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Identifier (VCI) set by BOOTP client (RBL sets VCI to "DM814x ROM v1.0"
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and you can set VCI used by SPL with CONFIG_SPL_NET_VCI_STRING option,
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see above).
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- If you plan to use TFTP server on another machine you have to set
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server-name option to point to it.
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- Here is sample configuration for ISC DHCPd, assuming the interface
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used to connect to the board is eth0, and it has address 192.168.8.1:
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subnet 192.168.8.0 netmask 255.255.255.0 {
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range dynamic-bootp 192.168.8.100 192.168.8.199;
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if substring (option vendor-class-identifier, 0, 10) = "DM814x ROM" {
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filename "u-boot-spl-restore.bin";
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} elsif substring (option vendor-class-identifier, 0, 17) = "AM335x U-Boot SPL" {
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filename "u-boot-restore.img";
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} else {
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filename "uImage";
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}
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}
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May the ROM bootloader sends another "vendor-class-identifier"
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on the shc board with an AM335X it is:
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"AM335x ROM"
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2. Setup TFTP server.
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Install TFTP server and put image files to it's root directory
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(likely /tftpboot or /var/lib/tftpboot or /srv/tftp). You will need
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u-boot.img and spl/u-boot-spl-bin files from U-Boot build directory.
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III. Reflashing (debricking) the board.
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1. Write debrick script. You will need to write a script that will
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be executed after network boot to perform actual rescue actions. You
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can use usual U-Boot commands from this script: tftp to load additional
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files, nand erase/nand write to erase/write the NAND flash.
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2. Create script image from your script. From U-Boot build directory:
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$ ./tools/mkimage -A arm -O U-Boot -C none -T script -d <your script> debrick.scr
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This will create debrick.scr file with your script inside.
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3. Copy debrick.scr to TFTP root directory. You also need to copy
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there all the files your script tries to load via TFTP. Example script
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loads u-boot.img and MLO. You have to create these files doing regular
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(not restore_flash) build and copy them to tftpboot directory.
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4. Boot the board from the network, U-Boot will load debrick script
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and run it after boot.
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