1USING AM335x NETBOOT FEATURE 2 3 Some boards (like TI AM335x based ones) have quite big on-chip RAM and 4have support for booting via network in ROM. The following describes 5how to setup network booting and then optionally use this support to flash 6NAND and bricked (empty) board with only a network cable. 7 8 I. Building the required images 9 1. You have to enable generic SPL configuration options (see 10doc/README.SPL) as well as CONFIG_SPL_NET_SUPPORT, 11CONFIG_ETH_SUPPORT, CONFIG_SPL_LIBGENERIC_SUPPORT and 12CONFIG_SPL_LIBCOMMON_SUPPORT in your board configuration file to build 13SPL with support for booting over the network. Also you have to enable 14the driver for the NIC used and CONFIG_SPL_BOARD_INIT option if your 15board needs some board-specific initialization (TI AM335x EVM does). 16If you want SPL to use some Vendor Class Identifier (VCI) you can set 17one with CONFIG_SPL_NET_VCI_STRING option. am335x_evm configuration 18comes with support for network booting preconfigured. 19 2. Define CONFIG_BOOTCOMMAND for your board to load and run debrick 20script after boot: 21#define CONFIG_BOOTCOMMAND \ 22 "setenv autoload no; " \ 23 "bootp; " \ 24 "if tftp 80000000 debrick.scr; then " \ 25 "source 80000000; " \ 26 "fi" 27(Or create additional board configuration with such option). 28 3. Build U-Boot as usual 29 $ make <your_board_name> 30 You will need u-boot.img and spl/u-boot.bin images to perform 31network boot. Copy them to u-boot-restore.img and 32u-boot-spl-restore.bin respectively to distinguish this version 33(with automatic restore running) from the main one. 34 35 II. Host configuration. 36 1. Setup DHCP server (recommended server is ISC DHCPd). 37 - Install DHCP server and setup it to listen on the interface you 38chose to connect to the board (usually configured in 39/etc/default/dhcpd or /etc/default/isc-dhcp-server). Make sure there 40are no other active DHCP servers in the same network segment. 41 - Edit your dhcpd.conf and subnet declaration matching the address 42on the interface. Specify the range of assigned addresses and bootfile 43to use. IMPORTANT! Both RBL and SPL use the image filename provided 44in the BOOTP reply but obviously they need different images (RBL needs 45raw SPL image -- u-boot-spl-restore.bin while SPL needs main U-Boot 46image -- u-boot-restore.img). So you have to configure DHCP server to 47provide different image filenames to RBL and SPL (and possibly another 48one to main U-Boot). This can be done by checking Vendor Class 49Identifier (VCI) set by BOOTP client (RBL sets VCI to "DM814x ROM v1.0" 50and you can set VCI used by SPL with CONFIG_SPL_NET_VCI_STRING option, 51see above). 52 - If you plan to use TFTP server on another machine you have to set 53server-name option to point to it. 54 - Here is sample configuration for ISC DHCPd, assuming the interface 55used to connect to the board is eth0, and it has address 192.168.8.1: 56 57subnet 192.168.8.0 netmask 255.255.255.0 { 58 range dynamic-bootp 192.168.8.100 192.168.8.199; 59 60 if substring (option vendor-class-identifier, 0, 10) = "DM814x ROM" { 61 filename "u-boot-spl-restore.bin"; 62 } elsif substring (option vendor-class-identifier, 0, 17) = "AM335x U-Boot SPL" { 63 filename "u-boot-restore.img"; 64 } else { 65 filename "uImage"; 66 } 67} 68 69 May the ROM bootloader sends another "vendor-class-identifier" 70 on the shc board with an AM335X it is: 71 "AM335x ROM" 72 73 2. Setup TFTP server. 74 Install TFTP server and put image files to it's root directory 75(likely /tftpboot or /var/lib/tftpboot or /srv/tftp). You will need 76u-boot.img and spl/u-boot-spl-bin files from U-Boot build directory. 77 78 III. Reflashing (debricking) the board. 79 1. Write debrick script. You will need to write a script that will 80be executed after network boot to perform actual rescue actions. You 81can use usual U-Boot commands from this script: tftp to load additional 82files, nand erase/nand write to erase/write the NAND flash. 83 84 2. Create script image from your script. From U-Boot build directory: 85 86$ ./tools/mkimage -A arm -O U-Boot -C none -T script -d <your script> debrick.scr 87 88This will create debrick.scr file with your script inside. 89 90 3. Copy debrick.scr to TFTP root directory. You also need to copy 91there all the files your script tries to load via TFTP. Example script 92loads u-boot.img and MLO. You have to create these files doing regular 93(not restore_flash) build and copy them to tftpboot directory. 94 95 4. Boot the board from the network, U-Boot will load debrick script 96and run it after boot. 97