Automatic software update from a TFTP server
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============================================
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Overview
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--------
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This feature allows to automatically store software updates present on a TFTP
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server in NOR Flash. In more detail: a TFTP transfer of a file given in
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environment variable 'updatefile' from server 'serverip' is attempted during
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boot. The update file should be a FIT file, and can contain one or more
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updates. Each update in the update file has an address in NOR Flash where it
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should be placed, updates are also protected with a SHA-1 checksum. If the
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TFTP transfer is successful, the hash of each update is verified, and if the
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verification is positive, the update is stored in Flash.
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The auto-update feature is enabled by the CONFIG_UPDATE_TFTP macro:
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#define CONFIG_UPDATE_TFTP 1
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Note that when enabling auto-update, Flash support must be turned on. Also,
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one must enable FIT and LIBFDT support:
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#define CONFIG_FIT 1
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#define CONFIG_OF_LIBFDT 1
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The auto-update feature uses the following configuration knobs:
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- CONFIG_UPDATE_LOAD_ADDR
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Normally, TFTP transfer of the update file is done to the address specified
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in environment variable 'loadaddr'. If this variable is not present, the
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transfer is made to the address given in CONFIG_UPDATE_LOAD_ADDR (0x100000
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by default).
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- CONFIG_UPDATE_TFTP_CNT_MAX
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CONFIG_UPDATE_TFTP_MSEC_MAX
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These knobs control the timeouts during initial connection to the TFTP
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server. Since a transfer is attempted during each boot, it is undesirable to
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have a long delay when a TFTP server is not present.
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CONFIG_UPDATE_TFTP_MSEC_MAX specifies the number of milliseconds to wait for
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the server to respond to initial connection, and CONFIG_UPDATE_TFTP_CNT_MAX
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gives the number of such connection retries. CONFIG_UPDATE_TFTP_CNT_MAX must
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be non-negative and is 0 by default, CONFIG_UPDATE_TFTP_MSEC_MAX must be
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positive and is 100 by default.
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Since the update file is in FIT format, it is created from an *.its file using
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the mkimage tool. dtc tool with support for binary includes, e.g. in version
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1.2.0 or later, must also be available on the system where the update file is
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to be prepared. Refer to the doc/uImage.FIT/ directory for more details on FIT
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images.
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This mechanism can be also triggered by the command "fitupd".
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If an optional, non-zero address is provided as argument, the TFTP transfer
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is skipped and the image at this address is used.
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The fitupd command is enabled by CONFIG_CMD_FITUPD.
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Example .its files
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------------------
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- doc/uImage.FIT/update_uboot.its
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A simple example that can be used to create an update file for automatically
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replacing U-Boot image on a system.
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Assuming that an U-Boot image u-boot.bin is present in the current working
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directory, and that the address given in the 'load' property in the
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'update_uboot.its' file is where the U-Boot is stored in Flash, the
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following command will create the actual update file 'update_uboot.itb':
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mkimage -f update_uboot.its update_uboot.itb
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Place 'update_uboot.itb' on a TFTP server, for example as
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'/tftpboot/update_uboot.itb', and set the 'updatefile' variable
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appropriately, for example in the U-Boot prompt:
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setenv updatefile /tftpboot/update_uboot.itb
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saveenv
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Now, when the system boots up and the update TFTP server specified in the
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'serverip' environment variable is accessible, the new U-Boot image will be
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automatically stored in Flash.
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NOTE: do make sure that the 'u-boot.bin' image used to create the update
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file is a good, working image. Also make sure that the address in Flash
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where the update will be placed is correct. Making mistake here and
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attempting the auto-update can render the system unusable.
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- doc/uImage.FIT/update3.its
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An example containing three updates. It can be used to update Linux kernel,
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ramdisk and FDT blob stored in Flash. The procedure for preparing the update
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file is similar to the example above.
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TFTP update via DFU
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-------------------
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- It is now possible to update firmware (bootloader, kernel, rootfs, etc.) via
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TFTP by using DFU (Device Firmware Upgrade). More information can be found in
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./doc/README.dfutftp documentation entry.
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