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# SPDX-License-Identifier: GPL-2.0+
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#
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# Copyright (C) 2015
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#
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# Lukasz Majewski <l.majewski@majess.pl>
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Device Firmware Upgrade (DFU) - extension to use TFTP
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=====================================================
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Why?
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----
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* Update TFTP (CONFIG_UPDATE_TFTP) only supports writing
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code to NAND memory via TFTP.
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* DFU supports writing data to the variety of mediums (NAND,
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eMMC, SD, partitions, RAM, etc) via USB.
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Combination of both solves their shortcomings!
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Overview
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--------
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This document briefly describes how to use DFU for
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upgrading firmware (e.g. kernel, u-boot, rootfs, etc.)
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via TFTP protocol.
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By using Ethernet (TFTP protocol to be precise) it is
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possible to overcome the major problem of USB based DFU -
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the relatively low transfer speed for large files.
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This was caused by DFU standard, which imposed utilization
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of only EP0 for transfer. By using Ethernet we can circumvent
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this shortcoming.
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Beagle Bone Black rev. C (BBB) powered by TI's am335x CPU has
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been used as a demo board.
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To utilize this feature, one needs to first enable support
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for USB based DFU (CONFIG_DFU_*) and DFU TFTP update
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(CONFIG_DFU_TFTP) described in ./doc/README.update.
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The "dfu" command has been extended to support transfer via TFTP - one
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needs to type for example "dfu tftp 0 mmc 0"
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This feature does not depend on "fitupd" command enabled.
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As of this writing (SHA1:8d77576371381ade83de475bb639949b44941e8c v2015.10-rc2)
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the update.c code is not enabled (CONFIG_UPDATE_TFTP) by any board in the
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contemporary u-boot tree.
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Environment variables
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---------------------
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The "dfu tftp" command can be used in the "preboot" environment variable
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(when it is enabled by defining CONFIG_PREBOOT).
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This is the preferable way of using this command in the early boot stage
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as opposed to legacy update_tftp() function invocation.
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Beagle Bone Black (BBB) setup
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-----------------------------
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1. Setup tftp env variables:
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* select desired eth device - 'ethact' variable ["ethact=cpsw"]
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(use "bdinfo" to check current setting)
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* setup "serverip" and "ipaddr" variables
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* set "loadaddr" as a fixed buffer where incoming data is placed
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["loadaddr=0x81000000"]
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#########
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# BONUS #
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#########
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It is possible to use USB interface to emulate ETH connection by setting
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"ethact=usb_ether". In this way one can have very fast DFU transfer via USB.
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For 33MiB test image the transfer rate was 1MiB/s for ETH over USB and 200KiB/s
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for pure DFU USB transfer.
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2. Setup update_tftp variables:
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* set "updatefile" - the file name to be downloaded via TFTP (stored on
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the HOST at e.g. /srv/tftp)
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3. If required, to update firmware on boot, put the "dfu tftp 0 mmc 0" in the
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"preboot" env variable. Otherwise use this command from u-boot prompt.
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4. Inspect "dfu" specific variables:
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* "dfu_alt_info" - information about available DFU entities
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* "dfu_bufsiz" - variable to set buffer size [in bytes] - when it is not
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possible to set large enough default buffer (8 MiB @ BBB)
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FIT image format for download
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-----------------------------
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To create FIT image for download one should follow the update tftp README file
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(./doc/README.update) with one notable difference:
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The original snippet of ./doc/uImage.FIT/update_uboot.its
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images {
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update@1 {
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description = "U-Boot binary";
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should look like
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images {
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u-boot.bin@1 {
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description = "U-Boot binary";
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where "u-boot.bin" is the DFU entity name to be stored.
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To do
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-----
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* Extend dfu-util command to support TFTP based transfers
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* Upload support (via TFTP)
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