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SDP in U-Boot
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SDP stands for serial download protocol. It is the protocol used in NXP's
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i.MX SoCs ROM Serial Downloader and provides means to download a program
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image to the chip over USB and UART serial connection.
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The implementation in U-Boot uses the USB Downloader Gadget (g_dnl) to
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provide a SDP implementation over USB. This allows to download program
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images to the target in SPL/U-Boot using the same protocol/tooling the
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SoC's recovery mechanism is using.
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The SDP protocol over USB is a USB HID class protocol. USB HID class
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protocols allow to access a USB device without OS specific drivers. The
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U-Boot implementation has primarly been tested using the open source
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imx_loader utility (https://github.com/toradex/imx_loader).
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The host side utilities are typically capable to interpret the i.MX
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specific image header (see doc/README.imximage). There are extensions
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for imx_loader's imx_usb utility which allow to interpret the U-Boot
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specific legacy image format (see mkimage(1)). Also the U-Boot side
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support beside the i.MX specific header the U-Boot legacy header.
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Usage
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-----
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This implementation can be started in U-Boot using the sdp command
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(CONFIG_CMD_USB_SDP) or in SPL if Serial Downloader boot mode has been
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detected (CONFIG_SPL_USB_SDP_SUPPORT).
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A typical use case is downloading full U-Boot after SPL has been
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downloaded through the boot ROM's Serial Downloader. Using boot mode
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detection the SPL will run the SDP implementation automatically in
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this case:
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# imx_usb SPL
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Targets Serial Console:
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Trying to boot from USB SDP
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SDP: initialize...
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SDP: handle requests...
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At this point the SPL reenumerated as a new HID device and emulating
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the boot ROM's SDP protocol. The USB VID/PID will depend on standard
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U-Boot configurations CONFIG_G_DNL_(VENDOR|PRODUCT)_NUM. Make sure
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imx_usb is aware of the USB VID/PID for your device by adding a
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configuration entry in imx_usb.conf:
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0x1b67:0x4fff, mx6_usb_sdp_spl.conf
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And the device specific configuration file mx6_usb_sdp_spl.conf:
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mx6_spl_sdp
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hid,uboot_header,1024,0x910000,0x10000000,1G,0x00900000,0x40000
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This allows to download the regular U-Boot with legacy image headers
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(u-boot.img) using a second invocation of imx_usb:
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# imx_usb u-boot.img
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Furthermore, when U-Boot is running the sdp command can be used to
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download and run scripts:
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# imx_usb script.scr
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imx_usb configuration files can be also used to download multiple
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files and of arbitrary types, e.g.
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mx6_usb_sdp_uboot
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hid,1024,0x10000000,1G,0x00907000,0x31000
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full.itb:load 0x12100000
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boot.scr:load 0x12000000,jump 0x12000000
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There is also a batch mode which allows imx_usb to handle multiple
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consecutive reenumerations by adding multiple VID/PID specifications
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in imx_usb.conf:
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0x15a2:0x0061, mx6_usb_rom.conf, 0x1b67:0x4fff, mx6_usb_sdp_spl.conf
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In this mode the file to download (imx_usb job) needs to be specified
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in the configuration files.
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mx6_usb_rom.conf:
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mx6_qsb
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hid,1024,0x910000,0x10000000,1G,0x00900000,0x40000
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SPL:jump header2
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mx6_usb_sdp_spl.conf:
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mx6_spl_sdp
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hid,uboot_header,1024,0x10000000,1G,0x00907000,0x31000
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u-boot.img:jump header2
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With that SPL and U-Boot can be downloaded with a single invocation
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of imx_usb without arguments:
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# imx_usb
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