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Creating a custom MACHINE
The meta-tegra layer includes MACHINE definitions for NVIDIA's Jetson development kits. If you are developing a custom device using one of the Jetson modules with, for example, a custom carrier board, or you just want to modify the default boot-time configuration (pinmux, etc.) for an existing development kit as a separate MACHINE in your own metadata layer, you may need to supply a MACHINE-specific file for your builds.
IMPORTANT: For any custom carrier board/hardware design, make sure you consult the appropriate Platform Adaptation and Bring-Up Guide document available from the NVIDIA Developer Download site to get all the details on how to customize the pinmux configuration and other low-level hardware configuration settings. Failing to provide the correct settings could damage your device.
Boot-time hardware configuration and boot flash programming is particularly complicated for Jetson modules, and varies substantially between models. Consult a recent version of the L4T Driver Package Documentation, particularly the "BSP Customization" and "Bootloader" chapters, for background information. As mentioned above, the Platform Adaptation documentation is also a good reference.
No additional build-time files are necessary for MACHINEs based on the Jetson-TX1 module. All customizations can be done in the device tree and/or U-Boot. You'll need to point your build at your customized kernel and/or U-Boot repository and set variables in the machine .conf file for your custom device.
In the warrior and zeus branches, the only MACHINE-specific build-time file for Jetson-Nano is the SDCard layout file used by recipes-bsp/sdcard-layout/sdcard-layout_1.0.bb. If you modify the partition layout for the SDCard, you'll need to supply a copy of the sdcard-layout.in file that matches the SDCard partitions you define in your customized version of the flash_l4t_t210_spi_sd_p3448.xml file from the L4T BSP.
Starting with the zeus-l4t-r32.3.1 branch, full support for all revisions and SKUs of the Jetson Nano module was added, and the SDcard layout file was eliminated. To modify your partition layout, you need only provide a customized copy of the flash_l4t_t210_spi_sd_p3448.xml (for 0000 SKUs) or flash_l4t_t210_emmc_p3448.xml (for 0002 SKUs) file. Different module revisions (FABs) use different device tree files, so you may need to have multiple device tree source files to account for module variants in your custom device/carrier.
For the Jetson-TX2 family, there are several boot-time configuration files that are machine-specific. Be sure to follow the Platform Adaptation Guide documentation carefully so all of the necessary customizations for the BPMP device tree and the MB1 .cfg files for the pinmux, PMIC, PMC, boot ROM, and other on-module hardware get created properly.
The recipe recipes-bsp/tegra-binaries/tegra-flashvars_<bsp-version>.bb installs a file called flashvars that identifies the boot-time configuration files that need to be processed by the tegra186-flash-helper script for feeding into NVIDIA's flashing tools. You'll need to supply a customized copy of the flashvars file in your BSP layer, and the files listed in that file must be installed into ${datadir}/tegraflash in the build sysroot by another recipe. The recipes-bsp/tegra-binaries/tegra-bootfiles recipe in meta-tegra extracts the files for the Jetson development kits from the L4T BSP package, so look there for more information. The specifics of the configuration files and variables required may vary from version to version of the L4T BSP, so be sure to review any changes when upgrading.
Jetson AGX Xavier systems are similar to Jetson-TX2, but (as of this writing) have only two version-dependent boot-time files - the BPMP device tree and the PMIC configuration. Consult the NVIDIA documentation for customization steps, and see the Jetson-TX2 section above for information on how to integrate your custom files into the build.
Jetson Xavier NX systems are similar to Jetson AGX Xavier, but (as of this writing) have no version-dependent boot-time files. Consult the NVIDIA documentation for customization steps, and see the Jetson-TX2 section above for information on how to integrate your customized files into the build.
For custom hardware, you'll probably need to modify the kernel in at least one of the following ways:
- Custom kernel configuration
- Custom device tree
- Adding patches
Starting with the L4T R32.3.1-based branches, you can use the Yocto Linux tools to apply patches and configuration
changes during the build, although it may be simpler to fork the linux-tegra-4.9 repository to apply patches, and supply your own defconfig file for
the kernel configuration. Having your own fork of the kernel sources should also be easier for creating a custom device tree. (You should also set the KERNEL_DEVICETREE variable in your machine configuration file appropriately.)
If you need to define an alternate MACHINE configuration for an NVIDIA Jetson development kit without altering the boot-time configuration files for hardware initialization, you can have your MACHINE reuse the existing files in meta-tegra. For example, let's say you want to create tegraflash packages for the Jetson-TX2 development kit for both the default cboot->U-boot->Linux boot sequence as well as for booting directly from cboot to Linux, without U-Boot. In your BSP or distro layer, you could add a machine configuration file called, for example, conf/machine/jetson-tx2-cboot.conf that looks like this:
MACHINEOVERRIDES = "jetson-tx2:${MACHINE}"
require conf/machine/jetson-tx2.conf
PACKAGE_EXTRA_ARCHS_append = " jetson-tx2"
PREFERRED_PROVIDER_virtual/bootloader = "cboot-prebuilt"
This would override the bootloader settings in the default jetson-tx2 configuration to use cboot instead of U-Boot, but otherwise reuse all of the MACHINE-specific packages, files, and settings for the jetson-tx2 MACHINE in meta-tegra.