U-Boot source from https://github.com/fail0verflow/switch-u-boot.git (at the time, commit a2d885d448eacb72085f262f9b28951384a8e678 was the latest, which was used)
After the clone, the following changes were made before build:
  In arch/arm/dts/tegra210-nintendo-switch.dts: max-frequency = <200000000>; was added to the end of sdhci@700b0000 and sdhci@700b0600 sections (for stability)
  After make nintendo-switch_defconfig, the resulting .config file was edited to have CONFIG_BOOTDELAY=2 , CONFIG_USE_BOOTCOMMAND=y and CONFIG_BOOTCOMMAND="source 80100000"
  Then a make was issued which built the u-boot.elf, included in this binary release

The *.scr.img files were built with the following commands:
  ./tools/mkimage -A arm64 -T script -C none -n "eMMC ums mode" -d ums_emmc.scr ums_emmc.scr.img
  ./tools/mkimage -A arm64 -T script -C none -n "eMMC boot0 ums mode" -d ums_emmc_boot0.scr ums_emmc_boot0.scr.img
  ./tools/mkimage -A arm64 -T script -C none -n "eMMC boot1 ums mode" -d ums_emmc_boot1.scr ums_emmc_boot1.scr.img
  ./tools/mkimage -A arm64 -T script -C none -n "sd ums mode" -d ums_sd.scr ums_sd.scr.img