A size of 16MB for the kernel is likely adequate.
-pxe_addr_r:
+pxefile_addr_r:
Mandatory. The location in RAM where extlinux.conf will be loaded to prior
to processing.
device is not attached to USB, and you wish to increase boot speed by
avoiding unnecessary actions.
+boot_net_pci_enum:
+
+ If you want to prevent PCI enumeration by distro boot commands which execute
+ network operations, set the value to something innocuous, e.g. setenv
+ boot_net_pci_enum true. This would be useful if you know your Ethernet
+ device is not attached to PCI, and you wish to increase boot speed by
+ avoiding unnecessary actions.
+
Interactively booting from a specific device at the u-boot prompt
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