Interesting changes since the last default release:-
* Display VC_BUILD_ID strings instead of the SHA256 hash
* Add support for [cm4] and [pi400] config conditionals filters.
* Change network boot to use the same "RXID" Ethernet PHY configuration as the 5.10 kernel
* TFTP - reply to duplicate ACKS
* Skip rendering of HDMI diagnostics display for the first 8 seconds unless an error occurs.
* UDP checksum fixes
* Add support for the BCM2711 XHCI controller - BOOT_ORDER 0x5
* XHCI protocol layer fixes for non-VLI controllers
* Avoid USB MSD timeout of there is only one device
* Implement tryboot for OS upgrade fallback
* Check the update-timestamp before applying an update in SELF-UPDATE mode
* Update recovery.bin to 2021-04-13 release for error pattern fix
on SDRAM failure.
* Reset Ethernet MAC + PHY if final boot mode is not network boot
See: Kernel warning and network failure when attempting to use
the network after bootloader times out. #144
* Improve handling of multiple bootable USB devices and remove USB_MSD_BOOT_MAX_RETRIES
* Resolve: No DHCPACK with DHCP relay agent #58
* Toggle USB root hub port power for 200ms on the first USB MSD boot attempt
See: Bootloader can't boot via USB-HDD after system reboot #151
* Update bootloader handover to support uart_2ndstage - requires a newer
start.elf firmware which will be via rpi-update.
* Assert PCIe fundamental reset if the final bootmode was not USB-MSD
because the OS might not do this before starting XHCI.
* Resolve: Unable to boot from USB MSD - Seagate 5Tb HDD backup drive #139
* Increase USB MSD timeout from 10 to 20 seconds.
* Max retries now default to zero because the default BOOT_ORDER includes
restart (0xf). Therefore, each boot-mode is now tried once before moving
to the next mode. The retries mechanism is largely redudant now that
the loop/restart mode exists.
* If TFTP fails and network boot retries > 0 then wait 5 seconds before
retrying to avoid overloading a misconfigured TFTP server.
* Map undefined boot-modes in BOOT_ORDER to SD (0x1) instead of stopping.
* Add missing pieeprom-2020-05-28
* Resolve: USB boot fails if the GPT contains no basic data or EFI partitions #130
* Resolve: Fix default BOOT_ORDER in mass storage beta #129
* Resolve: Add support for booting from a "superfloppy" disk #120
* Resolve: USB MSD timeout message - incorrect units #131
* Resolve: Recognize efi partition (0xef) as a valid boot #126
* The HDMI diagnostics screen now displays the most significant bytes of the SHA-256 of the config.txt file.
