* Avoid default PCIe / XHCI probe on CM4 unless required for the
current boot mode (USB_MSD or NVME).
* Leave PCIe RC in reset state when loading start.elf except for
USB-MSD mode.
* Minor update to BRCM SDRAM settings.
* Add USB_MSD_STARTUP_DELAY option (default 0 option).
This adds a configurable delay (in milliseconds) the first time
the USB host controller is initialised before device enumeration.
Normally, this should not be required. However, some HDD enclosures may
require an extended startup delay in order to spinup drives. Without this
the get-capacity command may stall and timeout.
* Use the latest BRCM SDRAM settings.
* FAT12 support for small bootloader ramdisk images.
* Minor file-system performance optimisations.
* Added recovery.bin config.txt option (erase_eeprom=1) to perform
an SPI chip-erase operation instead of programming the bootloader image.
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
