U-boot falcon mode allows booting directly into Linux from the U-boot secondary program loader (SPL) for devices with limited resources. This provides faster boot times with basic features like environment variables and boot counting available. Board support needs to be added to select SPL and enable falcon mode booting. An example demonstrates booting an iMX6 board 450ms faster using this method by loading the kernel directly instead of mounting partitions.

1. U-boot falcon mode
Lahoudère Fabien

2. 2
U-boot
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Well known bootloader mainly used in embedded
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Handle several architectures
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Support various storage
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Support file systems
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Scriptable

3. 3
U-boot SPL
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SPL (secondary program loader)
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Secondary means the one after boot ROM
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Used to load a first stage for devices with small ressources
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Do minimal hardware initialisation
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Is faster than standard mode to load and start a program (standard u-boot image by
default)
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Falcon mode starts Linux directly

4. 4
U-boot SPL
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How it works
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1. u-boot entry point in arch/arm/lib/crt0.s
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2. Call board_init_f() → do basic board init
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3. Call spl:board_init_r() → start SPL generic code
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4. Optionnaly call spl_board_init for board specific initialisation
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5. Init storage
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6. Optionnaly try to find kernel to boot it (falcon mode)
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7. Start standard u-boot

5. 5
U-boot SPL
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Your board may need some functions:
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Void board_init_f(ulong dummy)
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Void board_boot_order(u32 * spl_boot_list)
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Int spl_start_uboot()
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spl_board_prepare_for_linux()
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spl_board_init()
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Need to add a few configurations for you board
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Select SUPPORT_SPL
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CONFIG_SPL=y

6. 6
U-boot falcon mode
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Is a SPL feature
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Need SPL support for the board
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Allow to start Linux with few initialisation
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Basic features available (env, bootcount, ...)
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Is faster
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Most of uboot features can be ported easily.
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CONFIG_SPL_OS_BOOT=y

7. 7
U-boot falcon mode
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Can boot FIT image
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Can read on partition or raw data
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Support MMC, NAND,NOR, ...
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Need a way to pass kernel arguments (dtb, statically in the
kernel)

8. 8
Add SPL support
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Depend on the board
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Easy if SPL already supported

9. 9
A concrete example
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Adding support for riotboard
ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf- make riotboard_spl_defconfig
ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf- make u-boot-with-spl.imx
sudo ../imx_usb_loader/imx_usb ./u-boot-with-spl.imx

10. 10
A real customer project example
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Imx6 board booting in 450ms instead of 750ms
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Can be better with raw binaries, mounting partition takes time
(100ms)
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Display splash screen after 250ms instead of 500ms

11. 11
Advantages/drawbacks
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Faster
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You can use u-boot
features
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Jump to standard uboot
on demand (GPIO) or on
failure (kernel or dtb not
found)
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Need additional time to
add support to your board.

12. 12
Thank you!