3.1.2.10. U-Boot Falcon Mode
U-Boot’s falcon mode on AM62x bypasses the A-core SPL and U-Boot stage, which allows for booting straight to Linux kernel after OP-TEE and ATF.
Normal boot flow:
R5 SPL -> ATF -> OP-TEE -> Cortex-A SPL -> U-Boot -> Linux
With falcon mode:
R5 SPL -> ATF -> OP-TEE -> Linux
Falcon boot support is added by the ti-falcon yocto override which can be
enabled before building the SDK as follows:
$ echo 'DISTROOVERRIDES:append = ":ti-falcon"' >> conf/local.conf
$ # build the SDK
$ MACHINE=<machine> bitbake -k tisdk-default-image
3.1.2.10.1. Changes made by ti-falcon override:
3.1.2.10.1.1. ATF:
To meet the 2MiB alignment requirement for the Linux kernel’s load address,
the PRELOADED_BL33_BASE (kernel address) is modified to 0x82000000
and K3_HW_CONFIG_BASE (DTB address) is modified from the K3 default to
0x88000000.
3.1.2.10.1.2. TI-SPL:
Falcon mode makes use of a cut down variant of the tispl binary called
tifalcon.bin with the Cortex-A SPL and its corresponding device-tree
removed. This file is deployed to the boot directory inside the root filesystem
so it can be picked by the R5 SPL at boot time.
3.1.2.10.1.3. R5 SPL:
The R5 SPL loads the kernel fitImage and tifalcon.bin file. An
x509 certificate with TIFS keys verifies the fitImage for falcon boot
instead of making use of signature nodes and keys present in the DT. This allows
for faster authentication since TIFS uses the security accelerator for
authentication, which is much faster than doing the same on R5 core.
This support is present alongside the standard R5 defconfig when ti-falcon
is enabled due to U-Boot’s k3_r5_falcon.config fragment. This updates
the R5 memory map at U-Boot SPL stage to the following:
0x80000000 +===============================+ Start of DDR
512KiB | ATF reserved memory space | CONFIG_K3_ATF_LOAD_ADDR
0x80080000 +-------------------------------+
31.5MiB | Unused |
0x82000000 +-------------------------------+ PRELOADED_BL33_BASE in ATF
| | CONFIG_SYS_LOAD_ADDR
57MiB | Kernel + initramfs Image | CONFIG_SPL_LOAD_FIT_ADDRESS
| |
0x85900000 +-------------------------------+
| |
| R5 U-Boot SPL Stack + Heap |
39MiB | (size defined by |
| SPL_STACK_R_MALLOC_SIMPLE_LEN)|
| |
0x88000000 +-------------------------------+ CONFIG_SPL_STACK_R_ADDR
| | K3_HW_CONFIG_BASE in ATF
16MiB | Kernel DTB | CONFIG_SPL_PAYLOAD_ARGS_ADDR
| |
0x89000000 +-------------------------------+
331MiB | Device Manager (DM) Load Addr |
0x9db00000 +-------------------------------+
12MiB | DM Reserved |
0x9e700000 +-------------------------------+
1MiB | Unused |
0x9e800000 +-------------------------------+ BL32_BASE in ATF
24MiB | OPTEE |
0xa0000000 +===============================+ End of DDR (512MiB)
3.1.2.10.1.4. fitImage:
The system produces the resulting fitImage file in the boot directory
of the root filesystem. This file has its constituent binaries pre-signed with
x509 certificates. At boot time, TIFS authenticates this file, which allows for
a lower boot time compared to authenticating on the R5 core.
3.1.2.10.2. Extra Configuration
3.1.2.10.2.1. OSPI boot:
For OSPI boot, the tiboot3.bin file should be flashed to the same
addresses in flash as regular boot flow whereas tifalcon.bin and the
fitImage are read from the root filesystem’s boot directory. The MMC
device is selected by the mmcdev env variable for R5 SPL.
Below U-Boot commands can be used to download tiboot3.bin over tftp
and then flash it to OSPI.
=> sf probe
=> tftp ${loadaddr} tiboot3.bin
=> sf update $loadaddr 0x0 $filesize
3.1.2.10.2.2. eMMC Boot:
In eMMC boot mode, the tiboot3.bin file should be flashed to the
hardware boot partition whereas tifalcon.bin and the fitImage
are read from the root filesystem inside UDA. Use the U-Boot commands below
to set the correct boot partition and write tiboot3.bin to the correct
offset.
=> # Set boot0 as the boot partition
=> mmc partconf 0 1 1 1
=> mmc bootbus 0 2 0 0
=> # Flash tiboot3.bin to boot0
=> mmc dev 0 1
=> fatload mmc 1 ${loadaddr} tiboot3.bin
=> mmc write ${loadaddr} 0x0 0x400
For more information check: How to flash eMMC and boot with eMMC Boot.
3.1.2.10.2.3. Custom fitImage creation:
The following steps show how to create a falcon compatible fitImage:
3.1.2.10.2.4. Non-Yocto Users:
The following steps show how to enable falcon mode from the R5 SPL standalone:
3.1.2.10.3. Boot time comparisons:
Removing A-core SPL and U-Boot from the boot process leads to ~60% reduction in time to kernel. Saving about 1-2 seconds during boot depending on the platform.
Fig. 3.2 Falcon Mode (Left) vs Regular Boot (Right)