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Subsequently, x-boot loads the images of TF-A (BL31), OP-TEE (BL32), and U-Boot (BL33) from a storage device into DRAM. The CPU (core 0) then switches itself from 32-bit mode to 64-bit by triggering a software reset. It proceeds to awaken other cores (core 1, 2, 3) and transitions them to 64-bit mode. Finally, all cores execute TF-A.
Table of Contents
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Features
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The flow chart below illustrates the process from i-boot's reset vector to the jump to TF-A for all cores
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Source
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Files
The source files for x-boot are located in the "boot/xobot/" directory under the project's top folder. The entry point for x-boot is the label "_start" in the assembly file "arch/arm/sp7350/start.S". Notably, "_start" is situated at an offset of 32 bytes within the x-boot module, with the initial 32-byte space reserved for a header. The "_start" subroutine initializes the C execution environment and subsequently jumps to the C main function, the "xboot_main()" subroutine in the "xboot.c" file. The "xboot.c" file serves as the top-level control file for x-boot, governing the entire flow of operations.
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Files or folders | Descriptions |
adc/ | Contains subroutines for ADC. |
arch/arm/sp7350/ | Houses CPU-relevant codes, including:
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bin/ | Output folder |
common/ | Contains common code, such as verifying images. |
configs/ | Contains defconfig files for boards. |
cpio/ | Contains CPIO codes. |
draminit/ | Contains DRAM-related codes. |
fat/ | Contains codes for FAT file-system operations. |
i2c/ | Contains subroutines for I2C interface. |
include/ | Contains many constant definitions used in x-boot. |
lib/ | Contains images CRC verification codes. |
nand/ | Contains SPI-NAND and 8-bit NAND drivers. |
otp/ | Contains subroutines for accessing OTP. |
romshare/ | Contains the entry table for accessing secure functions in i-boot. |
sdmmc/ | Contains SD card and eMMC drivers. |
tools/ | Contains some utilities used by x-boot. |
usb/ | Contains USB2.0 and USB3.0 drivers. |
warmboot/ | Contains a concise version of x-boot for running during warm-boot. |
Kconfig | Menu config file of x-boot. |
Makefile | Make file of x-boot |
xboot.c | Main C file of x-boot. |
Driver
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Specifications and
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Features
x-boot incorporates a range of device drivers, each offering specific features to facilitate various operations. The following table outlines the detailed specifications and features of these drivers.
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During system boot, i-boot reads boot-related information from the boot switch and the OTP (One-Time Programmable) memory within the chip. This information is then stored in the C structure g_bootinfo. x-boot directly utilizes the data in the g_bootinfo structure to determine the boot mode and process.
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x-boot Log and
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Explanation
Line 1: Banner (version) of x-boot
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