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U-Boot (Universal Boot-loader), developed by Denx Software Engineering, is an open-source bootloader commonly used in embedded systems. It serves as the initial program that loads the operating system, notably the Linux kernel, into DRAM and prepares the system for execution. U-Boot is highly configurable and supports a wide range of architectures and hardware platforms. Moreover, it is licensed as free software under the GNU General Public License, fostering collaborative development and widespread adoption.

Refer to:

U-Boot

The U-Boot Documentation

Contents

Features of U-Boot

Key features and characteristics of U-Boot include:

  1. Versatility: U-Boot is designed to be versatile and can be adapted to various architectures, including ARM, MIPS, x86, and more.

  2. Open Source: U-Boot is released under the GNU General Public License (GPL), providing users with the freedom to view, modify, and distribute the source code.

  3. Boot Sequence Control: U-Boot handles the initialization and configuration of the hardware during the boot process. It allows users to interact with the bootloader through a command-line interface, enabling them to control the boot sequence, load kernel images, and set various parameters.

  4. Support for Various Storage Devices: U-Boot supports loading firmware and kernel images from a variety of storage devices, including NAND and NOR flash memory, SD cards, USB storage, TFTP servers, and more.

  5. Environment Variables: U-Boot allows the configuration of environment variables that store important settings, such as boot parameters and memory addresses.

  6. Network Booting: U-Boot supports network booting, allowing systems to load kernel images and other files over the network using protocols like TFTP or NFS.

  7. Development and Debugging Tools: U-Boot includes tools for debugging and development, such as memory and register inspection, script execution.

Features of U-Boot of SP7350

U-Boot serves as the second-stage bootloader in SP7350 platform. After initializing itself, U-Boot then loads Linux kernel image from external storage devices into DRAM and executes it. As it runs in DRAM, its size is no longer limited by SRAM of SP7350 (only limited by the system's DRAM size), ranging from hundreds of kilobytes to several megabytes.

Apart from its role as a bootloader for loading the Linux kernel, U-Boot supports reading images from external storage devices such as USB flash drives or SD cards and writing images into NOR flash, NAND flash, and eMMC devices in system. Key features of U-Boot for SP7350 are as follows:

  • Support console at UART0 (@ 115,200 bps).

  • Support booting Linux from SPI-NOR flash, SPI-NAND flash, 8-bit NAND flash or eMMC device.

  • Support in-system program (ISP) for SPI-NOR flash, SPI-NAND flash, 8-bit NAND flash or eMMC device.

  • Support read images from USB flash drives or SD cards for in-system program (ISP).

  • Support secure-boot (check hash value of Linux image).

  • Support fastboot function for eMMC device.

  • Support fastboot function for SPI-NAND and 8-bit NAND flashes (only for updating Linux kernel or rootfs partition).

Drivers and features

The source files of U-Boot are conveniently located within the "boot/uboot/" directory under the project's top directory. For the SP7350 platform, a wide array of device drivers is supported. These drivers are within the "drivers" directory. Below is a reference table detailing the drivers along with their corresponding feature descriptions:

Drivers

Folders or files

 Feature descriptions

8-bit NAND

mtd/nand/raw/sp_paranand/

  1. Supports mtd framework.

  2. Supports read and write standard 2k/4k/8k ECC sectors.

  3. Supports read and write 1K60 ECC sectors.

  4. Supports block and chip erase.

Clock

clk/sunplus/

  1. Supports common clock framework (CCF).

  2. Supports clock functions for all devices.

eMMC

mmc/sp_mmc*

  1. Supports MMC framework.

  2. Supports read and write User Data Area.

  3. Supports read and write RPMB partition.

  4. Supports DMA mode.

Ethernet

net/designware.*

  1. Supports 802.3 packets transactions.

  2. Supports 100M and 1000M speeds.

  3. Supports RGMII and RMII interfaces.

I2C

i2c/designware_i2c*

  1. Supports I2C master mode access.

  2. Supports 100kHz and 400kHz speeds.

OTP

soc/sunplus/

  1. Supports write and read OTP.

  2. Supports rotp and wotp commands.

Reset

reset/reset-sunplus.c

  1. Supports reset functions for all devices.

Pinctrl

pinctrl/sunplus/

  1. Supports generic helper bindings.

  2. Supports pin-mux of all devices.

  3. Supports all GPIO pins.

SD card

mmc/sp_sd*

  1. Supports MMC framework.

  2. Supports read and write operations.

  3. Supports DMA mode.

SPI

spi/designware_spi.c

  1. Supports SPI master mode access.

  2. Supports set clock frequency in dts.

  3. Supports mode 0, 1, 2 and 3.

SPI-NAND

mtd/nand/raw/sp_*

  1. Supports mtd framework.

  2. Supports read and write standard 2k ECC sectors.

  3. Supports read and write 1K60 ECC sectors..

  4. Supports block and chip erase.

  5. Supports 4-bit operations.

  6. Supports set clock frequency in dts.

SPI-NOR

mtd/spi/spi-nor-ids.c

spi/sp_spi_nor.c

  1. Supports mtd framework.

  2. Supports read and write operations.

  3. Supports block and chip erase.

  4. Supports set clock frequency in dts.

UART

serial/serial_sunplus.c

  1. Supports U-Boot console at UART0.

  2. Baud rate is set by i-boot.

USB2.0 EHCI

usb/host/ehci-sunplus.c

  1. Supports high-speed read and write operations.

USB2.0 OHCI

usb/host/ohci-sunplus.c

  1. Supports full-speed read and write operations.

USB2.0 UDC

usb/gadget/sp_udc.c

  1. Supports USB devices (gadgets).

USB3.0 DRD

usb/host/xhci-spdwc3.c

usb/gadget/spdwc3_udc.c
phy/phy-sunplus-dwc3.c

  1. Supports super-speed, high-speed and full-speed access.

  2. Supports host and device modes.

  3. Supports USB type C receptacle.

Video

video/sunplus/sp7350/disp/

  1. Supports U-Boot video console.

Other files or folders

Board specific files

Board-specific files for the SP7350 platform can be found in the “board/sunplus/” directory. Below is a breakdown of the folders and their descriptions:

Folders

Descriptions

common/secure_sp7350/

Contains files related to secure boot functionality.

sp7350/

Houses SP7350 platform-specific or hardware-specific files.

Architecture-specific files

Architecture-specific files for the SP7350 platform are situated at “arch/arm/” within the U-Boot directory. Here's a summary of the files and folders:

Files or folders

Descriptions

cpu/armv8/

Contains ARMv8 CPU (ex: Cortex A55) related files.

mach-pentagram/include/mach

Contains platform or hardware-related header files.

mach-pentagram/cpu.c

Encompasses subroutines responsible for CPU reset, memory mapping, DRAM configuration, and more.

Configuration header file

The configuration header file comprises board-specific configuration options, hardware parameters, and initialization settings tailored to the target platform. For the SP7350 platform, the configuration header file is “include/configs/pentagram_common_sp7350_c.h.”

Default configuration files

Default configuration files of U-Boot are stored in the “configs” directory. Specifically for the SP7350 platform, default configuration files are prefixed with “sp7350_”.

Log of U-Boot and explanation

Line 1: Banner (version) of U-Boot.

Line 3: The size of the CPU cache-line is 64 bytes.

Line 4: Model name is ‘Sunplus SP7350’.

Line 5: The DRAM size is 3.8 GiB.

Line 6: PLLA (Audio PLL) is set to 147,456,000 Hz.

Line 7: PLLC (CPU frequency) is set to 1,500,000,000 Hz.

Line 8: PLLL3 (L3 cache frequency) is set to 1,200,000,000 Hz.

Line 9: PLLD (SDRAM PLL) is set to 800,000,000 Hz.

Line 10: PLLH (Peripheral PLL) is set to 2,150,000,000 Hz.

Line 11: PLLN (NPU PLL) is set to 500,000,000 Hz.

Line 12: PLLS (System PLL) is set to 2,000,000,000 Hz.

Line 16: The U-Boot environment variable is successfully loaded.

Line 17-20: The display is successfully probed.

Line 21-23: Standard input, output and error are directed to the serial (UART0)

Line 27-39: Initializing and scanning USB devices.

Line 41: Starting to run the default script command.

Line 42: Boot-device is 0x1F (MX[6..2]), indicating eMMC boot.

Line 43: “[scr] emmc boot” indicates that U-Boot is executing the default 'eMMC boot' script.

Line 45: Loading the header of the Linux kernel image.

Line 47: Loading the Linux kernel image.

Line 48-48: Unzipping the Linux kernel image.

Line 50-58: Preparing to run Linux kernel.

U-Boot 2021.04-g93254255 (Feb 14 2024 - 18:41:47 +0800)

CONFIG_SYS_CACHELINE_SIZE: 64
Model: Sunplus SP7350
DRAM:  3.8 GiB
PLLA            :  147456000 Hz
PLLC            : 1500000000 Hz
PLLL3           : 1200000000 Hz
PLLD            :  800000000 Hz
PLLH            : 2150000000 Hz
PLLN            :  500000000 Hz
PLLS            : 2000000000 Hz
reset: reset@f8800004
SPI:   Manufacturer id = 0x00, Device id = 0x0000 
MMC:   emmc: 0, sd: 1
Loading Environment from MMC... OK
Disp: probe ... 
Disp: init 1920x1080 settings
Disp: lt8912b bridge not found
Disp: probe done 
In:    serial
Out:   serial
Err:   serial
Net:   Could not get PHY for stmmac@f8103000: addr 1
No ethernet found.

starting USB...
Bus usb@f8102100: ehci_sunplus_probe.204, dev_name:usb@f8102100,port_num:0
after write usbruncmd,usbcmd:80b01,retry_times:0
USB EHCI 1.10
Bus usb@f8102080: ohci_sunplus_probe.21, dev_name:usb@f8102080,port_num:1
USB OHCI 1.0
Bus dwc3@f80a1000: Register 2000140 NbrPorts 2
Starting the controller
USB XHCI 1.10
scanning bus usb@f8102100 for devices... 1 USB Device(s) found
scanning bus usb@f8102080 for devices... 1 USB Device(s) found
scanning bus dwc3@f80a1000 for devices... 1 USB Device(s) found
       scanning usb for storage devices... 0 Storage Device(s) found
Hit any key to stop autoboot:  0 
[scr] bootcmd started
fa218008: 0000001f                               ....
[scr] emmc boot

MMC read: dev # 0, block # 8738, count 1 ... 1 blocks read: OK

MMC read: dev # 0, block # 8738, count 19297 ... 19297 blocks read: OK
unzip 10000000 2000000
Uncompressed size: 27285512 = 0x1A05808
booti 2000000 - ef8ec510
## Flattened Device Tree blob at ef8ec510
   Booting using the fdt blob at 0xef8ec510
ehci_usb_remove.214, dev_name:usb@f8102100,port_num:0
ohci_sunplus_remove.28, dev_name:usb@f8102080,port_num:1
   Loading Device Tree to 00000000ef8d9000, end 00000000ef8e987f ... OK

Starting kernel ...
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