Session requirements

sudo apt-get install gparted
sudo apt-get install qemu-system
sudo apt-get install device-tree-compiler

git clone git://git.denx.de/u-boot.git

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Keywords

1. bootloader.
2. ROM.
3. TPL.
4. Device tree.
5. U-Boot.
6. Labels.
7. SRAM
8. DRAM
9. uImage
10. zImage

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Actions.

0. Booting Sequence.
1. Emulating RASPI3
2. Compile Device tree.
3. Moving from Bootloader to Kernel.
4. configure bootloader to run over SOC.
5. Booting Sequence.
6. Building U-Boot.
7. installing U-Boot.
8. Using U-Boot.

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1. Understanding Booting Sequence.

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🕐 1.1 Important timepoints.

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• t1 ( Hardware Specific ) ▶ Power On self test ( state of hardware = undefined state )

• t1 → t2 ( Running inside ROM code ( Vendor specific ) ).

  • ROM code copy SPL into SRAM.
  • 

• t3: Running SPL ( Secondary program loader ) code (Vendor specific).

  • initializing hardware ( DRAM and DRAM controller ).

• SPL can be found in first partition SD-CARD.

• SPL takes control

• t4: SPL loads bootloader from /boot partition.

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2. Bootloader Mission.

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1. Load Kernel to DRAM.
2. Pass DTB to kernel ( Details Hardware ).
3. Location + size initramfs ( optional ).
4. Gives control to kernel.

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3. Introduction device trees.

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3.1: Device Tree for RASPI3 ( BCM2837 ).

[Binary tree] [Binary Source]

3.2 Operations on Device tree.

1. Device Tree → Binary.

dtc <name>.dts -o <name>.dtb # convert it into binary.

2. Binary → Device tree.

dtc -I dtb -O dts -o output.dts input.dtb

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4. U-BOOT.

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• Support multiple architecture and boards.

Operations

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1. Downloading u-boot.

git clone git://git.denx.de/u-boot.git
cd u-boot

2. Building u-boot for RASPI3.

make rpi_3_defconfig
make CROSS_COMPILE=<toolchain prefix>
#With PATH
make CROSS_COMPILE=`$raspi3`
make CROSS_COMPILE=`${raspi3}`

3. Installing U-boot ( SD-CARD Version )

1. Using gparted tool to create FAT16 partiotion on top of SD-CARD.
2. Installing /boot partiotion.
3. insert SD-CARD into your Hardware.

3. Installing U-boot on top of QEMU Emulator ( TARGET ).

source: https://github.com/ARM-software/u-boot/blob/master/doc/README.qemu-arm

qemu-system-aarch64 \
    -M raspi3b \
    -cpu cortex-a72 \
    -append "rw earlyprintk loglevel=8 console=ttyAMA0,115200" \
    -kernel u-boot.bin \
    -m 1G -smp 4 \
    -serial stdio \
    -usb -device usb-mouse -device usb-kbd \
        -device usb-net,netdev=net0 \
        -netdev user,id=net0,hostfwd=tcp::5555-:22 \

4. Using U-BOOT.

4.1 Convert zImage into uImage ( HOST ).

mkimage -A arm64 -O linux -T kernel -C gzip -a 0x80008000 (load address) \  
-e 0x80008000 (entry point)
-n 'Linux' -d zImage (compressed image) uImage (uBoot Image)

4.2 Loading images from flash into RAM ( inside U-BOOT ).

nand read <RAM address> 280000<nand offset> 400000 <size> # read from nand into RAM.

4.3 Booting Kernel.

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bootm <Kernel address> <address of ramdisk> <address of dtb>

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