Raspberry Pi Zero W Project Part 0 - u-boot building / testing

 1. Raspberry Pi (Pre-4B) Boot Sequence

Currently, loader.bin is not needed.

2. Boot from SD - from power-on to bootcode.bin

• FAT32 formatting - For Linux user's instructions (in fact similar to add a SSD or HDD partition)
• Files needed - bcm2708-rpi-zero-w.dtb, bootcode.bin, start.elf, config.txt  
• modification of bootcode.bin to enable UART is required 
  
• settings in config.txt
• connect UART as following picture

 

3. Toolchain 

GNU Arm Embedded Toolchain - Download

4. u-boot

$ sudo apt-get install flex bison

$ git clone https://github.com/u-boot/u-boot; cd u-boot

$ export PATH=PATH_TO_TOOLCHAIN/gcc-arm-none-eabi-10-2020-q4-major/bin/:$PATH

$ export CROSS_COMPILE=arm-none-eabi-

$ make rpi_0_w_defconfig

$ make -s -j4; cp ./u-boot.bin PATH_TO_SDCARD

5. booting

config.txt:

enable_uart=1
uart_2ndstage=1
kernel=u-boot.bin