Raspberry Pi Zero W Project Part 0.5 - Documents

Documents

Before starting the project, to collect documents is an important things. 

It is important to study document before and during implementation.

The documents needed in the project are:

1. Raspberry Pi's Official Documents

• Configuration :
• config.txt
• boot.md - default booting address is 0x8000 for RPiZ, it can be specified
  
• UART configuration 
• Raspberry Pi Hardware :
• BCM2835
• Boot modes

2. Broadcom BCM2835 Peripheral specification

3. ARM1176

BCM2825 Address Space

It is important to know the address view of CPU and VPU/GPU. You have to know the difference between physical address and bus address of BCM2835. Otherwise you can't get hardware work correctly.

Why Raspberry Pi Zero WH?

The reasons of selecting RPi ZW as my project platform are:

1. cheap, easy to get one, ARMv6 provides enough features of modern ARM Application processors.
   
2. single core, simple & good for teaching / practice.
3. low power, RPi ZW can be powered by almost any USB slot.
   
4. RPi has a lot of documents / projects / implementations for reference.
   

What's in Next?

In next part, simple assembly programming on RPi Zero W will be introduced. We need to use assembly to implement some important parts of OS and bootloader.

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