D1 Nezha Development Board understands the basic startup and loading process

Preface

• Familiar with an embedded platform , You need to know how to start the platform , Such as Nand Flash、Nor Flash、SD Card, etc

• Different ways to start , The firmware itself may be stored in different locations , Such as Nand Flash start-up , You need to install all the firmware , Such as boot0、uboot、kernel、rootfs etc. , Download to the specified location first , Or specified storage 【 Partition 】, Block the firmware storage , Used to store firmware with different functions

• image SD card 、NandFlash etc. , Generally, direct code execution is not supported , So it's like Linux Such as system , It's all through bootloader, Start the system in advance , If initialized RAM（SDRAM、DDR SDRAM etc. ）, Copy the code to RAM In the implementation of , therefore Nand Flash、SD The card is mainly used to store code and data ,RAM Used for system startup and operation , Execution of code

• A great deal of CPU chip , Both support multi-level startup , All records on Nezha development board D1 CPU, be based on RISCV64 For my flat head brother C906 The core , It also supports multiple startup modes , Such as SD card 、Nand Flash etc.

• uboot Is common boot Add loader, That is, it has the function of starting and loading , It has the function of firmware upgrade , however CPU Access to electricity , There should be an original startup process , This process is based on CPU Of ROM Starting mode , If you use Nand Flash guide , need boot Mode selection Nand Flash,CPU When powered on, it will take the initiative to Nand Flash A small part of the code in , copy to RAM To carry out , This is it. CPU ROM Of itself boot function , Hardware solidified , The user cannot wipe it out .

• this 【 A little bit of code 】, You need to do a good job in the basic initialization of the system , Such as system clock configuration 、DEBUG Pin configuration 、RAM Initialization etc. , And have 【 Level 2 jump function 】, Jump to uboot etc. bootloader. let me put it another way ,CPU Of itself ROM The firmware , Direct loading is not supported Uboot, But need a bootstrap Type of boot Code , Through this bootstrap start-up uboot, Then continue to guide Linux Isooperating system , Then load the file system , Such a level by level jump and execution

• All records on Nezha development board D1 CPU, It's using ：OpenSBI, As boot0 The way ,CPU After power on , The first run ROM Boot loader in , perform OpenSBI, Then initialize the system , Then go to jump to run uboot Other firmware

• OpenSBI Count as Full ambition D1 CPU The logic program of , May be limited by the boot mode , This OpenSBI The size of the firmware will be limited

Start process

• D1 Nezha development board , Without inserting SD In the case of cards , The on-board... Will be started by default Tina Linux, This startup can be done by viewing 【DEBUG】 Serial port startup information acquisition

• The basic boot mode is ：

• CPU ROM Cut to Nand Flash How to lead

  • OpenSBI v0.6
  • U-Boot 2018.05
  • Linux version 5.4.61
  • BusyBox v1.27.2

• This is the standard Linux The system starts the process

• OpenSBI
  

• U-Boot
  

• Linux kernel
  

• BusyBox rootfs
  

Other thoughts

• If you start RT-Thread Of rt-smart operating system , This is based on Nand Flash What will the startup loading process look like ？

• I think it can be ：

• CPU ROM Cut to Nand Flash How to lead

  • OpenSBI v0.6
  • U-Boot
  • rt-smart
  • userapps

• SD How to start the card , We will continue to study later

Summary

• Preliminary contact D1 Nezha development board , Start to understand the boot mode of the system , Learn how to download firmware

• Firmware download can use ： Quanzhi PhoenixSuit Tools , at present USB The drive is connected , however Generated rt-smart img The mirroring tool does not recognize , So we need to continue our research

• let me put it another way , Need to find a support burning boot0 Tools for , This PhoenixSuit Tools , It is estimated that only Linux That set of firmware burning , By default uboot How to load the boot .

• Later research Nand Flash【 Empty piece 】 burning 、rt-smart Image burning method