Implementation of s5p4418 bare metal programming (replace 2ndboot)

Refer to instructions ： There are references in this article aven_paul Blogger's S5P4418 Start image analysis , Specific reference http://blog.csdn.net/aven_paul/article/details/46772285

Break the laboratory blogger's “ Lighten up user Led” One article , Specific reference http://weibo.com/p/1001603914482173772682

              S5P4418 It's a four core cortex-A9 Of SOC, Such a powerful processor non operating system cannot give full play to its performance , But for those who want to know more about it and learn to use it better , Bare metal programming allows you to learn more about Power on -> internalRom --> boot mode choose --> Loading & Launch bootloader(BL1 --> BL2 )->...... Detailed process , It can better reflect from SOC To board Until then program Layer by layer connection of , The rigorous design of silk threads . This article uses nanoPi2 Hardware , Only use SD As boot Source , So in order to SD Card as the basis to describe the implementation of bare metal programming .

              adopt S5P4418 Starting the image analysis, we learned that .SD The image in the card is like this ,

Block0	Sd/emmc Card information
Block1	Nsih.bin
Block2	2ndboot.bin
Block63	Nsih.bin
Block64	u-boot.bin

         And some netizens have put their own programs .bin Replace u-boot.bin The way to achieve , see “ Lighten up user Led”http://weibo.com/p/1001603914482173772682, At the same time, the modification is given SD Method of absolute position data in card , That is to use winhex The tool is positioned to the absolute position and modified .

         According to these articles of netizens , I think I should be able to have a preliminary concept of bare metal programming , But it also brings us some doubts , and 2ndboot No source code , For those of us who want to get to the bottom , I always feel that I can't control something , Can we replace our program directly 2ndboot.bin Let's run bare metal ？ I will try it immediately , However, there are still some prerequisites to be done .

        1. find 2ndboot.bin By internalRom Where to carry it to Launch？

         2. If you substitute 2ndboot.bin The way to do it , our bin How big can it be ？

         Take this article , We still have to go to the Official Handbook to find out

         First , We need to look at the system memory map

                          

            Look at this map, We will find that InternalRAM The address is 0xFFFF0000, According to the manual, we know InternalRAM Yes 32KB. good , Is it right? InternalRom Will be able to 2ndboot The content of loading Go to this address to run ？ So we recompile “ Lighten up user LED” Three files in the example of , Just change the link instruction to arm-linux-ld -Ttext=0xffff0000 start.o main.o -o main 了 . We will generate main.bin use winhex Put it in SD Card block2 That is to say 0x400 Location , Insert the card nanoPi2 Of bootSD Card slot , Access to electricity ,very good ,LED Flashing .

            Is it over ？ Maybe .. Well , Maybe not yet

            Now that you can move , We also want to know why

            good , Continue to read the Official Handbook page 3 Chapter System boot. Because we use Internal ROM boot, Use SD Card activation , So switch to 3.4.4 section SDHCBOOT.

                       

       This form tells us , What we can use is 1to32block, Our lights up LED The program is smaller than only 1k Less than , So it won't go beyond the scope , The following sentence is circled in red , describe InternalROM take SD Cary's data comes from Block1 Start load To InternalRAM, our main.bin Yes write SD Card block2 To replace 2ndboot Of , According to the truth, it should be 0xFFFF0000+0x200 It's ours main.bin Location of , Let's modify the compiler connection am-linux-ld -Ttext=0xFFFF0200 start.o main.o -o main. After the complete compilation, the main.bin use winhex write in SD Card 0x400 It's about , Insert the card nanoPi2, Access to electricity ,LED Start blinking , With the connection address 0xffff0000 The effect is the same , Why is that ？

           With questions , I looked at it again start.s, Find jump instructions used internally b start and b main All are relative position jumps . At the same time, I continue to read the official manual about Nsih Description of .

original ,block1 Stored in Nsih It is after the migration exception vector . When the system reset after , adopt exception vector notice , Its jump to Reset_Handler It's about .Reset_Handler Where does it point to ？ We found the official image and extracted it Nsih After the message , Find out , The address is 0xFFFF0200.

in other words , System reset After passage InternalRom Loading , Again exception vector The jump , Jump to our quilt InternalROM Load To InternalRAM To the address in main.bin To run in the .

          At the same time, it means , If you use arm-linux-ld -Ttext=0xffff0000 It's not right , once main.bin Absolute jump in , The program will fly .

To sum up ： To replace your own program 2ndboot To achieve SD Card initiated bare metal programming

                       1.   take main.bin write in SD Card block2 namely 0x400 It's about ;

                       2. If main.bin Less than 15KB, Of the linker at compile time -Ttext=0xFFFF0200

                       3.2. If main.bin Greater than 15kB（512*（32-1））, You need to write it in 0x400 Write a from main.bin The separated from contains load The rest of the code is less than 15KB Part of , Through this 15k The code will main The rest of the is loaded into memory , If main.bin Greater than InternalRAM, You need to write your own external DRAM Code for . This part will not be discussed in this article for the time being .

Reference documents ：http://wiki.friendlyarm.com/wiki/images/3/3d/SEC_Users_Manual_S5P4418_Users_Manual_Preliminary_Ver.0.10.pdf

Reference procedure ：

notes ： Absolute addressing test

take start.s Change to the following code ：

.text
.global _start
_start:
	b st
	.word 0x00000000
	.word 0x00000000
	.word 0x00000000
	.word 0x00000000
	.word 0x00000000
	.word 0x00000000
	.word 0x00000000
st:
	ldr pc, =on_sram
on_sram:
	ldr sp, =0xffff1000
	bl main
halt_loop:
	b halt_loop

Use arm-linux-ld -Ttext=0xFFFF0200  start.o main.o -o main
+ arm-linux-objcopy -I elf32-littlearm -O binary main main.bin

Got main.bin adopt winhex write in SD Card 0x400 inside address , take SD Card insertion nanoPi2, Access to electricity , The little lamp flickered , Thus, the substitution can be verified 2ndboot.bin To use our bare metal code , Be transported to InternalRAM The address in is indeed 0xFFFF0200.