【System transplantation】 uboot detailed analysis

Uboot usage

    uboot console, countdown
    command: debug, operate some hardware

setenv printenv saveenv 
 nand erase 
 nand write 
 tftp 20008000 zImage
 help: What commands can uboot provide?
 setenv == set == sete == seten

    Environment variables: provide parameters for the command
     serverip: the tftp command provides the address of the tftp server
     ipaddr: the tftp command provides the address of the tftp client (development board)

Two environment variables

    uboot: download the kernel and start the kernel
    bootcmd: what should uboot do automatically after the countdown ends

 set bootcmd tftp 20008000 zImage ; bootm 20008000
 set serverip 192.168.7.2
 set ipaddr 192.168.7.6
 set ethaddr 00:22:23:24:25:ee

   When the countdown ends, uboot will execute the content in bootcmd:
   tftp 20008000 zImage ; bootm 20008000

   Download the zImage file (/tftpboot/) from the tftp server (serverip) to 20008000 in the memory of the development board (ipaddr)

   set bootcmd tftp 20008000 zImage ; bootm 20008000

  bootargs: responsible for telling the kernel where the file system is (uboot passes it to the kernel, which is used by the kernel)

  set bootargs init=/linuxrc console=ttySAC0,115200 root=/dev/nfs nfsroot=192.168.7.2:/opt/filesystem ip=192.168.7.6
  root=xxxx: Where is the root file system directory?
  /dev/nfs: The root file system directory is at the remote end of the network
  
  nfsroot=xxxx: Which file path of which machine is the root file system directory?
  nfsroot=192.168.7.2:/opt/filesystem
  ip=192.168.7.6: When the system logs in, a static ip is assigned.

  If root=/dev/nfs
  root=/dev/nfs + nfsroot=xxxx +ip=xx
  
  If root=/dev/mtdblock2 (will be discussed when the file system is created)
   root=/dev/mtdblock2 + rootfstype=cramfs
  
  console=ttySAC0,115200: During kernel startup, where should the debugging information be output? printk
  init=/linuxrc : Specify the executable code file of the first init process
  /opt/filesystem==> host: /etc/exports
  sudo vim /etc/exports
  /opt/filesystem *(subtree_check,rw,no_root_squash,async)
  /opt/fs100/rootfs *(subtree_check,rw,no_root_squash,async)

Start the kernel: go/bootm

Official uboot

zImage
  : go
  set bootcmd tftp 20008000 zImage ; go 20008000
 
 uImage 
  : bootm(download address, cannot be 20008000)
  set bootcmd tftp 20800000 uImage ; bootm 20800000
 
 selection of download address:
  go==> can be any address
  bootm==> 20008000+zImage size or above==>20800000 
 Comprehensive usage:
  set bootcmd tftp 20800000 zImage ; go 20800000
  set bootcmd tftp 20800000 uImage ; bootm 20800000
uboot1.3.4:
 zImage/uImage ==>bootm
 set bootcmd tftp 20800000 uImage ; bootm 20800000

uboot connection script

    Path: cpu/arm_cortexa8/u-boot.lds

OUTPUT_FORMAT("elf32-littlearm", "elf32-littlearm", "elf32-littlearm")
OUTPUT_ARCH(arm)
ENTRY(_start) // Entry function
SECTIONS
{
        . = 0x00000000; // Current starting position 0x0
        . = ALIGN(4);
        .text(target file) :
        { 
                cpu/arm_cortexa8/start.o (.text) // First file's .text
                *(.text)
        }
        . = ALIGN(4); // Current position four-byte alignment
        .rodata : { *(SORT_BY_ALIGNMENT(SORT_BY_NAME(.rodata*))) }
        . = ALIGN(4);
        .data : { *(.data) }
        . = ALIGN(4);
        .got : { *(.got) }
        __u_boot_cmd_start = .; // Use __u_boot_cmd_start to record the current position. The code will use the global
        .u_boot_cmd: { *(.u_boot_cmd) } // Segment data
        __u_boot_cmd_end = .; // End position
        . = ALIGN(4);
        __bss_start = .;
        .bss: { *(.bss) }
        _end = .;
}

Connection base address:
     -Ttext 0x34800000==>board/samsung/smdkc100/config.mk
     TEXT_BASE = 0x34800000
     1, TEXT_BASE specifies the starting position of the uboot connection
     2, specifies the location of the uboot relocation (can be changed to 0x2ff00000)

Detailed description of uboot configuration

make smdkc100_config
vim Makefile
unconfig:
        @rm -f $(obj)include/config.h $(obj)include/config.mk
                $(obj)board/*/config.tmp $(obj)board/*/*/config.tmp
                $(obj)include/autoconf.mk $(obj)include/autoconf.mk.dep
MKCONFIG := $(SRCTREE)/mkconfig == ./mkconfig Shell script (executable program)

smdkc100_config: unconfig
        @$(MKCONFIG) $(@:_config=) arm arm_cortexa8 smdkc100 samsung s5pc1xx
 ./mkconfig smdkc100 arm arm_cortexa8 smdkc100 samsung s5pc1xx
 Execute a script: 6 parameters are passed (control source code compilation)
 arm: architecture ==> lib_arm
 smdkc100: include/configs/smdkc100.h // Configuration of all macros of the development board
 arm_cortexa8: arm name ==> cpu/arm_cortexa8
 smdkc100 samsung: development board name ==> board/samsung/smdkc100
 s5pc1xx: cpu ==> cpu/arm_cortexa8/s5pc1xx

$(@:_config=): $@:_config= ==>smdkc100_config:_config= // _config is replaced with empty, remove
  $(@:_config=xxx) ===>smdkc100xxx

uboot first stage startup process

1, build exception vector table:
_start: b reset
 ldr pc, _undefined_instruction
 ldr pc, _software_interrupt
 ldr pc, _prefetch_abort
 ldr pc, _data_abort
 ldr pc, _not_used
 ldr pc, _irq
 ldr pc, _fiq

2,
reset:
 /*
  * set the cpu to SVC32 mode, disable F, I
  */
 mrs r0, cpsr
 bic r0, r0, #0x1f
 orr r0, r0, #0xd3
 msr cpsr,r0

 bl cpu_init_crit
   |
   /*
    * Invalidate L1 I/D
    */
   mov r0, #0 @ set up for MCR
   mcr p15, 0, r0, c8, c7, 0 @ invalidate TLBs
   mcr p15, 0, r0, /     * Disable MMU stuff and caches     */    mrc p15, 0, r0, c1, c0, 0
   bic    r0, r0, #0x00002000 @ clear bits 13 (--V-)    bic r0, r0, #0x00000007 @ clear bits 2:0 (-CAM)    orr r0, r0, #0x00000002 @ set bit 1 (--A-) Align    orr r0, r0, #0x00000800 @ set bit 12 (Z---) BTB    mcr p15, 0, r0, c1, c0, 0    bl lowlevel_init //lowlevel_init.S (boardsamsungsmdkc100):lowlevel_init:      |      /* Disable Watchdog */      ldr r0, =S5PC100_WATCHDOG_BASE @0xEA200000      orr r0, r0, #0x0      str r5, [r0]      /* setting SRAM */      ldr r0, =S5PC100_SROMC_BASE      ldr r1, =0x9      str r1, [r0]      /* S5PC100 has 3 groups of interrupt sources */      ldr r0, =S5PC100_VIC0_BASE @0xE4000000      ldr r1, =S5PC100_VIC1_BASE @0xE4000000      ldr r2, =S5PC100_VIC2_BASE @0xE4000000      /* Disable all interrupts (VIC0, VIC1 and VIC2) */      mvn r3, #0x0      str r3, [r0, #0x14] @INTENCLEAR      str r3, [r1, #0x14] @INTENCLEAR      str r3, [r2, #0x14] @INTENCLEAR      /* Set all interrupts as IRQ */      str r5, [r0, #0xc] @INTSELECT      str r5, [r1, #0xc] @INTSELECT      str r5, [r2, #0xc] @INTSELECT      /* Pending Interrupt Clear */      str r5, [r0, #0xf00] @INTADDRESS      str r5, [r1, #0xf00] @INTADDRESS      str r5, [r2, #0xf00] @INTADDRESS      bl uart_asm_init // Just set the gpio function, the baud rate is set in the second stage      #if 1 // The changed part      /* init system clock */      bl system_clock_init // Basically no big problem      bl mem_ctrl_asm_init      //mem_setup.S boardsamsungSmdkc100       // Memory initialization is more complicated, the original manufacturer will provide (1.3.4)      // Ask FAE      // This part of the code has problems running      1, mem_ctrl_asm_init















































     2, mem_setup.S needs to be compiled <=== boardsamsungSmdkc100Makefile
     3, memory initialization code should be in the first 16k (disassembled)
      modify cpu/arm_cotexa8/u-boot.lds

 /* Set up the stack */
stack_setup: ldr
 r0, _TEXT_BASE @ upper 128 KiB: relocated uboot
 sub r0, r0, #CONFIG_SYS_MALLOC_LEN @ malloc area
 sub r0, r0, #CONFIG_SYS_GBL_DATA_SIZE @ bdinfo
#ifdef CONFIG_USE_IRQ
 sub r0, r0, #(CONFIG_STACKSIZE_IRQ + CONFIG_STACKSIZE_FIQ)
#endif
 sub sp, r0, #12 @ leave 3 words for abort-stack
 and sp, sp, #~7 @ 8 byte alinged for (ldr/str)d

Self-copy of uboot code:
 /* nand src offset : 0x0*/
 mov r0, #0x0   
 /* ​​ddr dst addr : 0x2ff00000*/
 ldr r1,=0x2ff00000
 /*size*/
 ldr r2, =0x40000
 bl copy2ddr

ddr address (relocation target address): should be the same as the base address of the uboot link
board/samsung/smdkc100/config.mk
TEXT_BASE=xxxx

Clear bss end 

/* Clear BSS (if any). Is below tx (watch load addr - need space) */
clear_bss:
 ldr r0, _bss_start @ find start of bss segment
 ldr r1, _bss_end @ stop here
 mov r2, #0x00000000 @ clear value
clbss_l:
 str r2, [r0] @ clear BSS location
 cmp r0, r1 @ are we at the end yet
 add r0, r0, #4 @ increment clear index pointer
 bne clbss_l @ keep clearing till at end

Jump to C stage
 ldr pc, _start_armboot @ jump to C code

_start_armboot: .word start_armboot

_start_armboot: .word start_armboot
    //start_armboot's value is determined during compilation: 0x2ff00000+offset==> 0x2ff00980

arm: basically all instructions are position-independent (the instructions can be executed anywhere).
    Some codes are position-dependent: ldr pc, _start_armboot (pc jumps to the target address _start_armboot (0x2ff00980), which is related to a specific location)
    The ldr instruction itself is position-independent, and the entire ldr pc, _start_armboot ==> becomes a position-dependent instruction

Link address: The linker sorts all the instructions. There must be a base address: base address + offset of the instruction.
Run address: The address where the instruction is actually loaded. When running, the address where the instruction is stored.
Physical address: Related to the hardware. The addresses in the data sheet are all physical addresses. The values ​​set by the hardware engineer for the device.
Virtual address: Generally related to MMU.

Ideas:

    1. Support a boot mode nand boot
         a. Initialize the clock and memory
              1. mem_setup.S is compiled
         b. Complete the implementation of self-copy
              nand_ops.c (read operation)
              nand(0x0) --> ddr(TEXT_BASE)
    　        board/samsung/smdkc100/config.mk
         c. The first stage code must all be in the first 16k
              u-boot.lds
         d. Familiar with the first stage boot process code