简述代码区的BOOT功能:BOOT0和BOOT1引脚如何控制系统的启动方式?

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重新启动系统的时候按住DEL即可进入BOOT0设置界面，BOOT1启动按F1才能进入系统。 参考技术A 功能：在每个STM32的芯片上都有两个管脚BOOT0和BOOT1，这两个管脚在芯片复位时的电平状态决定了芯片复位后从哪个区域开始执行程序。
方式：
1、Main Flash memory
是STM32内置的Flash，一般我们使用JTAG或者SWD模式下载程序时，就是下载到这个里面，重启后也直接从这启动程序。
2、System memory
从系统存储器启动，这种模式启动的程序功能是由厂家设置的。一般来说，我们选用这种启动模式时，是为了从串口下载程序，因为在厂家提供的BootLoader中，提供了串口下载程序的固件，可以通过这个BootLoader将程序下载到系统的Flash中。

如何使用NASM调用位于后两个扇区的代码？

也许我很蠢，不知道什么，但我认为我做得对。我有两个文件一个boot.asm，第二个code.asm。在boot.asm我只是启用蓝色的视频模式填充屏幕，并尝试加载位于两秒扇区的代码，但当我尝试它没有什么只是发生，无法弄清楚我做错了，也许我读错了或code.asm编码错误或boot.asm编码错误。为什么我不能调用存储在两个第二扇区中的代码来完成它们。

有关更多信息，我将从MBR加载此代码，我希望我的代码调用代码在两个第二扇区，因为我不能将它们全部放在一个扇区中，所以我问这个问题。

boot.asm

;bootloader
  bits 16
  org 0x7c00

;Here i try to load code located at second two sectors
Load_Code:    
    ;---Setup segments
    xor ax, ax                  ; AX=0
    mov ds, ax                  ; DS=ES=0 because we use an org of 0x7c00 - Segment<<4+offset = 0x0000<<4+0x7c00 = 0x07c00
    mov ax, es
    mov ax, ss
    mov sp, 0x7c00              ; SS:SP= 0x0000:0x7c00 stack just below bootloader

  ;---Read 2 sectors
  mov bx, buffer              ; ES: BX must point to the buffer
  mov dh,0                    ; head number
  mov ch,0                    ; track number
  mov cl,2                    ; sector number
  mov al,2                    ; number of sectors to read
  mov ah,2                    ; read function number
  int 13h

;Graphics mode
Set_Video:
  mov ax, 12h        ; Graphics mode (640x480x16)
  int 10h            ; BIOS draw function

  mov ah, 06h        ; Scroll up function
  xor al, al         ; Clear entire screen
  xor cx, cx         ; Upper left corner CH=row, CL=column
  mov dx, 3FFFh      ; fill whole screen
  mov bh, 11h        ; blue background 
  int 10h            ; BIOS draw function
  call buffer

;Endless loop
.endloop:
  hlt
  jmp .endloop


;Fake MBR signature
MBR_Signature:
  times 510 - ($ - $$) db 0
  dw 0xAA55

buffer:

code.asm - 包含此代码的第二个两个扇区 - （这只是示例代码）

mov al, 15         ; color - white
mov ah, 0ch        ; set pixel
mov cx, 0          ; x co-ordinate
mov dx, 0          ; y co-ordinate
int 10h            ; BIOS draw function

mov al, 15         ; color - white
mov ah, 0ch        ; set pixel
mov cx, 1          ; x co-ordinate
mov dx, 1          ; y co-ordinate
int 10h            ; BIOS draw function

mov al, 15         ; color - white
mov ah, 0ch        ; set pixel
mov cx, 2          ; x co-ordinate
mov dx, 2          ; y co-ordinate
int 10h            ; BIOS draw function

mov al, 15         ; color - white
mov ah, 0ch        ; set pixel
mov cx, 3          ; x co-ordinate
mov dx, 3          ; y co-ordinate
int 10h            ; BIOS draw function

mov al, 15         ; color - white
mov ah, 0ch        ; set pixel
mov cx, 4          ; x co-ordinate
mov dx, 4          ; y co-ordinate
int 10h            ; BIOS draw function

mov al, 15         ; color - white
mov ah, 0ch        ; set pixel
mov cx, 5          ; x co-ordinate
mov dx, 5          ; y co-ordinate
int 10h            ; BIOS draw function

mov al, 15         ; color - white
mov ah, 0ch        ; set pixel
mov cx, 6          ; x co-ordinate
mov dx, 6          ; y co-ordinate
int 10h            ; BIOS draw function

mov al, 15         ; color - white
mov ah, 0ch        ; set pixel
mov cx, 7          ; x co-ordinate
mov dx, 7          ; y co-ordinate
int 10h            ; BIOS draw function

mov al, 15         ; color - white
mov ah, 0ch        ; set pixel
mov cx, 8          ; x co-ordinate
mov dx, 8          ; y co-ordinate
int 10h            ; BIOS draw function

mov al, 15         ; color - white
mov ah, 0ch        ; set pixel
mov cx, 9          ; x co-ordinate
mov dx, 9          ; y co-ordinate
int 10h            ; BIOS draw function

mov al, 15         ; color - white
mov ah, 0ch        ; set pixel
mov cx, 10         ; x co-ordinate
mov dx, 10         ; y co-ordinate
int 10h            ; BIOS draw function

mov al, 15         ; color - white
mov ah, 0ch        ; set pixel
mov cx, 11         ; x co-ordinate
mov dx, 11         ; y co-ordinate
int 10h            ; BIOS draw function

mov al, 15         ; color - white
mov ah, 0ch        ; set pixel
mov cx, 12         ; x co-ordinate
mov dx, 12         ; y co-ordinate
int 10h            ; BIOS draw function

mov al, 15         ; color - white
mov ah, 0ch        ; set pixel
mov cx, 13         ; x co-ordinate
mov dx, 13         ; y co-ordinate
int 10h            ; BIOS draw function

mov al, 15         ; color - white
mov ah, 0ch        ; set pixel
mov cx, 14         ; x co-ordinate
mov dx, 14         ; y co-ordinate
int 10h            ; BIOS draw function

mov al, 15         ; color - white
mov ah, 0ch        ; set pixel
mov cx, 15         ; x co-ordinate
mov dx, 15         ; y co-ordinate
int 10h            ; BIOS draw function

mov al, 15         ; color - white
mov ah, 0ch        ; set pixel
mov cx, 16         ; x co-ordinate
mov dx, 16         ; y co-ordinate
int 10h            ; BIOS draw function

mov al, 15         ; color - white
mov ah, 0ch        ; set pixel
mov cx, 17         ; x co-ordinate
mov dx, 17         ; y co-ordinate
int 10h            ; BIOS draw function

mov al, 15         ; color - white
mov ah, 0ch        ; set pixel
mov cx, 18         ; x co-ordinate
mov dx, 18         ; y co-ordinate
int 10h            ; BIOS draw function

mov al, 15         ; color - white
mov ah, 0ch        ; set pixel
mov cx, 19         ; x co-ordinate
mov dx, 19         ; y co-ordinate
int 10h            ; BIOS draw function

mov al, 15         ; color - white
mov ah, 0ch        ; set pixel
mov cx, 20         ; x co-ordinate
mov dx, 20         ; y co-ordinate
int 10h            ; BIOS draw function

mov al, 15         ; color - white
mov ah, 0ch        ; set pixel
mov cx, 21         ; x co-ordinate
mov dx, 21         ; y co-ordinate
int 10h            ; BIOS draw function

mov al, 15         ; color - white
mov ah, 0ch        ; set pixel
mov cx, 22         ; x co-ordinate
mov dx, 22         ; y co-ordinate
int 10h            ; BIOS draw function

mov al, 15         ; color - white
mov ah, 0ch        ; set pixel
mov cx, 23         ; x co-ordinate
mov dx, 23         ; y co-ordinate
int 10h            ; BIOS draw function

mov al, 15         ; color - white
mov ah, 0ch        ; set pixel
mov cx, 24         ; x co-ordinate
mov dx, 24         ; y co-ordinate
int 10h            ; BIOS draw function

mov al, 15         ; color - white
mov ah, 0ch        ; set pixel
mov cx, 25         ; x co-ordinate
mov dx, 25         ; y co-ordinate
int 10h            ; BIOS draw function

mov al, 15         ; color - white
mov ah, 0ch        ; set pixel
mov cx, 26         ; x co-ordinate
mov dx, 26         ; y co-ordinate
int 10h            ; BIOS draw function

mov al, 15         ; color - white
mov ah, 0ch        ; set pixel
mov cx, 27         ; x co-ordinate
mov dx, 27         ; y co-ordinate
int 10h            ; BIOS draw function

mov al, 15         ; color - white
mov ah, 0ch        ; set pixel
mov cx, 28         ; x co-ordinate
mov dx, 28         ; y co-ordinate
int 10h            ; BIOS draw function

mov al, 15         ; color - white
mov ah, 0ch        ; set pixel
mov cx, 29         ; x co-ordinate
mov dx, 29         ; y co-ordinate
int 10h            ; BIOS draw function

mov al, 15         ; color - white
mov ah, 0ch        ; set pixel
mov cx, 30         ; x co-ordinate
mov dx, 30         ; y co-ordinate
int 10h            ; BIOS draw function

mov al, 15         ; color - white
mov ah, 0ch        ; set pixel
mov cx, 31         ; x co-ordinate
mov dx, 31         ; y co-ordinate
int 10h            ; BIOS draw function

mov al, 15         ; color - white
mov ah, 0ch        ; set pixel
mov cx, 32         ; x co-ordinate
mov dx, 32         ; y co-ordinate
int 10h            ; BIOS draw function

mov al, 15         ; color - white
mov ah, 0ch        ; set pixel
mov cx, 33         ; x co-ordinate
mov dx, 33         ; y co-ordinate
int 10h            ; BIOS draw function

mov al, 15         ; color - white
mov ah, 0ch        ; set pixel
mov cx, 34         ; x co-ordinate
mov dx, 34         ; y co-ordinate
int 10h            ; BIOS draw function

mov al, 15         ; color - white
mov ah, 0ch        ; set pixel
mov cx, 35         ; x co-ordinate
mov dx, 35         ; y co-ordinate
int 10h            ; BIOS draw function

mov al, 15         ; color - white
mov ah, 0ch        ; set pixel
mov cx, 36         ; x co-ordinate
mov dx, 36         ; y co-ordinate
int 10h            ; BIOS draw function

mov al, 15         ; color - white
mov ah, 0ch        ; set pixel
mov cx, 37         ; x co-ordinate
mov dx, 37         ; y co-ordinate
int 10h            ; BIOS draw function

mov al, 15         ; color - white
mov ah, 0ch        ; set pixel
mov cx, 38         ; x co-ordinate
mov dx, 38         ; y co-ordinate
int 10h            ; BIOS draw function

mov al, 15         ; color - white
mov ah, 0ch        ; set pixel
mov cx, 39         ; x co-ordinate
mov dx, 39         ; y co-ordinate
int 10h            ; BIOS draw function

mov al, 15         ; color - white
mov ah, 0ch        ; set pixel
mov cx, 40         ; x co-ordinate
mov dx, 40         ; y co-ordinate
int 10h            ; BIOS draw function

mov al, 15         ; color - white
mov ah, 0ch        ; set pixel
mov cx, 41         ; x co-ordinate
mov dx, 41         ; y co-ordinate
int 10h            ; BIOS draw function

mov al, 15         ; color - white
mov ah, 0ch        ; set pixel
mov cx, 42         ; x co-ordinate
mov dx, 42         ; y co-ordinate
int 10h            ; BIOS draw function

mov al, 15         ; color - white
mov ah, 0ch        ; set pixel
mov cx, 43         ; x co-ordinate
mov dx, 43         ; y co-ordinate
int 10h            ; BIOS draw function

mov al, 15         ; color - white
mov ah, 0ch        ; set pixel
mov cx, 44         ; x co-ordinate
mov dx, 44         ; y co-ordinate
int 10h            ; BIOS draw function

mov al, 15         ; color - white
mov ah, 0ch        ; set pixel
mov cx, 45         ; x co-ordinate
mov dx, 45         ; y co-ordinate
int 10h            ; BIOS draw function

mov al, 15         ; color - white
mov ah, 0ch        ; set pixel
mov cx, 46         ; x co-ordinate
mov dx, 46         ; y co-ordinate
int 10h            ; BIOS draw function

mov al, 15         ; color - white
mov ah, 0ch        ; set pixel
mov cx, 47         ; x co-ordinate
mov dx, 47         ; y co-ordinate
int 10h            ; BIOS draw function

mov al, 15         ; color - white
mov ah, 0ch        ; set pixel
mov cx, 48         ; x co-ordinate
mov dx, 48         ; y co-ordinate
int 10h            ; BIOS draw function

mov al, 15         ; color - white
mov ah, 0ch        ; set pixel
mov cx, 49         ; x co-ordinate
mov dx, 49         ; y co-ordinate
int 10h            ; BIOS draw function

mov al, 15         ; color - white
mov ah, 0ch        ; set pixel
mov cx, 50         ; x co-ordinate
mov dx, 50         ; y co-ordinate
int 10h            ; BIOS draw function

mov al, 15         ; color - white
mov ah, 0ch        ; set pixel
mov cx, 51         ; x co-ordinate
mov dx, 51         ; y co-ordinate
int 10h            ; BIOS draw function

mov al, 15         ; color - white
mov ah, 0ch        ; set pixel
mov cx, 52         ; x co-ordinate
mov dx, 52         ; y co-ordinate
int 10h            ; BIOS draw function

mov al, 15         ; color - white
mov ah, 0ch        ; set pixel
mov cx, 53         ; x co-ordinate
mov dx, 53         ; y co-ordinate
int 10h            ; BIOS draw function

mov al, 15         ; color - white
mov ah, 0ch        ; set pixel
mov cx, 54         ; x co-ordinate
mov dx, 54         ; y co-ordinate
int 10h            ; BIOS draw function

mov al, 15         ; color - white
mov ah, 0ch        ; set pixel
mov cx, 55         ; x co-ordinate
mov dx, 55         ; y co-ordinate
int 10h            ; BIOS draw function

mov al, 15         ; color - white
mov ah, 0ch        ; set pixel
mov cx, 56         ; x co-ordinate
mov dx, 56         ; y co-ordinate
int 10h            ; BIOS draw function

mov al, 15         ; color - white
mov ah, 0ch        ; set pixel
mov cx, 57         ; x co-ordinate
mov dx, 57         ; y co-ordinate
int 10h            ; BIOS draw function

mov al, 15         ; color - white
mov ah, 0ch        ; set pixel
mov cx, 58         ; x co-ordinate
mov dx, 58         ; y co-ordinate
int 10h            ; BIOS draw function

mov al, 15         ; color - white
mov ah, 0ch        ; set pixel
mov cx, 59         ; x co-ordinate
mov dx, 59         ; y co-ordinate
int 10h            ; BIOS draw function

mov al, 15         ; color - white
mov ah, 0ch        ; set pixel
mov cx, 60         ; x co-ordinate
mov dx, 60         ; y co-ordinate
int 10h            ; BIOS draw function

mov al, 15         ; color - white
mov ah, 0ch        ; set pixel
mov cx, 61         ; x co-ordinate
mov dx, 61         ; y co-ordinate
int 10h            ; BIOS draw function

mov al, 15         ; color - white
mov ah, 0ch        ; set pixel
mov cx, 62         ; x co-ordinate
mov dx, 62         ; y co-ordinate
int 10h            ; BIOS draw function

mov al, 15         ; color - white
mov ah, 0ch        ; set pixel
mov cx, 63         ; x co-ordinate
mov dx, 63         ; y co-ordinate
int 10h            ; BIOS draw function

mov al, 15         ; color - white
mov ah, 0ch        ; set pixel
mov cx, 64         ; x co-ordinate
mov dx, 64         ; y co-ordinate
int 10h            ; BIOS draw function

mov al, 15         ; color - white
mov ah, 0ch        ; set pixel
mov cx, 65         ; x co-ordinate
mov dx, 65         ; y co-ordinate
int 10h            ; BIOS draw function

mov al, 15         ; color - white
mov ah, 0ch        ; set pixel
mov cx, 66         ; x co-ordinate
mov dx, 66         ; y co-ordinate
int 10h            ; BIOS draw function

mov al, 15         ; color - white
mov ah, 0ch        ; set pixel
mov cx, 67         ; x co-ordinate
mov dx, 67         ; y co-ordinate
int 10h            ; BIOS draw function

mov al, 15         ; color - white
mov ah, 0ch        ; set pixel
mov cx, 68         ; x co-ordinate
mov dx, 68         ; y co-ordinate
int 10h            ; BIOS draw function

mov al, 15         ; color - white
mov ah, 0ch        ; set pixel
mov cx, 69         ; x co-ordinate
mov dx, 69         ; y co-ordinate
int 10h            ; BIOS draw function

mov al, 15         ; color - white
mov ah, 0ch        ; set pixel
mov cx, 70         ; x co-ordinate
mov dx, 70         ; y co-ordinate
int 10h            ; BIOS draw function

mov al, 15         ; color - white
mov ah, 0ch        ; set pixel
mov cx, 71         ; x co-ordinate
mov dx, 71         ; y co-ordinate
int 10h            ; BIOS draw function

mov al, 15         ; color - white
mov ah, 0ch        ; set pixel
mov cx, 72         ; x co-ordinate
mov dx, 72         ; y co-ordinate
int 10h            ; BIOS draw function

mov al, 15         ; color - white
mov ah, 0ch        ; set pixel
mov cx, 73         ; x co-ordinate
mov dx, 73         ; y co-ordinate
int 10h            ; BIOS draw function

mov al, 15         ; color - white
mov ah, 0ch        ; set pixel
mov cx, 74         ; x co-ordinate
mov dx, 74         ; y co-ordinate
int 10h            ; BIOS draw function

mov al, 15         ; color - white
mov ah, 0ch        ; set pixel
mov cx, 75         ; x co-ordinate
mov dx, 75         ; y co-ordinate
int 10h            ; BIOS draw function

mov al, 15         ; color - white
mov ah, 0ch        ; set pixel
mov cx, 76         ; x co-ordinate
mov dx, 76         ; y co-ordinate
int 10h            ; BIOS draw function

mov al, 15         ; color - white
mov ah, 0ch        ; set pixel
mov cx, 77         ; x co-ordinate
mov dx, 77         ; y co-ordinate
int 10h            ; BIOS draw function

mov al, 15         ; color - white
mov ah, 0ch        ; set pixel
mov cx, 78         ; x co-ordinate
mov dx, 78         ; y co-ordinate
int 10h            ; BIOS draw function

mov al, 15         ; color - white
mov ah, 0ch        ; set pixel
mov cx, 79         ; x co-ordinate
mov dx, 79         ; y co-ordinate
int 10h            ; BIOS draw function

mov al, 15         ; color - white
mov ah, 0ch        ; set pixel
mov cx, 80         ; x co-ordinate
mov dx, 80         ; y co-ordinate
int 10h            ; BIOS draw function

mov al, 15         ; color - white
mov ah, 0ch        ; set pixel
mov cx, 81         ; x co-ordinate
mov dx, 81         ; y co-ordinate
int 10h            ; BIOS draw function

mov al, 15         ; color - white
mov ah, 0ch        ; set pixel
mov cx, 82         ; x co-ordinate
mov dx, 82         ; y co-ordinate
int 10h            ; BIOS draw function

mov al, 15         ; color - white
mov ah, 0ch        ; set pixel
mov cx, 83         ; x co-ordinate
mov dx, 83         ; y co-ordinate
int 10h            ; BIOS draw function

mov al, 15         ; color - white
mov ah, 0ch        ; set pixel
mov cx, 84         ; x co-ordinate
mov dx, 84         ; y co-ordinate
int 10h            ; BIOS draw function

ret
times 1024 - ($ - $$) db 0x00

How it look like in hex.

答案

问题的最可能原因是当您清除屏幕时，您正在破坏dl的内容。

当BIOS加载引导扇区然后调用它时，它会将驱动器号放入dl。当您稍后尝试将后续扇区加载到内存中时，必须保留此值以供使用。由于您没有这样做，当您尝试读取驱动器时，BIOS正在尝试从（可能）不存在的设备读取。

另一答案
xor ax, ax                  ; AX=0
mov ds, ax                  ; DS=ES=0 because we use an org of 0x7c00 - Segment<<4+offset = 0x0000<<4+0x7c00 = 0x07c00
mov ax, es
mov ax, ss
mov sp, 0x7c00

设置段寄存器失败！

你需要将AX存储在其中而不是其他方式。

xor ax, ax
mov ds, ax
mov es, ax                    <---
mov ss, ax                    <---
mov sp, 0x7c00 

mov ah, 0x07        ; function to call with interrupt
mov bh, 0x01        ; blue background 
mov dx, 0x3FFF      ; fill whole screen
int 0x10            ; BIOS draw function

你如何画12h的画面是相当奇怪的！

此屏幕有80列和30行，因此右下角位于（79,29）。 你也忘了指定左上角是（0,0）。你的bootloader程序永远不应该依赖于程序启动时具有零值的CX！

mov ah, 0x07        ; function to call with interrupt
mov bh, 0x01        ; blue background 
xor cx, cx          ; (0,0)                       <-----
mov dx, 0x1D4F      ; (79,29)                     <-----
int 0x10            ; BIOS draw function

以上是关于简述代码区的BOOT功能:BOOT0和BOOT1引脚如何控制系统的启动方式?的主要内容，如果未能解决你的问题，请参考以下文章

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