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基于树莓派的嵌入式linux操作系统设计
目录
基于树莓派的嵌入式linux操作系统设计 1
一、设计目的和要求 1
 First stage bootloader 1
二、设计思路与方法 6
三、实现的功能及说明 27
在此简单设计了GPIO的功能用于提示系统状态 28
四、使用 29
五、核心源程序代码和界面图 35
六、实现 37
七、心得体会 40

一、设计目的和要求
1.设计目的
树莓派 OS需要有自己的调度程序。如果实现一个调度程序，还必须处理定时器中断。定时器中断意味着操作系统应该支持一些驱动程序并提供系统调用以将它们暴露给用户应用程序。在此基础上编写驱动程序使之在屏幕上写入内容并从键盘读取用户输入的指令。此外，操作系统需要能够加载和执行用户程序，因此需要支持某种文件系统并能够理解某种可执行文件格式。
树莓派搭载了一枚ARM架构64位4核心SOC（BCM2835）主频为700MHZ,SOC为片上操作系统支持精简指令集，并且板载了512MB DDR2内存。该单板机系统支持SD卡Boot启动。在BCM2835启动时会通过Boot目录启动。树莓派启动分为以下步骤
First stage bootloader
树莓派上电后，SoC 中的 bootloader 首先被执行，其作用是挂载 SD 卡上的 FAT32 分区，从而加载下一阶段的 bootloader。这部分程序被固化在 SoC 的 ROM 中，用户无法修改。
Second stage bootloader (bootcode.bin)
这个阶段的 bootloader 会从 SD 卡上检索 GPU 固件，将固件写入 GPU，随后启动 GPU。
GPU firmware (start.elf)
本阶段中，GPU 启动后会检索附加配置文件（config.txt、fixup.dat），根据其内容设置 CPU 运行参数及内存分配情况，随后将用户代码加载至内存，启动 CPU。
User code (kernel8.img)
通常情况下，CPU 启动后便开始执行 kernel8.img 中的指令，初始化操作系统内核，在某些情况下，也可以被 U-BOOT 代替，由 U-BOOT 来加载内核。在树莓派 1 代中，User code 部分被保存在 kernel.img 文件中，2 代中，该文件更名为 kernel7.img，3 代中，该文件更名为 kernel8.img，本课程设计的全部工作，都在该文件上完成。
综上所述，树莓派上电后的初始化工作大多是在 GPU 中完成的（GPU 内的一颗 RSIC 核心用于完成这些操作）。目前树莓派的 GPU bootloader 仍未开源，只以二进制形式发布，因此本课程设计使用了官
方提供的raspberrypi/firmware官方仓库中的bootcode.bin 和 start.elf，直接复制到 SD 卡Boot目录。
树莓派刻录了官方镜像以后boot分区文件展示。我们自制的操作系统会编译成kernel.Img文件替代官方的kernel.img文件。
二、设计思路与方法
1.设计操作系统的基础依赖
本课程设计要完成多进程与内存管理，需要系统时钟定时器和中断。故设计了定时器和中断函数并设置寄存器。
1.1中断向量

• 树莓派Zero搭载的是BCM2835的处理器。BMC2835 ARM1176 是ARMv6版本的。在默认条件下，处理器加电后会自动加载SD卡中的kernel.img到内存0x8000处。
• ARM的中断向量是在地址0x00 - 0x20
• 0x00 复位 reset
• 0x04 未定义指令
• 0x08 软终端 SWI
• 0x0c 指令预取指
• 0x10 数据访问中止
• 0x14 保留
• 0x18 IRQ
• 0x1c FIQ
  所以内核加载到内存做的第一件事应该是设置好中断向量。
  ARM外设中断表：
  

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0x18 ./object/UART.o colorRed 0x3 ./object/Graphic.o MSG_list 0x4 ./object/Graphic.o input_buf_p 0x40 ./object/UART.o PicLayerTable 0x4 ./object/Graphic.o GpuInfoAddr 0x4 ./object/Graphic.o transparent 0x3 ./object/Graphic.o FreeMemoryTables_p 0x8014 ./object/memory.o MSG_list_ll 0x804 ./object/Graphic.o MouseHaldle 0x4 ./object/Graphic.o colorBule 0x3 ./object/Graphic.o os_timer_ctrl 0xc04 ./object/timer.o colorBlack 0x3 ./object/Graphic.o task_table 0x4c8 ./object/Graphic.o rxtail 0x4 ./object/UART.o task_info 0x154 ./object/Graphic.o rxbuffer 0x1000 ./object/UART.o colorF 0x3 ./object/Graphic.o MSG 0x200 ./object/Graphic.o Memory Configuration Name Origin Length Attributes *default* 0x0000000000000000 0xffffffffffffffff Linker script and memory map [!provide] PROVIDE (__executable_start, 0x8000) 0x0000000000008000 . = 0x8000 .interp *(.interp) .note.gnu.build-id *(.note.gnu.build-id) .hash *(.hash) .gnu.hash *(.gnu.hash) .dynsym *(.dynsym) .dynstr *(.dynstr) .gnu.version 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*(.rela.ctors) .rel.dtors *(.rel.dtors) .rela.dtors *(.rela.dtors) .rel.got *(.rel.got) .rela.got *(.rela.got) .rel.bss *(.rel.bss .rel.bss.* .rel.gnu.linkonce.b.*) .rela.bss *(.rela.bss .rela.bss.* .rela.gnu.linkonce.b.*) .rel.iplt 0x0000000000008000 0x0 [!provide] PROVIDE (__rel_iplt_start, .) *(.rel.iplt) .rel.iplt 0x0000000000008000 0x0 ./object/Graphic.o [!provide] PROVIDE (__rel_iplt_end, .) .rela.iplt 0x0000000000008000 0x0 [!provide] PROVIDE (__rela_iplt_start, .) *(.rela.iplt) [!provide] PROVIDE (__rela_iplt_end, .) .rel.plt *(.rel.plt) .rela.plt *(.rela.plt) .init *(SORT(.init)) .plt *(.plt) .iplt 0x0000000000008000 0x0 *(.iplt) .iplt 0x0000000000008000 0x0 ./object/Graphic.o .text 0x0000000000008000 0xfceb0 *(.text.unlikely .text.*_unlikely .text.unlikely.*) *(.text.exit .text.exit.*) *(.text.startup .text.startup.*) .text.startup 0x0000000000008000 0xcc /tmp/cclqMRGF.o 0x0000000000008000 _start 0x0000000000008088 _get_stack_pointer 0x0000000000008094 _enable_interrupts 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draw_to_screen 0x000000000000a268 draw_to_screen_rect 0x000000000000a410 PicLayerTable_init 0x000000000000a4c8 add_pic 0x000000000000a5e4 add_pic_to_layer 0x000000000000a6e4 rm_picture 0x000000000000a78c rm_from_layer 0x000000000000a954 get_LayerIndex_by_PicIndex 0x000000000000a9a4 get_PicIndex_by_LayerIndex 0x000000000000a9e4 set_pic_to_top 0x000000000000abbc set_picture_position 0x000000000000ace4 pic_layer_reflash_rect 0x000000000000aeb8 pic_layer_reflash 0x000000000000af90 is_inside 0x000000000000b074 inside_rect 0x000000000000bb40 move_pic_layer 0x000000000000c1c4 move_pic_layer_sub 0x000000000000c404 copy_bmp_to_piclayer .text 0x000000000000c5e8 0x103c ./object/linkedlist.o 0x000000000000c5e8 ll_init 0x000000000000c664 ll_add_to_head 0x000000000000c744 ll_add_to_tail 0x000000000000c834 ll_add_by_order 0x000000000000c9c4 ll_add_after_id 0x000000000000cb14 ll_remove_by_id 0x000000000000cbf8 ll_remove_head 0x000000000000cc30 ll_remove_tail 0x000000000000cc78 ll_get_next_id 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