ESP8266 Boot
目录 |
1 ESP8266 启动
- Reset 入口在: 0x40000080
ESP8266 启动时,将从 UART0 以波特率 74880 打印:
ets Jan 8 2013,rst cause:2, boot mode:(3,6) load 0x40100000, len 30372, room 16 tail 4 chksum 0xe6 load 0x3ffe8000, len 900, room 4 tail 0 chksum 0x0a load 0x3ffe8388, len 392, room 8 tail 0 chksum 0x14 csum 0x14
- Reset Cause
1 ---> Power On 2 ---> External Reset 4 ---> Hardware Watchdog Reset
- chksum 与 csum 值相等,表示启动过程中 Flash 读取正确
写入时:
localhost:hello comcat$ ls -l build/ total 1488 -rw-r--r-- 1 comcat staff 31712 12 5 11:09 0x00000.bin -rw-r--r-- 1 comcat staff 190596 12 5 11:09 0x40000.bin -rwxr-xr-x 1 comcat staff 516521 12 5 11:09 app.out -rw-r--r-- 1 comcat staff 4632 12 5 11:09 app_app.a -rw-r--r-- 1 comcat staff 4480 12 5 11:09 main.o localhost:hello comcat$ make flash ../../../toolchain/bin/esptool -cd nodemcu -cb 115200 -cp /dev/cu.SLAB_USBtoUART -ca 0x00000 -cf build/0x00000.bin -ca 0x40000 -cf build/0x40000.bin Uploading 31712 bytes from build/0x00000.bin to flash at 0x00000000 ............................... Uploading 190596 bytes from build/0x40000.bin to flash at 0x00040000 .................................................................................................................
2 Boot Mode
ESP8266 Reset 后,通过判断如下管脚的状态来决定启动模式:
MTDO GPIO0 GPIO2 Mode Description L L H UART 串口刷机 L H H Flash SPI Flash 正常启动 H x x SDIO SD-card 启动
MTDO 为 GPIO15
启动时串口输出的 'boot mode:(x, y)' , x 的低三位对应 {MTDO, GPIO0, GPIO2}
3 代码流程
ResetHandler (0x40000080) Set interrupt level 1 Set processor modes (see separate section) Copy SROM data to SRAM Goto _start _start Set Ring 0 Clear callback vector Set up stack at 3FFFFFFFh Call main main Initialize UART0 115,200 bps, 8N1 iomux.u0txd &= 0xE4F iomux.gpio2 = (iomux.gpio2 & 0xECF) | 0x100 Processor Modes Only Ring 0 used TLBs (D and I) are set to 00000000h-1FFFFFFFh: Illegal 20000000h-5FFFFFFFh: RWX, Cache Write-Through 60000000h-FFFFFFFFh: RWX, Bypass Cache
4 详细分析
4.1 Flash
SPI Flash 非 OTA 系统,两部分:
0x00000 --- 启动自动加载到 RAM 的部分 0x40000 --- 运行需要后再加载的部分
OTA 系统:
0x00000 --- 启动自动加载到 RAM 的部分,boot.bin (OTA 核心实现在这里) 0x01000 --- 4KB 开始,为运行需要后再加载的部分,user1.bin
所有这两个部分,都是 ESP Firmware 格式 (Little Endian):
- File header
Byte Description 0 Always 0xE9 1 Number of segments 2 SPI Flash Interface (0 = QIO, 1 = QOUT, 2 = DIO, 0x3 = DOUT) 3 High four bits: 0 = 512K, 1 = 256K, 2 = 1M, 3 = 2M, 4 = 4M, Low four bits: 0 = 40MHz, 1= 26MHz, 2 = 20MHz, 0xf = 80MHz 4-7 Entry point 8-n Segments
- Segment
Byte Description 0-3 Memory offset 4-7 Segment size 8...n Data
- Footer
The file is padded with zeros until its size is one byte less than a multiple of 16 bytes. A last byte (thus making the file size a multiple of 16) is the checksum of the data of all segments. The checksum is defined as the xor-sum of all bytes and the byte 0xEF.
4.2 片内 Bootloader
在没有外置 SPI Flash 的情形下,ESP8266 有几个外围支持元件(晶振、电容、电阻),也能启动,其片内有 ROM,带一个很小的 OS(极可能是 XTOS,xtensa 提供的最小系统),可讲其理解为一个片内 Bootloader
这个 Bootloader 实现了很多常用的函数,其内存地址也是固定的,官方 SDK 已经将其导出,参考这个链接脚本:https://github.com/icamgo/noduino-sdk/blob/master/sdk/ld/eagle.rom.addr.v6.ld
这个应该是 ESP8266 最底端的,Reset 异常处理后,首先进入的就是这个 XTOS,在完成的基本系统初始化后,加载 SPI Flash 的第一部分 (0x00000 始)进入 RAM,然后串口输出这类信息:
ets Jan 8 2013,rst cause:2, boot mode:(3,6) load 0x40100000, len 30372, room 16 tail 4 chksum 0xe6 load 0x3ffe8000, len 900, room 4 tail 0 chksum 0x0a load 0x3ffe8388, len 392, room 8 tail 0 chksum 0x14 csum 0x14
4.3 参考
- https://github.com/tommie/esptool
- https://github.com/igrr/esptool-ck
- https://github.com/esp8266/Arduino/blob/master/bootloaders/eboot/rom.ld
- XTOS Reset Vector