很久没研究ESP32了，这里简单更新一下ESP32的学习笔记，这一节研究下ESP32的串口打印输出的功能！
对串口比较熟悉的朋友应该知道，串口是一个常用的接口。在ESP8266中，就有两个串口，一个用来打印工作状态，另一个的RXD管脚和外部的SPI复用了，所以只能用TXD，也就是ESP8266只有一个半串口能用。
相比ESP8266，ESP32的串口终于变成了两个完整的，分别是UART0和UART1。其中，UART0用来打印log信息，UART1用来处理AT指令。所以使用时千万要注意，经常有人在UART0上测试AT指令没反应，因为你找错了串口。
接下来开始演示例程，因为官方的SDK里面已经包含了大量现成的例子，我们直接使用就行。
复制工程ESP32_LED，粘贴时修改工程名称为ESP32_HELLO_WORLD。因为我们要使用的是SDK目录下的例程：
examples\get-started\hello_world
所以要修改下面的信息：
然后，打开工程，如果你觉得blink例程碍事的话，可以把它删除。
打开hello_world_main.c文件，内容如下：
官方提供了一个完整的串口打印例程，可以打印CPU的相关信息。
不需要做修改，clean、build一下，生成.bin文件。
使用ESPFlashDownloadTool_v3.6.4工具进行下载，注意地址和路径，如下：
下载成功后，重新上电，可以看到串口打印信息。如下图所示：
前面是上电的时候，系统打印的启动信息。从“hello world”开始，是例程里写到的信息。具体内容如下：
ets Jun 8 2016 00:22:57
rst:0xc (SW_CPU_RESET),boot:0x13 (SPI_FAST_FLASH_BOOT)
configsip: 0, SPIWP:0xee
clk_drv:0x00,q_drv:0x00,d_drv:0x00,cs0_drv:0x00,hd_drv:0x00,wp_drv:0x00
mode:DIO, clock div:2
load:0x3fff0018,len:4
load:0x3fff001c,len:6924
load:0x40078000,len:14680
load:0x40080400,len:4312
entry 0x400806e8
[0;32mI (72) boot: Chip Revision: 1[0m
[0;32mI (72) boot_comm: mismatch chip revision, expect 1, found 0[0m
[0;32mI (39) boot: ESP-IDF v4.1-dev-437-gd2ad0f077-dirty 2nd stage bootloader[0m
[0;32mI (39) boot: compile time 22:39:49[0m
[0;32mI (40) boot: Enabling RNG early entropy source...[0m
[0;32mI (45) boot: SPI Speed : 40MHz[0m
[0;32mI (50) boot: SPI Mode : DIO[0m
[0;32mI (54) boot: SPI Flash Size : 4MB[0m
[0;32mI (58) boot: Partition Table:[0m
[0;32mI (61) boot: ## Label Usage Type ST Offset Length[0m
[0;32mI (69) boot: 0 nvs WiFi data 01 02 00009000 00006000[0m
[0;32mI (76) boot: 1 phy_init RF data 01 01 0000f000 00001000[0m
[0;32mI (83) boot: 2 factory factory app 00 00 00010000 00100000[0m
[0;32mI (91) boot: End of partition table[0m
[0;32mI (95) boot_comm: mismatch chip revision, expect 1, found 0[0m
[0;32mI (101) esp_image: segment 0: paddr=0x00010020 vaddr=0x3f400020 size=0x08c90 ( 35984) map[0m
[0;32mI (123) esp_image: segment 1: paddr=0x00018cb8 vaddr=0x3ffb0000 size=0x02188 ( 8584) load[0m
[0;32mI (127) esp_image: segment 2: paddr=0x0001ae48 vaddr=0x40080000 size=0x00400 ( 1024) load[0m
[0;32mI (131) esp_image: segment 3: paddr=0x0001b250 vaddr=0x40080400 size=0x04dc0 ( 19904) load[0m
[0;32mI (148) esp_image: segment 4: paddr=0x00020018 vaddr=0x400d0018 size=0x12eb4 ( 77492) map[0m
[0;32mI (175) esp_image: segment 5: paddr=0x00032ed4 vaddr=0x400851c0 size=0x044b0 ( 17584) load[0m
[0;32mI (189) boot: Loaded app from partition at offset 0x10000[0m
[0;32mI (189) boot: Disabling RNG early entropy source...[0m
[0;32mI (189) cpu_start: Pro cpu up.[0m
[0;32mI (193) cpu_start: Application information:[0m
[0;32mI (198) cpu_start: Project name: hello-world[0m
[0;32mI (203) cpu_start: App version: v4.1-dev-437-gd2ad0f077-dirty[0m
[0;32mI (210) cpu_start: Compile time: Apr 6 2020 22:40:08[0m
[0;32mI (216) cpu_start: ELF file SHA256: 44b2fd949d57ea5c...[0m
[0;32mI (222) cpu_start: ESP-IDF: v4.1-dev-437-gd2ad0f077-dirty[0m
[0;32mI (229) cpu_start: Starting app cpu, entry point is 0x40080fb8[0m
[0;32mI (216) cpu_start: App cpu up.[0m
[0;32mI (240) heap_init: Initializing. RAM available for dynamic allocation:[0m
[0;32mI (246) heap_init: At 3FFAE6E0 len 00001920 (6 KiB): DRAM[0m
[0;32mI (252) heap_init: At 3FFB3170 len 0002CE90 (179 KiB): DRAM[0m
[0;32mI (259) heap_init: At 3FFE0440 len 00003AE0 (14 KiB): D/IRAM[0m
[0;32mI (265) heap_init: At 3FFE4350 len 0001BCB0 (111 KiB): D/IRAM[0m
[0;32mI (271) heap_init: At 40089670 len 00016990 (90 KiB): IRAM[0m
[0;32mI (278) cpu_start: Pro cpu start user code[0m
[0;32mI (296) spi_flash: detected chip: generic[0m
[0;32mI (296) spi_flash: flash io: dio[0m
[0;32mI (297) cpu_start: Starting scheduler on PRO CPU.[0m
[0;32mI (0) cpu_start: Starting scheduler on APP CPU.[0m
Hello world!
This is ESP32 chip with 2 CPU cores, WiFi/BT/BLE, silicon revision 1, 4MB external flash
Restarting in 10 seconds...
Restarting in 9 seconds...
Restarting in 8 seconds...
Restarting in 7 seconds...
Restarting in 6 seconds...
Restarting in 5 seconds...
Restarting in 4 seconds...
Restarting in 3 seconds...
Restarting in 2 seconds...
Restarting in 1 seconds...
Restarting in 0 seconds...
串口的例程总体来说比较简单，官方已经帮我们写好了。如果没有特殊需求的话，不做修改，直接就能使用，波特率默认115200.
需要例程的话，公众号（单片机爱好者）后台回复关键词：ESP32_HELLO_WORLD，即可获得下载链接。不过，这么简单的例程，应该自己能搞定吧！