NodeMcu除了可以使用自家的nodemcu-firmware － 基于eLua的固件，当然还可以使用基于esp-open-rtos系统的固件。个人还是喜欢使用C语言的esp-open-rtos系统。

• 关于NodeMcu

NodeMcu: ESP8266 & NodeMcu开发入门

• 编译环境搭建

参考：https://github.com/pfalcon/esp-open-sdk/

我这里使用的系统为Mac OS

由于编译esp-open-rtos需要安装esp-open-sdk, 所以我们需要先安装编译esp-open-sdk:

1. 安装编译工具

$ brew tap homebrew/dupes
$ brew install binutils coreutils automake wget gawk libtool help2man gperf gnu-sed --with-default-names grep
$ export PATH="/usr/local/opt/gnu-sed/bin:$PATH"

NOTE:

sed需要使用/usr/local/opt/gnu-sed/bin/sed中的sed, 这与官方的文档稍有出路。

2. 下载并编译esp-open-sdk

$ git clone https://github.com/pfalcon/esp-open-sdk.git
$ cd esp-open-sdk && git checkout b1929e3
$ git submodule update --init

NOTE:

这里我使用的是commit id为b1929e3:

commit b1929e33f41c4bd9715e5f91ab0cf68de5939396
Author: Max Filippov <jcmvbkbc@gmail.com>
Date:   Sun Feb 5 21:02:17 2017 -0800

    examples/blinky: add -lc to LDLIBS for memchr
    
    This fixes issue #213
    
    Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>

如果想使用最新的代码，可以使用如下命令，将esp-open-sdk及其子模块clone下来：

$ git clone --recursive https://github.com/pfalcon/esp-open-sdk.git

3. 编译esp-open-sdk

编译时会从网上下载文件：

esp-open-sdk/crosstool-NG/.build/tarballs/binutils-2.25.1.tar.bz2
esp-open-sdk/crosstool-NG/.build/tarballs/cloog-0.18.4.tar.gz
esp-open-sdk/crosstool-NG/.build/tarballs/expat-2.1.0.tar.gz
esp-open-sdk/crosstool-NG/.build/tarballs/gcc-4.8.5.tar.bz2
esp-open-sdk/crosstool-NG/.build/tarballs/gdb-7.10.tar.xz
esp-open-sdk/crosstool-NG/.build/tarballs/gmp-6.0.0a.tar.xz
esp-open-sdk/crosstool-NG/.build/tarballs/isl-0.14.tar.xz
esp-open-sdk/crosstool-NG/.build/tarballs/mpc-1.0.3.tar.gz
esp-open-sdk/crosstool-NG/.build/tarballs/mpfr-3.1.3.tar.xz
esp-open-sdk/crosstool-NG/.build/tarballs/ncurses-6.0.tar.gz
esp-open-sdk/crosstool-NG/.build/tarballs/newlib-2.0.0.tar.gz
esp-open-sdk/crosstool-NG/.build/tarballs/xtensa_lx106.tar

由https://github.com/SuperHouse/esp-open-rtos/blob/master/README.md可知，编译使用如下命令：

$ make toolchain esptool libhal STANDALONE=n

4. 设置环境变量

编译之后，会在esp-open-sdk/xtensa-lx106-elf/bin所需的编译工具及固件更新工具esptool.py，将这个路径加入PATH:

$ export PATH=`pwd`/xtensa-lx106-elf/bin:$PATH

• 代码下载

参考：https://github.com/SuperHouse/esp-open-rtos/blob/master/README.md

$ git clone https://github.com/Superhouse/esp-open-rtos.git
$ cd esp-open-rtos && git checkout f51a210
$ git submodule update --init

NOTE:

我这里使用的commit id为f51a210：

commit f51a2109b1c1a3b4a712b93c5a50d0aa2553fa6f
Author: Zaltora <lilian.marazano@gmail.com>
Date:   Tue Feb 21 20:44:03 2017 +0100

    CRC library (#339)
    
    * Crc initial example
    * Update example and fix submodule

• 编译

在esp-open-rtos/example中包含有sample code, 可以编译出来看看：

Makefile            ds1302_test         http_get_mbedtls    pwm_test            tests
access_point        ds1307              http_server         sdio_raw            tls_server
ads1115_test        ds18b20_broadcaster i2c_lcd_test        serial_echo         tls_server_bearssl
aws_iot             ds18b20_onewire     i2s_audio           simple              tsl2561
blink               ds3231_test         ina3221_test        simple_cplusplus    ultrasonic
blink_timers        experiments         json_jsmn_simple    sntp                wifi_scan
bmp180_i2c          fatfs               max7219_7seg        spi_test            ws2812_i2s
bmp280              fatfs_rtc           mcp4725_test        spiffs              ws2812_rainbow
button              hd44780_lcd         mqtt_client         ssd1306_example
cpp_01_tasks        hmc5883l            ms561101ba03        ssd1306_fps
crc_example         http_get            ota_basic           sysparam_editor
dht_sensor          http_get_bearssl    pca9685_pwm         terminal

对于需要WiFi的例子，如access_point，需要添加include/private_ssid_config.h文件，包含如下内容：

#define WIFI_SSID "mywifissid"
#define WIFI_PASS "my secret password"

编译命令如下：

$ make -C examples/access_point/

• 固件更新

可通过如下命令：

$ make -C examples/access_point/ ESPPORT=/dev/cu.SLAB_USBtoUART flash
esptool.py -p /dev/cu.SLAB_USBtoUART --baud 115200 write_flash -fs 16m -fm qio -ff 40m \
		0x0 ../../bootloader/firmware_prebuilt/rboot.bin 0x1000 ../../bootloader/firmware_prebuilt/blank_config.bin 0x2000 ./firmware/access_point.bin 
esptool.py v1.2
Connecting...
Running Cesanta flasher stub...
Flash params set to 0x0030
Writing 4096 @ 0x0... 4096 (100 %)
Wrote 4096 bytes at 0x0 in 0.4 seconds (90.1 kbit/s)...
Writing 4096 @ 0x1000... 4096 (100 %)
Wrote 4096 bytes at 0x1000 in 0.4 seconds (90.0 kbit/s)...
Writing 249856 @ 0x2000... 249856 (100 %)
Wrote 249856 bytes at 0x2000 in 21.7 seconds (92.0 kbit/s)...
Leaving...

可以看到这里使用esptool.py(https://github.com/espressif/esptool)脚本对固件进行更新：

－ -fs 16m：flash size 为16MiB(?)

－ -fm qio：flash mode为qio (https://nodemcu.readthedocs.io/en/master/en/flash/)

－ -ff 40m: flash frequency为40Mhz

• 相关的参考文档

1. https://github.com/pfalcon/esp-open-sdk/
2. https://github.com/SuperHouse/esp-open-rtos
3. https://github.com/nodemcu/nodemcu-firmware
4. https://github.com/espressif/esptool