NodeMCU is an open source IoT platform including a firmware which runs on the ESP8266 with the Espressif Non-OS SDK, and hardware based on the ESP-12 module. The device features 4MB of flash memory, 80MHz of system clock, around 50k of usable RAM and an on chip Wifi Transceiver.
The NodeMCU v2 device features a 4 MB (32 Mb) flash memory organized in sectors of 4k each. The flash memory address starts at 0x40200000 and can be read and written from a Zerynth program using the internal flash module.
If flash memory must be used in a Zerynth program, it is recommended to begin using it from secure addresses towards the end the bytecode (start address of the bytecode can be found in the log console of Zerynth Studio during the uplink operation), leaving a minimum safe place to minimize the chance of clashes.
The internal flash of NodeMCU can be organized in different ways. The standard VM is a non-FOTA VM with the VM code beginning at 0x0000, followed by the esp8266 ir0m image at 0x20000 and the esp_init_data at 0x3fc000. The VM is based on the Espressif RTOS SDK 1.4.1.
Microcontroller: Tensilica 32-bit RISC CPU Xtensa LX106
Operating Voltage: 3.3V
Input Voltage: 7-12V
Digital I/O Pins (DIO): 16
Analog Input Pins (ADC): 1
Flash Memory: 4 MB
SRAM: 64 KB
Clock Speed: 80 Mhz
Wi-Fi: IEEE 802.11 b/g/n:
- Integrated TR switch, balun, LNA, power amplifier and matching network
- WEP or WPA/WPA2 authentication, or open networks
Power to the NodeMCU v2 is supplied via the on-board USB Micro B connector or directly via the “VIN” pin. The power source is selected automatically.
The device can operate on an external supply of 6 to 20 volts. If using more than 12V, the voltage regulator may overheat and damage the device. The recommended range is 7 to 12 volts.
Connect, Register, Virtualize and Program¶
The NodeMCU v2 exposes the serial port of the ESP8266 module via a CP2102 usb bridge which is also connected to the boot pins of the module, allowing for a seamless virtualization of the device.
Drivers for the bridge can be downloaded here and are needed for Windows and Mac platforms.
For Linux Platform: to allow the access to serial ports the user needs read/write access to the serial device file. Adding the user to the group, that owns this file, gives the required read/write access:
- Ubuntu distribution –> dialout group
- Arch Linux distribution –> uucp group
Once connected to a USB port the NodeMCU v2 device can be seen as a Virtual Serial port and it is automatically recognized by Zerynth Studio. The next steps are:
- Select the NodeMCU on the Device Management Toolbar;
- Register the device by clicking the “Z” button from the Zerynth Studio;
- Create a Virtual Machine for the device by clicking the “Z” button for the second time;
- Virtualize the device by clicking the “Z” button for the third time.
No user intervention on the device is required for registration and virtualization process
After virtualization, the NodeMCU v2 device is ready to be programmed and the Zerynth scripts uploaded. Just Select the virtualized device from the “Device Management Toolbar” and click the dedicated “upload” button of Zerynth Studio.
No user intervention on the device is required for the upload process.
To exploit the Wi-Fi chip functionalities of the NodeMCU, the lib.espressif.esp8266wifi library must be installed (some example code is provided).
Firmware Over the Air update (FOTA)¶
The Firmware Over the Air feature allows to update the device firmware at runtime. Zerynth FOTA in the NodeMCU v2 device is available for bytecode only.
Flash Layout is shown in table below:
|0x40270000||256Kb||Bytecode Slot 0|
|0x402B0000||320Kb||Bytecode Slot 1|
FOTA Record (small segment of memory where the current and desired state of the firmware is store) for the NodeMCU v2 device is allocated in the RTC memory.