This application is intended to run on ESP8266 module with accessible HSPI interface (e.g. ESP-12).
The application implements custom SPI protocol on HSPI interface of ESP8266 module and enables to use it as a dedicated WiFi slave device - see below. The SPI interface is used because of its strictly master/slave nature.
The newest esp8266/Arduino repository code breaks the app. The problem is in the enum wl_status_t in wl_definitons.h file. The enum has to be the same both in master and slave code. Unfortunately, this enum changed in time in esp8266/Arduino repository. Until a new esp8266/Arduino release comes, you have to use release 2.7.4
If you are really into using the bleeding edge esp8266/Arduino repo, go to WiFiSpi library and change the wl_status_t in wl_definitons.h file according to the esp8266 repo.
Added UDP Multicast support.
Added SSL Client connection using the AxTLS library. Added verifySSL function that verifies server certificate (SHA1 fingerprint and domain name).
Enhanced communications protocol (added CRC-8 and confirmation of message reception). Shortened the status message from 4 bytes to 2 bytes and added XOR check. The protocol version is now 0.2.0 and is incompatible with the former one.
Verified and supported the reset circuit ensuring proper reset of ESP8266 (more here).
The ESP8266 has two SPI interfaces. The first is connected to the flash memory, the second (named HSPI) can be used by user. The HSPI signals are multiplexed with GPIO12-15. Suitable device for the slave is ESP-12.
While this project enables the SPI communication as a slave device, on master devices the corresponding library must be loaded. For Arduino AVR devices the library is WiFiSpi.
The library uses hardware SPI on Arduino so most of the signals are fixed to certain pins.
The wiring is as follows:
PIN | Uno | STM32F103C8 | ESP8266
Name | | SPI1 SPI2 | GPIO NodeMCU
-------+---------+---------------------------------
SS | D10 | PA4 PB12 | 15 D8
MOSI | D11 | PA7 PB15 | 13 D7
MISO | D12 | PA6 PB14 | 12 D6
SCK | D13 | PA5 PB13 | 14 D5
If you are using a reset circuit for proper signals on reset, use GPIO5 as SS_EN output.
Please be careful, the ESP8266 chip ports are NOT 5V tolerant, if you're connecting to a 5V device you have to use a level converter.
The simplest way to do it is to use the Arduino IDE with support for ESP8266.
The Arduino IDE environment is capable to compile and flash programs for ESP8266 modules. The installation process is described on esp8266/arduino github pages.
Don't forget to change the board values in the Arduino environment (menu Tools - Board and next). The application runs fine on minimum setup (512K, no SPIFFS). For flashing you will need to connect the USB to Serial converter to Rx and Tx pins and put CH_PD high (3.3V) and GPIO15 low (GND). Put GPIO0 low (GND) and reset the chip just before flashing begins. This is a standard procedure and you can find details anywhere on the Internet. If you are using modules with USB connection (NodeMCU, e.g.), all you have to do is to connect the module to your USB port.
- SPI protocol optimization
The protocol running on SPI interface was inspired by protocol used in Arduino WiFi library. The code structure and some code is taken from this library, too.
The SPI master code was inspired and parts were taken from the ESPSlave example of the ESP8266 Arduino project.