I recently started experimenting with the ESP8266 module, primarily for communication between two ESP8266 devices. The main goal was to configure one as an Access Point (AP) and the other as a Station (STA), enabling them to communicate over a wireless network. Since the module comes with factory firmware, I mainly used a serial port debugging tool to send AT commands and configure the necessary settings.
**Basic Configuration of ESP8266 and Serial Communication**
**AP Mode (Server): The steps are as follows:**
1. Set the ESP8266 to AP mode using the command `AT+CWMODE=2`. If it was previously configured, you can reset it to factory settings with `AT+RESTORE`.
2. Configure the AP's SSID and password using `AT+CWSAP="ssid","pwd","chl","ecn"`.
3. Restart the module with `AT+RST`.
4. Enable multiple connections by setting `AT+CIPMUX=1`.
5. Start a TCP server on port 5000 using `AT+CIPSERVER=1,5000`.
6. Check the local IP address with `AT+CIFSR` to help the client connect later.
7. Send data using `AT+CIPSEND="link.ID", "length"` once a client connects.
**STA Mode (Client): The steps are as follows:**
1. Switch to STA mode with `AT+CWMODE=1`.
2. Restart the module with `AT+RST`.
3. Connect to the AP using `AT+CWJAP="ssid","pwd"`.
4. Establish a TCP connection with `AT+CIPSTART="type","remote IP","remote port"`. Once connected, you can send data using `AT+CIPSEND`.
5. Set the transmission mode with `AT+CIPMODE=1`.
6. Send data using `AT+CIPSEND`.
Here’s an example of the AP sending data to the STA via the serial port. Before sending each message, you must use `AT+CIPSEND="link.ID", "length"`. In the image, two messages were sent, resulting in 16 bytes total.
For the STA sending data to the AP, since it's in transparent mode, you only need to send `AT+CIPSEND` once. No further commands are needed after that. In the image, three consecutive `AT+CIPSEND` commands were issued along with the message "Hello".
**ESP8266 SDK Serial Interrupt Reception and Transmission**
**1. Transmission**
To start, initialize the serial port using `uart_init(115200, 115200);`, which sets the baud rate for UART0 and UART1. You can then use `uart0_tx_buffer(uint8 *buf, uint16 len)` to send data through UART0. Alternatively, you can use `os_printf()` to print messages, but be cautious if you're using UART1.
If you want to redirect `os_printf()` output to UART1, you can change the default output using `Os_install_putc1((void *)uart1_write_char);`.
**2. Reception**
In the serial initialization function `uart_init()`, there is a task created for receiving data: `system_os_task(uart_recvTask, uart_recvTaskPrio, uart_recvTaskQueue, uart_recvTaskQueueLen);`. This task listens for incoming data on UART0.
The serial port is configured with `uart_config(UART0);`, and an interrupt handler is attached using `ETS_UART_INTR_ATTACH(uart0_rx_intr_handler, &(UartDev.rcv_buff));`.
Inside the interrupt handler, the system checks for various flags. When the receive FIFO timeout occurs (`UART_RXFIFO_TOUT_INT_ST`), it sends a message to the `uart_recvTask` via `system_os_post()`.
In the `uart_recvTask` function, the received data is processed. If buffer mode is enabled, it uses `uart_rx_buff_enq()` to enqueue the data. Otherwise, it reads the FIFO directly, processes each byte, and sends it back using `uart_tx_one_char(UART0, d_tmp)`.
You can modify this code to store the received data in a buffer instead of immediately echoing it, allowing for custom processing or storage.
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