This application note explains how to run a sample TCP server with the WiFi ESP Click card, from the FreeRTOS demo application.

1. Understanding WiFi ESP Click Interfaces

1.1. FreeRTOS WiFi ESP Click Implementation

The FreeRTOS BSP makes use of the STM32CubeH7 software component to provide a device driver for the WiFi ESP Click. The driver is configured (enabled / disabled) at the BSP build time, using the WIFIESP_MODULE_ENABLED and HAL_UART_MODULE_ENABLED configuration option, defined in the stm32h7xx_hal_conf.h file.

1.2. FreeRTOS WiFi ESP Click C-Binding API

The WiFi ESP Click driver implements the following C-binding API:

Function	Description	Comments
`int32_t wifiesp_init(wifiesp_handler *ctx);`
	Initialize WiFi ESP Click	`ctx` is the WiFi ESP Click handle
`void wifiesp_deinit(wifiesp_handler *ctx);`
	De-initialise WiFi ESP Click	`ctx` is the WiFi ESP Click handle
`void wifiesp_enable(wifiesp_handler *ctx);`
	Enable WiFi ESP Click	`ctx` is the WiFi ESP Click handle
`void wifiesp_disable(wifiesp_handler *ctx);`
	Disable WiFi ESP Click	`ctx` is the WiFi ESP Click handle
`int32_t wifiesp_generic_write(wifiesp_handler ctx, char data_buf, uint16_t len, uint32_t timeout);`
	Send an amount of data	`ctx` is the WiFi ESP Click handle; `data_buf` is the pointer to data buffer; `len` is the amount of bytes to be sent; `timeout` is the amount of ticks that the driver waits for a response from UART; returns a number of transmitted bytes or a negative error code
`int32_t wifiesp_generic_read(wifiesp_handler ctx, char data_buf, int32_t max_len, uint32_t timeout);`
	Receive an amount of data	`ctx` is the WiFi ESP Click handle; `data_buf` is the pointer to data buffer; `max_len` is the max amount of bytes to be received; `timeout` is the amount of ticks that the driver waits for data from UART
`int32_t wifiesp_send_cmd(wifiesp_handler ctx, char cmd, char *args);`
	Send a command	`ctx` is the WiFi ESP Click handle; `cmd` is the pointer to command string; `args` is the pointer to the command arguments; returns a number of transmitted bytes or a negative error code

The wifiesp_handler data structure used in the driver API has the following definition:

typedef struct
{
    uint8_t is_enabled; /* Enable flag */
    uart_handler *uart; /* UART handle for communication with the WiFi ESP Click */

} wifiesp_handler;

1.3. FreeRTOS WiFi ESP Click Macros

The WiFi ESP Click driver provides the following macros for AT instructions:

Macro	Instruction	Description
`WIFIESP_CHECK`	AT	Test AT startup
`WIFIESP_RESTORE`	AT+RESTORE	Factory reset
`WIFIESP_RST`	AT+RST	Restart module
`WIFIESP_CHECK_FIRMWARE`	AT+GMR	View version info
`WIFIESP_SET_MODE`	AT+CWMODE	Set WiFi mode without writing to Flash
`WIFIESP_CONNECT_AP`	AT+CWJAP_CUR	Connect to AP without writing the SSID and passphrase to Flash
`WIFIESP_LIST_AP`	AT+CWLAP	List available APs
`WIFIESP_QUIT_AP`	AT+CWQAP	Disconnect from AP
`WIFIESP_SET_AP_PARAMETERS`	AT+CWSAP_CUR	Configuration of softAP mode without writing to Flash
`WIFIESP_JOINED_DEV_IP`	AT+CWLIF	Get station’s IP which is connected to the soft-AP
`WIFIESP_CONNESTION_STATUS`	AT+CIPSTATUS	Check network connection status
`WIFIESP_START`	AT+CIPSTART	Establish TCP connection, UDP transmission or SSL connection
`WIFIESP_MODE`	AT+CIPMODE	Set transfer mode
`WIFIESP_SEND`	AT+CIPSEND	Send data
`WIFIESP_CLOSE`	AT+CIPCLOSE	Close TCP, UDP or SSL connection
`WIFIESP_GET_IP`	AT+CIFSR	Get local IP address
`WIFIESP_SET_DHCP`	AT+CWDHCP_CUR	Enable/Disable DHCP
`WIFIESP_SET_STATION_IP`	AT+CIPSTA_CUR	Set IP address of station
`WIFIESP_GET_STATION_IP`	AT+CIPSTA_CUR?	Get IP address of station
`WIFIESP_SET_MULTIPLE_CONNECTION`	AT+CIPMUX	Enable multiple connections for server
`WIFIESP_SET_AS_SERVER`	AT+CIPSERVER	Configure as TCP server
`WIFIESP_SET_SERVER_TIMEOUT`	AT+CIPSTO	Set TCP server timeout in seconds
`WIFIESP_GET_SERVER_TIMEOUT`	AT+CIPSTO?	Get TCP server timeout
`WIFIESP_PING`	AT+PING	Function Ping

Refer to ESP8266 AT Instruction Set for details about AT instructions.

2. Understanding TCP/IP support in FreeRTOS

2.1. FreeRTOS TCP/IP Support Implementation

The FreeRTOS BSP makes use of the WiFi ESP Click driver to provide TCP/IP support by sending AT instructions to the ESP8266 controller.

2.2. FreeRTOS TCP/IP Instructions Examples

The following are the examples of using the WiFi ESP Click driver to support TCP/IP in FreeRTOS:

Example	Description	Comments
`wifiesp_send_cmd(&wifiesp, WIFIESP_SET_MULTIPLE_CONNECTION, "<mode>");`
	Enable/disable multiple connections	The module responds OK if the mode set successfully and `ERROR` otherwise. Recommended mode for a TCP server is 1 (multiple connections enabled).
`wifiesp_send_cmd(&wifiesp, WIFIESP_SET_AS_SERVER, "1,<port>");`
	Start a TCP server with given port	The module responds OK if the server started successfully and `ERROR` otherwise.
`wifiesp_send_cmd(&wifiesp, WIFIESP_START, "\"TCP\",\"<IP>\",<port>");`
	Connect to a TCP server	The module responds OK if the server started successfully and `ERROR` otherwise, If TCP is connected already, returns `ALREADY CONNECT`.
`wifiesp_send_cmd(&wifiesp, WIFIESP_START, "<link ID>,\"UDP\",\"\<IP>",<port>,<local port>,0");`
	Register UDP ports	The module responds `OK` if the server started successfully and `ERROR` otherwise, If the "connection" already exists, returns `ALREADY CONNECT`. The module will send datagrams to the given `<IP>`; `<local port>` is required for receiving datagrams from remote host.
`wifiesp_send_cmd(&wifiesp, WIFIESP_SEND, "<link ID>,<data len>");`
	Send data to the remote host via TCP or UDP	The module responds `>`, which means that it is ready to send data. The data should be sent to the module without carriage return. If the number of bytes sent are more than the size defined by `<data len>`, the system will reply busy, send the first `<data len>` bytes and after sending the first `<data len>` bytes, the system will reply `SEND OK`. `<link ID>` can be omitted for a TCP client or in single connection mode.
`wifiesp_send_cmd(&wifiesp, WIFIESP_CLOSE, "<link ID>");`
	Close TCP connection or end UDP transmission	The module responds `<link ID>`, `CLOSED` and `OK` if the connection closed correctly and ERROR otherwise. `<link ID>` can be omitted for a TCP client or in single connection mode.

3. Understanding Sample TCP Server

3.1. Sample TCP Server Implementation

The FreeRTOS test application implements a separate thread called WiFi Thread, which provides a sample TCP server utilizing the WiFi ESP Click board.

The sample TCP Server functions as follows:

Read the SSID and passphrase from the U-Boot Environment variables wifi_ssid and wifi_passwd.
Initialize the WiFi ESP Click driver and start communications with the WiFi ESP Click board via UART.
Attempt to connect to the assigned AP (Access Point) and obtain an IP address via DCHCP.
Start the TCP server with the port 80, on the IP address obtained in the previous step, and run the endless loop that waits for connections. Having established a connection, it prints the received messages to the console and sends received data back to the connected client.

3.2. Sample TCP Server Sessions

Perform the following step-wise procedure, to validate the sample TCP server functionality:

Connect the WiFi ESP Click module to the CLICK interface of the STM32H7-BSB Rev 2A board.
Power cycle the board and let it boot to the U-Boot command line.

Set the wifi_ssid and wifi_passwd variables in the U-Boot environment:

STM32H7-SOM U-Boot > setenv wifi_ssid testssid
STM32H7-SOM U-Boot > setenv wifi_passwd testpass
STM32H7-SOM U-Boot > saveenv

Power cycle the board and let it boot to the FreeRTOS CLI.

Validate that the FreeRTOS BSP prints out the following message with the correct SSID and passphrase:

Starting kernel ...

STM32H7 SOM FreeRTOS CLI, http://www.emcraft.com 
Type help to view a list of available commands.
Connecting to WiFi AP testssid with passphrase testpass

Validate that the FreeRTOS BSP prints out the following message after several seconds:

CLI> AT+CWJAP_CUR="testssid","testpass"
WIFI DISCONNECT
WIFI CONNECTED
WIFI GOT IP

OK

WiFi connected
Starting TCP Server
AT+CIFSR
+CIFSR:STAIP,"192.168.0.252"
+CIFSR:STAMAC,"8c:aa:b5:14:89:d2"

OK

TCP Server started
Please connect to the IP address listed above

From a Linux PC machine, connect to the TCP server via telnet or nc:

$ telnet 192.168.0.252 80
Trying 192.168.0.252...
Connected to 192.168.0.252.
Escape character is '^]'.

Send a message to the target and validate that the server sends the received message back:

$ telnet 192.168.0.252 80
Trying 192.168.0.252...
Connected to 192.168.0.252.
Escape character is '^]'.
HELLO
HELLO
TEST
TEST
12345
12345

The server will close the connection if it does not receive any data in several seconds:
```
Connection closed by foreign host.
```

Using Mikroe WiFi ESP Click in FreeRTOS