How to add user-defined AT commands

This document details how to add a user-defined AT command based on the esp-at project. It uses the AT+TEST command as an example to show the sample code for each step.

Customizing a basic and well-functioned command requires at least the two steps below:

• Define AT Commands
• Register AT Commands

This step checks how the newly defined command works out.

• Give it a try

The remaining steps are for relatively complex AT commands and are optional depending on your needs.

• Define Return Values
• Access Command Parameters
• Omit Command Parameters
• Block Command Execution
• Access Input Data from AT Command Port

The source code of AT command set is not open-source, and is provided in the form of library file . It is also the basis to parse user-defined AT commands.

Define AT Commands

Before defining any AT command, you should first decide on the name and type of the AT command you want to define.

Naming rules:

• AT command should start with the + character.
• Alphabetic characters (A~Z, a~z), numeric characters (0~9), and some other characters (!, %, -, ., /, :, _) are supported. See AT Command Types for more information.

Command types:

Each AT command can have up to four types: Test Command, Query Command, Set Command, and Execute Command. See AT Command Types for more information.

Then, define each type of command. Assuming that AT+TEST supports all the four types. Below is the sample code to define each type.

Test Command:

uint8_t at_test_cmd_test(uint8_t *cmd_name)
{
    uint8_t buffer[64] = {0};

    snprintf((char *)buffer, 64, "this cmd is test cmd: %s\r\n", cmd_name);

    esp_at_port_write_data(buffer, strlen((char *)buffer));

    return ESP_AT_RESULT_CODE_OK;
}

Query Command:

uint8_t at_query_cmd_test(uint8_t *cmd_name)
{
    uint8_t buffer[64] = {0};

    snprintf((char *)buffer, 64, "this cmd is query cmd: %s\r\n", cmd_name);

    esp_at_port_write_data(buffer, strlen((char *)buffer));

    return ESP_AT_RESULT_CODE_OK;
}

Set Command:

uint8_t at_setup_cmd_test(uint8_t para_num)
{
    int32_t para_int_1 = 0;
    uint8_t *para_str_2 = NULL;
    uint8_t num_index = 0;
    uint8_t buffer[64] = {0};

    if (esp_at_get_para_as_digit(num_index++, &para_int_1) != ESP_AT_PARA_PARSE_RESULT_OK) {
        return ESP_AT_RESULT_CODE_ERROR;
    }

    if (esp_at_get_para_as_str(num_index++, &para_str_2) != ESP_AT_PARA_PARSE_RESULT_OK) {
        return ESP_AT_RESULT_CODE_ERROR;
    }

    snprintf((char *)buffer, 64, "this cmd is setup cmd and cmd num is: %u\r\n", para_num);
    esp_at_port_write_data(buffer, strlen((char *)buffer));

    memset(buffer, 0, 64);
    snprintf((char *)buffer, 64, "first parameter is: %d\r\n", para_int_1);
    esp_at_port_write_data(buffer, strlen((char *)buffer));

    memset(buffer, 0, 64);
    snprintf((char *)buffer, 64, "second parameter is: %s\r\n", para_str_2);
    esp_at_port_write_data(buffer, strlen((char *)buffer));

    return ESP_AT_RESULT_CODE_OK;
}

Execute Command:

uint8_t at_exe_cmd_test(uint8_t *cmd_name)
{
    uint8_t buffer[64] = {0};

    snprintf((char *)buffer, 64, "this cmd is execute cmd: %s\r\n", cmd_name);

    esp_at_port_write_data(buffer, strlen((char *)buffer));

    return ESP_AT_RESULT_CODE_OK;
}

Finally, call esp_at_cmd_struct to define the name and type(s) that your AT command supports. The sample code below defined the name +TEST (omitting AT) and all the four types.

static esp_at_cmd_struct at_custom_cmd[] = {
    {"+TEST", at_test_cmd_test, at_query_cmd_test, at_setup_cmd_test, at_exe_cmd_test},
};

If you do not want to define a particular type, set it to NULL.

Register AT Commands

Call API esp_at_custom_cmd_array_regist() to register your AT command. Below is the sample code to register AT+TEST:

esp_at_custom_cmd_array_regist(at_custom_cmd, sizeof(at_custom_cmd) / sizeof(at_custom_cmd[0]));

Note

esp_at_custom_cmd_array_regist is recommended to be added to the at_custom_init() in app_main().

Give it a try

If you have finished the above two steps, the command should work after you build the esp-at project and flash the firmware to your device. Give it a try!

Below is how AT+TEST works out.

Test Command:

AT+TEST=?

Response:

AT+TEST=?
this cmd is test cmd: +TEST

OK

Query Command:

AT+TEST?

Response:

AT+TEST?
this cmd is query cmd: +TEST

OK

Set Command:

AT+TEST=1,"espressif"

Response:

AT+TEST=1,"espressif"
this cmd is setup cmd and cmd num is: 2
first parameter is: 1
second parameter is: espressif

OK

Execute Command:

AT+TEST

Response:

AT+TEST
this cmd is execute cmd: +TEST

OK

Define Return Values

ESP-AT has defined return values in esp_at_result_code_string_index. See AT Messages for more return values.

In addition to output return values through the return mode, you can also use API esp_at_response_result() to output the execution result of the command. ESP_AT_RESULT_CODE_SEND_OK and ESP_AT_RESULT_CODE_SEND_FAIL can be used with the API in code.

For example, when you send data to the server or MCU with the Execute Command of AT+TEST, you can use esp_at_response_result to output the sending result, and the return mode to output the command execution result. Below is the sample code:

uint8_t at_exe_cmd_test(uint8_t *cmd_name)
{
    uint8_t buffer[64] = {0};

    snprintf((char *)buffer, 64, "this cmd is execute cmd: %s\r\n", cmd_name);

    esp_at_port_write_data(buffer, strlen((char *)buffer));

    // user-defined operation of sending data to server or MCU
    send_data_to_server();

    // output SEND OK
    esp_at_response_result(ESP_AT_RESULT_CODE_SEND_OK);

    return ESP_AT_RESULT_CODE_OK;
}

How it works out:

AT+TEST
this cmd is execute cmd: +TEST

SEND OK

OK

Access Command Parameters

ESP-AT provides two APIs to access command parameters:

• esp_at_get_para_as_digit() obtains digital parameters.
• esp_at_get_para_as_str() obtains string parameters.

See Set Command for an example.

Omit Command Parameters

This section describes how to provide optional command parameters:

• Omit the First or Middle Parameter
• Omit the Last Parameter

Omit the First or Middle Parameter

Let’s say you want to make <param_2> and <param_3> of AT+TEST optional. <param_2> is a digital parameter, and <param_3> a string parameter.

AT+TEST=<param_1>[,<param_2>][,<param_3>],<param_4>

Below is the sample code to achieve it:

uint8_t at_setup_cmd_test(uint8_t para_num)
{
    int32_t para_int_1 = 0;
    int32_t para_int_2 = 0;
    uint8_t *para_str_3 = NULL;
    uint8_t *para_str_4 = NULL;
    uint8_t num_index = 0;
    uint8_t buffer[64] = {0};
    esp_at_para_parse_result_type parse_result = ESP_AT_PARA_PARSE_RESULT_OK;

    snprintf((char *)buffer, 64, "this cmd is setup cmd and cmd num is: %u\r\n", para_num);
    esp_at_port_write_data(buffer, strlen((char *)buffer));

    parse_result = esp_at_get_para_as_digit(num_index++, &para_int_1);
    if (parse_result != ESP_AT_PARA_PARSE_RESULT_OK) {
        return ESP_AT_RESULT_CODE_ERROR;
    } else {
        memset(buffer, 0, 64);
        snprintf((char *)buffer, 64, "first parameter is: %d\r\n", para_int_1);
        esp_at_port_write_data(buffer, strlen((char *)buffer));
    }

    parse_result = esp_at_get_para_as_digit(num_index++, &para_int_2);
    if (parse_result != ESP_AT_PARA_PARSE_RESULT_OMITTED) {
        if (parse_result != ESP_AT_PARA_PARSE_RESULT_OK) {
            return ESP_AT_RESULT_CODE_ERROR;
        } else {
            // sample code
            // user needs to customize the operation
            memset(buffer, 0, 64);
            snprintf((char *)buffer, 64, "second parameter is: %d\r\n", para_int_2);
            esp_at_port_write_data(buffer, strlen((char *)buffer));
        }
    } else {
        // sample code
        // the second parameter is omitted
        // user needs to customize the operation
        memset(buffer, 0, 64);
        snprintf((char *)buffer, 64, "second parameter is omitted\r\n");
        esp_at_port_write_data(buffer, strlen((char *)buffer));
    }

    parse_result = esp_at_get_para_as_str(num_index++, &para_str_3);
    if (parse_result != ESP_AT_PARA_PARSE_RESULT_OMITTED) {
        if (parse_result != ESP_AT_PARA_PARSE_RESULT_OK) {
            return ESP_AT_RESULT_CODE_ERROR;
        } else {
            // sample code
            // user needs to customize the operation
            memset(buffer, 0, 64);
            snprintf((char *)buffer, 64, "third parameter is: %s\r\n", para_str_3);
            esp_at_port_write_data(buffer, strlen((char *)buffer));
        }
    } else {
        // sample code
        // the third parameter is omitted
        // user needs to customize the operation
        memset(buffer, 0, 64);
        snprintf((char *)buffer, 64, "third parameter is omitted\r\n");
        esp_at_port_write_data(buffer, strlen((char *)buffer));
    }

    parse_result = esp_at_get_para_as_str(num_index++, &para_str_4);
    if (parse_result != ESP_AT_PARA_PARSE_RESULT_OK) {
        return ESP_AT_RESULT_CODE_ERROR;
    } else {
        memset(buffer, 0, 64);
        snprintf((char *)buffer, 64, "fourth parameter is: %s\r\n", para_str_4);
        esp_at_port_write_data(buffer, strlen((char *)buffer));
    }

    return ESP_AT_RESULT_CODE_OK;
}

Note

If the string parameter input is "", it is not omitted.

Omit the Last Parameter

Let’s say you want to make the string parameter <param_3> optional, which is also the last parameter.

AT+TEST=<param_1>,<param_2>[,<param_3>]

There are two cases of omission:

• AT+TEST=<param_1>,<param_2>
• AT+TEST=<param_1>,<param_2>,

Below is the sample code to achieve it:

uint8_t at_setup_cmd_test(uint8_t para_num)
{
    int32_t para_int_1 = 0;
    uint8_t *para_str_2 = NULL;
    uint8_t *para_str_3 = NULL;
    uint8_t num_index = 0;
    uint8_t buffer[64] = {0};
    esp_at_para_parse_result_type parse_result = ESP_AT_PARA_PARSE_RESULT_OK;

    snprintf((char *)buffer, 64, "this cmd is setup cmd and cmd num is: %u\r\n", para_num);
    esp_at_port_write_data(buffer, strlen((char *)buffer));

    parse_result = esp_at_get_para_as_digit(num_index++, &para_int_1);
    if (parse_result != ESP_AT_PARA_PARSE_RESULT_OK) {
        return ESP_AT_RESULT_CODE_ERROR;
    } else {
        memset(buffer, 0, 64);
        snprintf((char *)buffer, 64, "first parameter is: %d\r\n", para_int_1);
        esp_at_port_write_data(buffer, strlen((char *)buffer));
    }

    parse_result = esp_at_get_para_as_str(num_index++, &para_str_2);
    if (parse_result != ESP_AT_PARA_PARSE_RESULT_OK) {
        return ESP_AT_RESULT_CODE_ERROR;
    } else {
        memset(buffer, 0, 64);
        snprintf((char *)buffer, 64, "second parameter is: %s\r\n", para_str_2);
        esp_at_port_write_data(buffer, strlen((char *)buffer));
    }

    if (num_index == para_num) {
        memset(buffer, 0, 64);
        snprintf((char *)buffer, 64, "third parameter is omitted\r\n");
        esp_at_port_write_data(buffer, strlen((char *)buffer));
    } else {
        parse_result = esp_at_get_para_as_str(num_index++, &para_str_3);
        if (parse_result != ESP_AT_PARA_PARSE_RESULT_OMITTED) {
            if (parse_result != ESP_AT_PARA_PARSE_RESULT_OK) {
                return ESP_AT_RESULT_CODE_ERROR;
            } else {
                // sample code
                // user needs to customize the operation
                memset(buffer, 0, 64);
                snprintf((char *)buffer, 64, "third parameter is: %s\r\n", para_str_3);
                esp_at_port_write_data(buffer, strlen((char *)buffer));
            }
        } else {
            // sample code
            // the third parameter is omitted
            // user needs to customize the operation
            memset(buffer, 0, 64);
            snprintf((char *)buffer, 64, "third parameter is omitted\r\n");
            esp_at_port_write_data(buffer, strlen((char *)buffer));
        }
    }

    return ESP_AT_RESULT_CODE_OK;
}

Note

If the string parameter input is "", it is not omitted.

Block Command Execution

Sometimes you want to block the execution of one command to wait for another execution result, and the system may return different values according to the result.

Generally, this kind of command needs to synchronize the results of other tasks.

semaphore is recommended to handle synchronization.

The sample code is as follows:

xSemaphoreHandle at_operation_sema = NULL;

uint8_t at_exe_cmd_test(uint8_t *cmd_name)
{
    uint8_t buffer[64] = {0};

    snprintf((char *)buffer, 64, "this cmd is execute cmd: %s\r\n", cmd_name);

    esp_at_port_write_data(buffer, strlen((char *)buffer));

    // sample code
    // users don't have to create semaphores here
    at_operation_sema = xSemaphoreCreateBinary();
    assert(at_operation_sema != NULL);

    // block command execution
    // wait for another execution result
    // other tasks can call xSemaphoreGive to release the semaphore
    xSemaphoreTake(at_operation_sema, portMAX_DELAY);

    return ESP_AT_RESULT_CODE_OK;
}

Access Input Data from AT Command Port

ESP-AT supports accessing input data from AT Command port. It provides two APIs for this purpose.

• esp_at_port_enter_specific() sets the callback function which will be called by AT port after receiving the input data.
• esp_at_port_exit_specific() deletes the callback function set by esp_at_port_enter_specific.

Approaches to access the data vary depending on whether the data length has been specified or not.

Input Data of Specified Length

Assuming that you have specified the data length in <param_1> as follows:

AT+TEST=<param_1>

Below is the sample to access the input data of <param_1> length from AT Command Port:

static xSemaphoreHandle at_sync_sema = NULL;

void wait_data_callback(void)
{
    xSemaphoreGive(at_sync_sema);
}

uint8_t at_setup_cmd_test(uint8_t para_num)
{
    int32_t specified_len = 0;
    int32_t received_len = 0;
    int32_t remain_len = 0;
    uint8_t *buf = NULL;
    uint8_t buffer[64] = {0};

    if (esp_at_get_para_as_digit(0, &specified_len) != ESP_AT_PARA_PARSE_RESULT_OK) {
        return ESP_AT_RESULT_CODE_ERROR;
    }

    buf = (uint8_t *)malloc(specified_len);
    if (buf == NULL) {
        memset(buffer, 0, 64);
        snprintf((char *)buffer, 64, "malloc failed\r\n");
        esp_at_port_write_data(buffer, strlen((char *)buffer));
    }

    // sample code
    // users don't have to create semaphores here
    if (!at_sync_sema) {
        at_sync_sema = xSemaphoreCreateBinary();
        assert(at_sync_sema != NULL);
    }

    // output input prompt ">"
    esp_at_port_write_data((uint8_t *)">", strlen(">"));

    // set the callback function which will be called by AT port after receiving the input data
    esp_at_port_enter_specific(wait_data_callback);

    // receie input data
    while(xSemaphoreTake(at_sync_sema, portMAX_DELAY)) {
        received_len += esp_at_port_read_data(buf + received_len, specified_len - received_len);

        if (specified_len == received_len) {
            esp_at_port_exit_specific();

            // get the length of the remaining input data
            remain_len = esp_at_port_get_data_length();
            if (remain_len > 0) {
                // sample code
                // if the remaining data length > 0, the actual input data length is greater than the specified received data length
                // users can customize the operation to process the remaining data
                // here is just a simple print out of the remaining data
                esp_at_port_recv_data_notify(remain_len, portMAX_DELAY);
            }

            // sample code
            // output received data
            memset(buffer, 0, 64);
            snprintf((char *)buffer, 64, "\r\nreceived data is: ");
            esp_at_port_write_data(buffer, strlen((char *)buffer));

            esp_at_port_write_data(buf, specified_len);

            break;
        }
    }

    free(buf);

    return ESP_AT_RESULT_CODE_OK;
}

So, if you set AT+TEST=5 and the input data is 1234567890, the ESP-AT output is as follows.

AT+TEST=5
>67890
received data is: 12345
OK

Input Data of Unspecified Length

This scenario is similar to the Wi-Fi Passthrough Mode. You do not specify the data length.

AT+TEST

Assuming that ESP-AT ends the execution of the command and returns the execution result, the sample code is as follows:

#define BUFFER_LEN (2048)
static xSemaphoreHandle at_sync_sema = NULL;

void wait_data_callback(void)
{
    xSemaphoreGive(at_sync_sema);
}

uint8_t at_exe_cmd_test(uint8_t *cmd_name)
{
    int32_t received_len = 0;
    int32_t remain_len = 0;
    uint8_t *buf = NULL;
    uint8_t buffer[64] = {0};


    buf = (uint8_t *)malloc(BUFFER_LEN);
    if (buf == NULL) {
        memset(buffer, 0, 64);
        snprintf((char *)buffer, 64, "malloc failed\r\n");
        esp_at_port_write_data(buffer, strlen((char *)buffer));
    }

    // sample code
    // users don't have to create semaphores here
    if (!at_sync_sema) {
        at_sync_sema = xSemaphoreCreateBinary();
        assert(at_sync_sema != NULL);
    }

    // output input prompt ">"
    esp_at_port_write_data((uint8_t *)">", strlen(">"));

    // set the callback function which will be called by AT port after receiving the input data
    esp_at_port_enter_specific(wait_data_callback);

    // receie input data
    while(xSemaphoreTake(at_sync_sema, portMAX_DELAY)) {
        memset(buf, 0, BUFFER_LEN);

        received_len = esp_at_port_read_data(buf, BUFFER_LEN);
        // check whether to exit the mode
        // the exit condition is the “+++” string received
        if ((received_len == 3) && (strncmp((const char *)buf, "+++", 3)) == 0) {
            esp_at_port_exit_specific();

            // sample code
            // if the remaining data length > 0, it means that there is still data left in the buffer to be processed
            // users can customize the operation to process the remaining data
            // here is just a simple print out of the remaining data
            remain_len = esp_at_port_get_data_length();
            if (remain_len > 0) {
                esp_at_port_recv_data_notify(remain_len, portMAX_DELAY);
            }

            break;
        } else if (received_len > 0) {
            // sample code
            // users can customize the operation to process the received data
            // here is just a simple print received data
            memset(buffer, 0, 64);
            snprintf((char *)buffer, 64, "\r\nreceived data is: ");
            esp_at_port_write_data(buffer, strlen((char *)buffer));

            esp_at_port_write_data(buf, strlen((char *)buf));
        }
    }

    free(buf);

    return ESP_AT_RESULT_CODE_OK;
}

So, if the first input data is 1234567890, and the second input data is +++, the ESP-AT output is as follows:

AT+TEST
>
received data is: 1234567890
OK

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