AT FAQ

[中文]

AT Firmware

There is no released firmware for my module. Where can I get the firmware for it?

If there is no released fimware for your module in the AT Binary Lists chapter, please consider the following options:

How to get the source code of AT firmware?

The esp-at project is distributed as a combination of source code and pre-compiled libraries in this repository. The pre-compiled core libraries (under the directory: esp-at/components/at/lib/) are closed-source, and there is no plan for open-sourcing them.

How to download the AT firmware on Espressif’s official website?

How to combine all the bin files compiled by ESP-AT?

You can use the combine button of the Flash Download Tools.

Does the AT firmware shipped in modules support flow control?

AT Commands and Responses

What is the reason why AT prompts busy?

  • The “busy” prompt indicates that the previous command is being executed, and the system cannot respond to the current input. The processing mechanism of the AT commands is serial, i.e. one command at a time.

  • Any input through serial ports is considered to be a command input, so the system will also prompt “busy” or “ERROR” when there is any extra invisible character input.

    • Serial input AT+GMR (change character CR LF) (space character), because AT+GMR (change character CR LF) is already a complete AT command, the system will execute the command. At this time, if the system has not completed the AT+GMR operation, it has received the following space character, which will be regarded as a new command input, and the system will prompt “busy”. But if the system has completed the AT+GMR operation, and then receives the following space character, the space character will be regarded as an error command, and the system will prompt “ERROR”.

    • After the MCU sends AT+CIPSEND and receives the busy p.. response, the MCU needs to resend the data. Because busy p.. represents the previous command is being executed, the current input is invalid. It is recommended to wait for the response of the last AT command before the MCU sends a new command again.

Why does the ESP-AT firmware always return the following message after the I powered up the device and sent the first command?

ERR CODE:0x010b0000
busy p...

  • This message means that the previous command is being executed.

  • Normally only “busy p…” is displayed. The ERR CODE is displayed because the error code prompt is enabled.

  • If you receive this message after sending the first command on power-up, the possible reasons are: the command is followed by the unnecessary newline/space/other symbols; or two or more AT commands are sent in succession.

What commands are supported by the default ESP-AT firmware on different modules, and from which version are they supported?

  • To learn what commands are supported by the default ESP-AT firmware on different modules, please refer to ESP-AT Firmware Differences.

  • To learn from which version a command is supported and what issues are fixed in each version, please refer to release notes.

When the host MCU sends an AT command to the ESP32-C2 device, there is no response. What is the reason?

A terminator (“AT\r\n”) must be added after an AT command when the host MCU sending AT commands to an ESP32-C2 device. Please see Check Whether AT Works.

Why is Wi-Fi disconnected (WIFI DISCONNECT printed)?

You can check the Wi-Fi disconnection reason code on the AT log port, which usually prints wifi disconnected, rc:<reason_code>. The <reason_code> here refers to Wi-Fi Reason Code.

What are the common Wi-Fi compatibility issues?

  • AMPDU compatibility issue.

    • If the router does not support AMPDU, ESP32-C2 will automatically disable the AMPDU function when interacting with the router.

    • If the router supports AMPDU but there is a compatibility issue with AMPDU transmission between the router and ESP32-C2, it is recommended to disable the function on the router or ESP32-C2. For information on how to disable it on ESP32-C2, please refer to Compile ESP-AT Project Locally and select the following options in the fifth step of configuring the project:

      • Disable Component config -> Wi-Fi -> WiFi AMPDU TX

      • Disable Component config -> Wi-Fi -> WiFi AMPDU RX

  • Phy mode compatibility issue. If there is a compatibility issue with the phy mode between the router and ESP32-C2, it is recommended to switch it on the router or ESP32-C2. For how to switch it on ESP32-C2, please refer to the AT+CWSTAPROTO command.

Do AT commands support ESP-WIFI-MESH?

Currently, AT commands do not support ESP-WIFI-MESH.

Can AT command set Bluetooth LE transmit power?

Yes, the AT+RFPOWER command can set Bluetooth LE transmit power. ESP32-C2 Wi-Fi and Bluetooth LE share the same antenna.

How to support commands that are not supported by the default firmware but can be supported after configuring and compiling the ESP-AT project?

For example, if you need to support the WPA2 Enterprise function on the ESP32-C2 series, configure and compile the firmware by yourself. Open the WPA2 Enterprise function in menuconfig when compiling: ./build.py menuconfig > Component config > AT > [*]AT WPA2 Enterprise command support.

How to handle special characters in AT commands?

Please refer to the escape character syntax described in the AT Command Types section.

Can the serial port baudrate be modified in AT Commands? (Default: 115200)

Yes, you can use either of the two ways below to modify it:

After ESP32-C2 enters the passthrough mode using AT commands, can ESP32-C2 give a message if the connected hotspot is disconnected?

  • Yes, you can configure it with AT+SYSMSG, i.e., set AT+SYSMSG=4. In this way, the serial port will report WIFI DISCONNECT\\r\\n when the connected hotspot is disconnected.

  • Note that this command is added after AT v2.1.0. It is not available for v2.1.0 and earlier versions.

How to enable the notify and indicate functions on Bluetooth LE clients?

  • Besides the read and write properties, Bluetooth LE characteristics also have the notify and indicate properties, which allow the server to send data to the client, but the client must first register for notification by writing the value of “CCCD”.

  • To enable notify, write 0x01. To enable indicate, write 0x02 (for the descriptor “0x2902”). To enable both notify and indicate, write 0x03.

  • The example below demonstrates how to enable the notify and indicate properties for the descriptor 0x2902 under the services 0xC305 and 0xC306 respectively. The two services are default services in ESP-AT, of which 0xC305 can be notified and 0xC306 can be indicated.

AT+BLEGATTCWR=0,3,6,1,2
>
// Write low byte 0x01 high byte 0x00 (if you want to use hex format, it is: 0100)
OK
// Server: +WRITE:0,1,6,1,2,<0x01>,<0x00>
AT+BLEGATTCWR=0,3,7,1,2
>
// Write low byte 0x02 high byte 0x00 (if you want to use hex format, it is: 0200)
OK
// Server: +WRITE:0,1,6,1,2,<0x02>,<0x00>
// Writing ccc is a prerequisite for the server to be able to send notify and indicate

Hardware

How big is the chip flash required for ESP-AT firmware on different modules?

How to view the error log of AT firmware?

  • For ESP32-C2, the error log is output through the download port. By default, UART0 is GPIO21 and GPIO20.

  • See Hardware Connection for more details.

The UART1 communication pin used by ESP-AT on the ESP32-C2 module is inconsistent with the default UART1 pin described in the ESP32-C2 module’s datasheet?

  • ESP32-C2 supports IO matrix. When compiling ESP-AT, you can configure UART1 pins in menuconfig, so they may be inconsistent with the pins described in the module datasheet.

  • See factory_param_data.csv for more details.

Performance

How long does it take for the AT to connect to Wi-Fi?

  • In an office scenario, the connection time is 5 seconds. However, in actual practice, Wi-Fi connection time depends on the router performance, network environment, module antenna performance, etc.

  • The maximum timeout time can be set by the <jap_timeout> parameter of AT+CWJAP.

Is it possible to change the TCP send window size in AT firmware?

  • Currently, it cannot be changed by AT commands, but you can configure and compile the ESP-AT project to generate a new firmware.

  • You can configure the menuconfig parameter: Component config > LWIP > TCP > Default send buffer size.

How to test and optimize the throughput of ESP32-C2 AT?

  • Many factors are affecting the AT throughput test. It is recommended to use the iperf example in esp-idf for testing. While testing, please use the passthrough mode, adjust the data length to 1460 bytes, and send data continuously.

  • If the test rate does not meet your requirements, please refer to How to Improve ESP-AT Throughput Performance.

How to modify the default maximum number of TCP segment retransmissions for ESP32-C2 AT?

By default, the maximum number of TCP segment retransmissions for AT is 6. You can reconfigure the maximum number of TCP segment retransmissions (range: [3-12]) as follows:

Other

What interfaces of ESP32-C2 chips can be used to transmit AT commands?

  • ESP32-C2 can transmit AT commands through UART and SPI.

  • The default firmware uses UART for transmission. If you need SDIO or SPI interface to transmit AT commands, you can configure it through ./build.py menuconfig > Component config > AT when compiling the ESP-AT project by yourself.

  • See AT through SDIO , AT through SPI , or AT through socket for more details.

How does ESP-AT conduct BQB certification?

Please contact Espressif for solutions.

How do I specify the TLS protocol version for ESP32-C2 AT?

When compiling the esp-at project, you can disable the unwanted versions in the ./build.py menuconfig > Component config > mbedTLS.

How to modify the number of TCP connections in AT?

  • At present, the maximum number of TCP connections of the AT default firmware is 5.

  • The ESP32-C2 AT supports a maximum of 16 TCP connections, which can be configured in menuconfig as follows:

    • ./build.py menuconfig > Component config > AT > (16)AT socket maximum connection number

    • ./build.py menuconfig > LWIP > (16)Max number of open sockets

Does ESP32-C2 AT support PPP?

  • Not supported, please refer to pppos_client demos for your own implementation.

How to enable debug log for AT?

  • Enable log level: ./build.py menuconfig > Component Config > Log output > Default log verbosity set to Debug.

    • Enable Wi-Fi debug: ./build.py menuconfig > Component config > Wi-Fi > Wi-Fi debug log level set to Debug.

    • Enable TCP/IP debug: ./build.py menuconfig > Component config > LWIP > Enable LWIP Debug > Set the log level of the specific part you want to debug to Debug.

    • Enable Bluetooth LE debug: ./build.py menuconfig > Component config > Bluetooth > Bluedroid Options > Disable BT debug logs > BT DEBUG LOG LEVEL > Set the log level of the specific part you want to debug to Debug.

How does the AT command implement the functionality of resuming HTTP transfers after interrupts?

  • Currently, AT commands provide two methods:

    • Specify the data range to be read using the HTTP Range field. For specific details, please refer to the example of AT+HTTPCHEAD.

    • You can construct an HTTP GET request using AT TCP series commands. Between steps 6 and 7 of the example ESP32-C2 obtains socket data in passive receiving mode, add a step: Use the AT+CIPSEND command to send your own HTTP GET request header to the server. In passive receive mode, for HTTP GET request data received from the server, the MCU needs to actively send the AT+CIPRECVDATA command to read the data. This helps avoid situations where the MCU may be unable to process data promptly due to large amounts of data being transferred from the server.

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