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RPCD AT Daemon User Guide

Why Use This Service

  1. Queue Mechanism: This service implements a command queue to ensure that only one AT command runs at a time, avoiding concurrent errors in the modem's ATD service
  2. Multiple Invocation Methods: The service can be called by other services on the router via ubus, or by HTTP services via rpcd, making it suitable for both modem management and WebUI development
  3. Better Stability: Compared to the modem's built-in ATD service, this service provides more stable and reliable performance across different vendor modems

Usage Instructions

1. Configure rpcd Permissions

Add rpcd permissions for at-daemon (for demonstration purposes, the following configuration is unauthenticated - please configure appropriate authentication for production environments)

echo << EOF > /usr/share/rpcd/acl.d/unauthenticated.json
{
        "unauthenticated": {
                "description": "Access controls for unauthenticated requests",
                "read": {
                        "ubus": {
                                "session": [
                                        "access",
                                        "login"
                                ],
                                "at-daemon" : ["list","open","sendat","close"]
                        }
                }
        }
}
EOF

2. Send AT Commands via HTTP Interface

Use curl to access rpcd and send commands:

curl -s -X POST -H "Content-Type: application/json" -d '
{
    "jsonrpc":"2.0",
    "id":1,
    "method":"call",
    "params":["00000000000000000000000000000000","at-daemon","sendat",{"at_port":"/dev/ttyUSB0","at_cmd":"at+cgmm"}]
}
' http://192.168.1.1/ubus

Response example:

{
   "jsonrpc": "2.0",
   "id": 1,
   "result": [
     0,
     {
       "port": "/dev/ttyUSB0",
       "command": "at+cgmm",
       "is_raw": 0,
       "sendonly": 0,
       "timeout": 5,
       "end_flag": "default",
       "end_flags_used": [
         "OK",
         "ERROR",
         "+CMS ERROR:",
         "+CME ERROR:",
         "NO CARRIER"
       ],
       "status": "success",
       "response": "\r\nMH5000-82M\r\n\r\nOK\r\n",
       "response_length": 20,
       "end_flag_matched": "OK",
       "response_time_ms": 79
     }
   ]
 }

3. Send AT Commands via ubus

You can also use ubus commands directly on the router:

ubus call at-daemon sendat '{"at_port":"/dev/ttyUSB0","at_cmd":"at+cgmm"}'

API Reference

ubus -v list at-daemon
'at-daemon' @de5d6d53
        "open":{"at_port":"String","baudrate":"Integer","databits":"Integer","parity":"Integer","stopbits":"Integer","timeout":"Integer"}
        "sendat":{"at_port":"String","timeout":"Integer","end_flag":"String","at_cmd":"String","raw_at_content":"String","sendonly":"Boolean"}
        "list":{}
        "close":{"at_port":"String"}

Method Descriptions

open - Open Serial Port

Opens the specified serial port device (usually called automatically when using sendat)

Parameters:

  • at_port (String, required): Serial port device path, e.g., /dev/ttyUSB0
  • baudrate (Integer, optional): Baud rate, default 115200
  • databits (Integer, optional): Data bits, default 8
  • parity (Integer, optional): Parity bit, 0=none, 1=odd, 2=even
  • stopbits (Integer, optional): Stop bits, 1 or 2
  • timeout (Integer, optional): Timeout in seconds, default 5

sendat - Send AT Command

Sends an AT command to the specified serial port and receives the response

Parameters:

  • at_port (String, required): Serial port device path
  • at_cmd (String, optional): AT command content, e.g., at+cgmm
  • raw_at_content (String, optional): Raw content in hexadecimal format, choose one between this and at_cmd
  • timeout (Integer, optional): Timeout in seconds, default 5
  • sendonly (Boolean, optional): Whether to send only without receiving response, default false
  • end_flag (String, optional): Custom termination character, truncates when this character is detected in response

Default Termination Characters: OK, ERROR, +CMS ERROR:, +CME ERROR:, NO CARRIER

list - List Serial Ports

Lists all opened serial port connections

Parameters: None

close - Close Serial Port

Closes the specified serial port connection

Parameters:

  • at_port (String, required): Serial port device path to close

Important Notes

1. Sharing Serial Port with QModem

If you want to share the serial port with QModem, you need to enable ubus at mode in QModem configuration. Otherwise, ubus at will monopolize the serial port buffer after startup, preventing QModem from receiving information.

Configuration method:

uci set qmodem.1_1_2.use_ubus='1'
uci commit qmodem

2. Response Termination Characters

When calling ubus-at-daemon in your project, ensure that AT commands return one of the following termination characters:

  • OK
  • ERROR
  • +CMS ERROR:
  • +CME ERROR:
  • NO CARRIER

Or manually specify a termination character via the end_flag parameter. Otherwise, the request will wait until timeout and status will return an error.

3. Security Recommendation

Unauthenticated rpcd configuration is not recommended for production environments. Please configure appropriate authentication mechanisms based on your security requirements.

Usage Examples

Query Modem Model

ubus call at-daemon sendat '{"at_port":"/dev/ttyUSB0","at_cmd":"at+cgmm"}'

Query Signal Strength

ubus call at-daemon sendat '{"at_port":"/dev/ttyUSB0","at_cmd":"at+csq"}'

Send Command Without Waiting for Response

ubus call at-daemon sendat '{"at_port":"/dev/ttyUSB0","at_cmd":"at+cfun=1,1","sendonly":true}'

Custom Timeout

ubus call at-daemon sendat '{"at_port":"/dev/ttyUSB0","at_cmd":"at+cgmm","timeout":10}'