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I am writing device driver and i am completely new to this concept. My Driver functionality is when i connect modem to usb my driver should detect Connected modem and get display the signal strength. How can i do that using AT commands. Modem is CDMA modem. Help Me please

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In general the standard command to get the signal quality is AT+CSQ?

How you dialogue with your modem really depends on your specific modem. Usually the modem would be seen as a "normal" serial port if an internal usb to serial is present (so you would have something like /dev/ttyUSB0 or /dev/ttyUSBx) or eventually as a CDC device (so you would see a /dev/ttyACM0 or /dev/ttyACMx). You should open this serial device (with correct bauding and so on) and send the AT commands there and read the responses.

To know what (and even if) the modem device to use it I could suggest to do a "dmesg" after plugging the modem and you should hopefully see some messages pointing at the detected device.

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