如何使用picocom获取AT命令响应？OpenWrt下EM7455脚本改造需求

我在搭载OpenWrt 22.03.5固件的路由器上使用EM7455调制解调器，原本用atinout编写了控制脚本，但atinout（包括echo+cat、socat）经常发送错误命令，比如截断命令、出现乱码。只有通过picocom手动执行命令时能正常工作，因此想改用picocom重写脚本。

原atinout脚本 #

#!/bin/sh
modemPort=$(ls /dev/ttyUSB* | tail -n 1)
echo "$modemPort" | grep -E -o -q -i "ttyUSB" || exit 0

status=$(echo "at!gstatus?" | atinout - $modemPort -)
hexGoodBS="08199120"

if echo "$status" | grep -E -o -q -i "Normal Service"; then
    if ! echo "$status" | grep -E -o -q -i "Cell ID:\s*$hexGoodBS\s*\(\d+\)"; then
        echo "at!band=09" | atinout - $modemPort -
    fi
elif echo "$status" | grep -E -o -q -i "Attach Needed"; then
    if echo "at!band?" | atinout - $modemPort - | grep -E -o -q -i "Band_3"; then
        if echo "$status" | grep -E -o -q -i "Cell ID:\s*$hexGoodBS\s*\(\d+\)"; then
            echo "at!band=09" | atinout - $modemPort -
            sleep 3
            echo "at!band=03" | atinout - $modemPort -
        else
            echo "at!band=09" | atinout - $modemPort -
        fi
    fi
elif echo "$status" | grep -E -o -q -i "(No (Cell|band)|PLMN Search)"; then
    if ! echo "at!band?" | atinout - $modemPort - | grep -E -o -q -i "LTE ALL"; then
        echo "at!band=09" | atinout - $modemPort - #LTE ALL
    fi
fi

ifup EM7455

命令发送错误示例 #

root@Xiaomi-Mi-Router-3G:~# echo at!gstatus? | atinout - /dev/ttyUSB2 -
at!b


ERROR
root@Xiaomi-Mi-Router-3G:~# echo at!gstatus? | atinout - /dev/ttyUSB2 -


ERROR
root@Xiaomi-Mi-Router-3G:~# echo at!gstatus? | atinout - /dev/ttyUSB2 -
at!gstatus?


!GSTATUS:

Current Time:  26655            Temperature: 33

Reset Counter: 1                Mode:        ONLINE

System mode:   LTE              PS state:    Not attached

LTE band:      No band          LTE bw:      1.4 MHz

LTE Rx chan:   0                LTE Tx chan: 4294967295

LTE CA state:  NOT ASSIGNED

EMM state:     Deregistered     Attach Needed

RRC state:     RRC Idle

IMS reg state: No Srv



PCC RxM RSSI:  0                RSRP (dBm):  0

PCC RxD RSSI:  0                RSRP (dBm):  0

Tx Power:      --               TAC:         FFFF (65535)

RSRQ (dB):     0.0              Cell ID:     FFFFFFFF (4294967295)

SINR (dB):




OK
root@Xiaomi-Mi-Router-3G:~# echo at!gstatus? | atinout - /dev/ttyUSB2 -


ERROR
root@Xiaomi-Mi-Router-3G:~# echo at!gstatus? | atinout - /dev/ttyUSB2 -
at!gren E cttacIrFat!gstatus?


ERROR
root@Xiaomi-Mi-Router-3G:~#

临时解决方案 #

发送AT命令前执行：stty -F /dev/ttyUSB2 raw -echo

重写后的picocom脚本 #

#!/bin/sh
modemPort=$(ls /dev/ttyUSB* | tail -n 1)
echo "$modemPort" | grep -E -o -q -i "ttyUSB" || exit 0

# 封装picocom发送AT命令的函数，过滤无关输出
send_at_cmd() {
    local cmd="$1"
    # 波特率115200为EM7455默认值，可根据实际调整；-t 2设置2秒超时
    echo -e "$cmd\r" | picocom -b 115200 -t 2 "$modemPort" 2>/dev/null | grep -vE "(picocom|Terminal ready|exit|^$)"
}

hexGoodBS="08199120"
status=$(send_at_cmd "at!gstatus?")

if echo "$status" | grep -E -o -q -i "Normal Service"; then
    if ! echo "$status" | grep -E -o -q -i "Cell ID:\s*$hexGoodBS\s*\(\d+\)"; then
        send_at_cmd "at!band=09"
    fi
elif echo "$status" | grep -E -o -q -i "Attach Needed"; then
    band_status=$(send_at_cmd "at!band?")
    if echo "$band_status" | grep -E -o -q -i "Band_3"; then
        if echo "$status" | grep -E -o -q -i "Cell ID:\s*$hexGoodBS\s*\(\d+\)"; then
            send_at_cmd "at!band=09"
            sleep 3
            send_at_cmd "at!band=03"
        else
            send_at_cmd "at!band=09"
        fi
    fi
elif echo "$status" | grep -E -o -q -i "(No (Cell|band)|PLMN Search)"; then
    band_status=$(send_at_cmd "at!band?")
    if ! echo "$band_status" | grep -E -o -q -i "LTE ALL"; then
        send_at_cmd "at!band=09" #LTE ALL
    fi
fi

ifup EM7455

脚本说明 #

• 新增send_at_cmd函数，统一处理AT命令的发送与结果过滤，避免picocom自身输出干扰
• 设置2秒超时时间，防止脚本无限等待
• 屏蔽picocom的错误输出，只保留调制解调器返回的有效内容

内容的提问来源于stack exchange，提问作者vars-cat