sim-modem/api/modem/utils/signal.go

package utils

import (
	"fmt"
	"log"
	"strconv"
	"strings"

	"gitea.unprism.ru/KRBL/sim-modem/api/modem/at"
)

func CheckSignal(port at.Port, logger *log.Logger) (bool, error) {
	rssi, ber, err := getSignalQuality(port)
	if err != nil {
		return false, fmt.Errorf("get signal quality: %w", err)
	}
	logger.Printf("check signal: rssi=%d ber=%d\n", rssi, ber)
	if err := checkRssi(rssi); err != nil {
		return false, nil
	}
	if err := checkBer(ber); err != nil {
		logger.Printf("bad ber(not critical): %s", err.Error()) // Happened not to be critical
	}
	return true, nil
}

func checkRssi(rssi int) error {
	// rssi - Received signal strenght indicator
	// 0          -113 dBm or less
	// 1          -111 dBm
	// 2...30     -109... - 53 dBm
	// 31         -51 dBm or greater
	// 99         not known or not detectable
	// 100        -116 dBm or less
	// 101        -115 dBm
	// 102…191    -114... - 26dBm
	// 191        -25 dBm or greater
	// 199        not known or not detectable
	// 100…199    expand to TDSCDMA, indicate RSCPreceived

	if rssi <= 2 { // Too poor
		return fmt.Errorf("too poor <= -109dBm")
	}
	if rssi > 2 && rssi <= 31 {
		return nil // Can live
	}
	if rssi == 99 {
		return fmt.Errorf("not known or not detectable")
	}
	if rssi >= 100 && rssi <= 102 {
		return fmt.Errorf("too poor <= -114dBm")
	}
	if rssi > 102 && rssi <= 191 {
		return nil // Can live
	}
	if rssi == 199 {
		return fmt.Errorf("not known or not detectable")
	}
	return fmt.Errorf("invalid code %d", rssi)
}

func checkBer(ber int) error {
	// ber - Bit error rate
	// 0       <0.01%
	// 1       0.01% --- 0.1%
	// 2       0.1% --- 0.5%
	// 3       0.5% --- 1.0%
	// 4       1.0% --- 2.0%
	// 5       2.0% --- 4.0%
	// 6       4.0% --- 8.0%
	// 7       >=8.0%
	// 99      not known or not detectable
	if ber >= 0 && ber <= 3 {
		// ber -> [0%;1%)
		// Ok, can live
		return nil
	}
	if ber >= 4 && ber <= 7 {
		return fmt.Errorf("too high: %d code", ber)
	}
	if ber == 99 {
		return fmt.Errorf("not known or not detectable")
	}
	return fmt.Errorf("invalid code %d", ber)
}

// Returns rssi and ber(look above)
func getSignalQuality(port at.Port) (int, int, error) {
	resp, err := port.Send("AT+CSQ")
	if err != nil {
		return 99, 99, err
	}
	if !resp.Check() || !resp.CheckFront("+CSQ: ") {
		return 99, 99, fmt.Errorf("error response: %s", resp)
	}
	values := strings.Split(strings.ReplaceAll(strings.Split(resp.RmFront("+CSQ: ").String(), "\n")[0], "\r", ""), ",")
	if len(values) != 2 {
		return 99, 99, fmt.Errorf("invalid values(len): [% s]", values)
	}
	rssi, err := strconv.Atoi(values[0])
	if err != nil {
		return 99, 99, fmt.Errorf("parse rssi: %w", err)
	}
	ber, err := strconv.Atoi(values[1])
	if err != nil {
		return 99, 99, fmt.Errorf("parse ber: %w", err)
	}
	return rssi, ber, nil
}