AT+CESQ signal strength 255 (unknown) yet connection works great

[GJSea]

Hi,

In order to determine signal strength we parse the AT+CESQ response and regularly get +CESQ: 99,99,255,255,255,255 (the final number being the strength), but the connection and connectivity is perfectly fine. Is there a reason 255 is returned for the strength even though all connectivity is good?

Thanks! 

[Carl Richard]

Hi, GJSea!

Are you using Power Saving Mode(PSM) in your project? While the device is in PSM the radio is off and the device is disconnected. 

I have not seen a similar behavior in any other cases, so I must reach out to the modem team if the above is not the case.

Best regards,
Carl Richard

[duxinglang]

Now, I also encountered this problem, when I started my project, I used the AT command to query CESQ, it returned was 255. However, when i call the sample code for MQTT and find that it can connect to an LTE network, and even more bizarrely, on my other PCBA board, I write the same firmware and CESQ returns the correct values, which is very strange!

I confirm that I did not control the modem to enter PSM mode. This is my prj.conf file:

#
# Copyright (c) 2019 Nordic Semiconductor ASA
#
# SPDX-License-Identifier: LicenseRef-BSD-5-Clause-Nordic
#
# General config
CONFIG_NEWLIB_LIBC=y
CONFIG_NEWLIB_LIBC_FLOAT_PRINTF=y
CONFIG_ASSERT=y
CONFIG_REBOOT=y
CONFIG_GPIO=y
CONFIG_TRUSTED_EXECUTION_NONSECURE=y

# Log
CONFIG_LOG=y
CONFIG_LOG_IMMEDIATE=y
CONFIG_USE_SEGGER_RTT=y
CONFIG_LOG_BACKEND_RTT=y
CONFIG_LOG_BACKEND_UART=n
CONFIG_LOG_DEFAULT_LEVEL=4
CONFIG_LOG_MODE_OVERFLOW=y
CONFIG_LOG_BACKEND_RTT_MODE_DROP=y
CONFIG_LOG_BACKEND_SHOW_COLOR=n
CONFIG_LOG_BACKEND_FORMAT_TIMESTAMP=n

# Modem info
CONFIG_MODEM_INFO=y

# BSD library
CONFIG_BSD_LIBRARY=y
CONFIG_BSD_LIBRARY_TRACE_ENABLED=n

# Flash
CONFIG_FLASH=y
CONFIG_IMG_ERASE_PROGRESSIVELY=y

# NVS
CONFIG_FLASH=y
CONFIG_FLASH_PAGE_LAYOUT=y
CONFIG_NVS=y
CONFIG_NVS_LOG_LEVEL_DBG=y
CONFIG_MPU_ALLOW_FLASH_WRITE=y

# GPS
CONFIG_AT_CMD=y
CONFIG_AT_NOTIF=y

# AT_CMD
CONFIG_AT_HOST_LIBRARY=y
CONFIG_UART_INTERRUPT_DRIVEN=y

# Console
CONFIG_CONSOLE_SUBSYS=n
CONFIG_CONSOLE_HANDLER=n
CONFIG_CONSOLE_GETCHAR=n
CONFIG_CONSOLE=n
CONFIG_RTT_CONSOLE=n
CONFIG_UART_CONSOLE=n

# Enable SUPL client support AGPS
CONFIG_SUPL_CLIENT_LIB=n

# Network
CONFIG_NETWORKING=y
CONFIG_NET_NATIVE=n
CONFIG_NET_SOCKETS=y
CONFIG_NET_SOCKETS_OFFLOAD=y
CONFIG_NET_SOCKETS_POSIX_NAMES=y
CONFIG_NET_SOCKETS_SOCKOPT_TLS=y

# LTE link control
CONFIG_LTE_LINK_CONTROL=y
CONFIG_LTE_AUTO_INIT_AND_CONNECT=n
#add by liming
#CONFIG_POWER_OPTIMIZATION_ENABLE=n
CONFIG_LTE_NETWORK_MODE_LTE_M_GPS=n
#CONFIG_LTE_LINK_CONTROL_LOG_LEVEL_DBG=y
CONFIG_LTE_NETWORK_MODE_NBIOT_GPS=y
CONFIG_LTE_LEGACY_PCO_MODE=y
#CONFIG_LTE_PSM_REQ_RPTAU="00000110"
#CONFIG_LTE_PSM_REQ_RAT="00000010"

# MQTT
CONFIG_MQTT_LIB=y
CONFIG_MQTT_LIB_TLS=y   
#add by liming
CONFIG_MQTT_CLIENT_ID="devzone_client"
CONFIG_MQTT_BROKER_HOSTNAME="test.mosquitto.org"
CONFIG_MQTT_BROKER_PORT=8884
CONFIG_SEC_TAG=51966
CONFIG_PEER_VERIFY=1

# Appliaction
#CONFIG_MQTT_PUB_TOPIC="/my/publish/topic"
#CONFIG_MQTT_SUB_TOPIC="/my/subscribe/topic"
#CONFIG_MQTT_CLIENT_ID="my-client-id"
#CONFIG_MQTT_BROKER_HOSTNAME="mqtt.eclipse.org"
#CONFIG_MQTT_BROKER_PORT=1883

# Library for buttons and LEDs
CONFIG_DK_LIBRARY=y
CONFIG_DK_LIBRARY_INVERT_LEDS=n

# Heap and stacks
CONFIG_HEAP_MEM_POOL_SIZE=16384
CONFIG_MAIN_STACK_SIZE=8192
CONFIG_SYSTEM_WORKQUEUE_STACK_SIZE=2048
CONFIG_HW_STACK_PROTECTION=y

# MCUBOOT
CONFIG_BOOTLOADER_MCUBOOT=y
CONFIG_IMG_MANAGER=y
CONFIG_MCUBOOT_IMG_MANAGER=y

# SPI
CONFIG_SPI=y
CONFIG_SPI_NRFX=y
CONFIG_SPI_2=y
CONFIG_SPI_2_NRF_SPIM=y
CONFIG_SPI_3=y
CONFIG_SPI_3_NRF_SPIM=y

# I2C
CONFIG_I2C=y
CONFIG_I2C_NRFX=y
CONFIG_I2C_1=y
CONFIG_I2C_1_NRF_TWIM=y
CONFIG_I2C_2=n
CONFIG_I2C_2_NRF_TWIM=n
CONFIG_I2C_INIT_PRIORITY=60

# UART
CONFIG_SERIAL=y
CONFIG_UART_INTERRUPT_DRIVEN=y
#CONFIG_UART_LINE_CTRL=y
#CONFIG_UART_0_NRF_UART=y
#CONFIG_UART_0_NRF_UARTE=y
#CONFIG_UART_0_NRF_FLOW_CONTROL=n
#CONFIG_UART_1_NRF_UARTE=n
#CONFIG_UART_1_NRF_FLOW_CONTROL=n

# Use smaller buffers for net_buf as CANBUS packets are quite small.
CONFIG_NET_BUF_DATA_SIZE=64
CONFIG_NET_BUF_USER_DATA_SIZE=1

# Main thread
CONFIG_MAIN_STACK_SIZE=8192
CONFIG_HEAP_MEM_POOL_SIZE=4096

[Carl Richard]

Hi!

To me it sounds like your device is not actually connected to the network when CESQ is queried. The problem in this ticket was due to PSM being used, so I would appreciate if you could open a new ticket on the matter as it's somewhat unrelated. 

I cannot see anything out of the ordinary in your prj.conf, but I guess this behavior is more related to the program flow of the application.

Best regards,
Carl Richard