We use nRF9160 on our own board.
The firmware "Serial lte modem" is installed on the chip with connection to an external MCU.
We need to publish the JSON messages larger than 256 bytes (up to 2000 bytes) to the broker.
We transmit data in "Data Mode" and receive confirmation to publish messages.
For the test we are sending 356 bytes, here is the AT command sequence:
2022-03-09T08:49:53.339Z INFO Modem port is opened
2022-03-09T08:49:54.456Z DEBUG modem >> AT
2022-03-09T08:49:54.471Z DEBUG modem << OK
2022-03-09T08:49:55.439Z DEBUG modem >> AT+CFUN?
2022-03-09T08:49:55.453Z DEBUG modem << +CFUN: 0
2022-03-09T08:49:55.462Z DEBUG modem << OK
2022-03-09T08:49:58.061Z INFO Updating CA certificate...
2022-03-09T08:49:58.063Z DEBUG modem >> AT%CMNG=0,321,0,"-----BEGIN CERTIFICATE-----
2022-03-09T08:49:58.343Z DEBUG modem >> -----END CERTIFICATE-----"
2022-03-09T08:49:58.499Z DEBUG modem << OK
2022-03-09T08:49:58.500Z INFO Updating client certificate...
2022-03-09T08:49:58.502Z DEBUG modem >> AT%CMNG=0,321,1,"-----BEGIN CERTIFICATE-----
2022-03-09T08:49:58.702Z DEBUG modem >> z6s4x54=
2022-03-09T08:49:58.715Z DEBUG modem >> -----END CERTIFICATE-----"
2022-03-09T08:50:00.457Z DEBUG modem << OK
2022-03-09T08:50:00.459Z INFO Updating private key...
2022-03-09T08:50:00.460Z DEBUG modem >> AT%CMNG=0,321,2,"-----BEGIN EC PRIVATE KEY-----
2022-03-09T08:50:00.512Z DEBUG modem >> -----END EC PRIVATE KEY-----"
2022-03-09T08:50:00.711Z DEBUG modem << OK
2022-03-09T08:50:00.712Z INFO Certificate update completed
2022-03-09T08:50:21.135Z DEBUG modem >> AT+CEREG=5
2022-03-09T08:50:21.148Z DEBUG modem << OK
2022-03-09T08:50:24.911Z DEBUG modem >> AT+CFUN=1
2022-03-09T08:50:24.952Z DEBUG modem << OK
2022-03-09T08:50:25.923Z DEBUG modem << +CEREG: 2,"026F","00332521",7
2022-03-09T08:50:28.862Z DEBUG modem << +CEREG: 5,"026F","00332521",7,,,"00011110","11100000"
2022-03-09T08:50:35.864Z DEBUG modem >> AT#XMQTTCON=1,"999876","","","a34k7wa09ujucc-ats.iot.us-east-1.amazonaws.com",8883,321
2022-03-09T08:50:36.869Z ERROR Error: 'AT#XMQTTCON=1,"999876","","","a34k7wa09ujucc-ats.iot.us-east-1.amazonaws.com",8883,321
' timed out
2022-03-09T08:50:38.506Z DEBUG modem << OK
2022-03-09T08:50:38.810Z DEBUG modem << #XMQTTEVT: 0,0
2022-03-09T08:50:57.167Z DEBUG modem >> AT#XMQTTPUB="Rigel/ToServer/v2/AR_TEST","",1
2022-03-09T08:51:08.472Z DEBUG modem >> {"deviceId":"","deviceType":"Collar","requestTime":0,"carrier":"CELLULAR","rssi":-70,"messages":[{"messageId":536875008,"messageCategory":1,"messageType":9,"recordedTime":0,"firmwareVersion":"collar-fw-0.1.3","bootVersion":"collar-boot-0.0.1","attachmentStatus":"Unknown","battery":0,"chargeStatus":0,"operationMode":0,"debugMode":0,"sos":0,"safeZone":0}]}
2022-03-09T08:51:09.258Z DEBUG modem << #XMQTTEVT: 3,0
2022-03-09T08:52:08.971Z DEBUG modem << #XMQTTEVT: 9,0But from the server side, we always receive messages with a maximum length of 256 bytes (truncated):
{"deviceId":"","deviceType":"Collar","requestTime":0,"carrier":"CELLULAR","rssi":-70,"messages":[{"messageId":536875008,"messageCategory":1,"messageType":9,"recordedTime":0,"firmwareVersion":"collar-fw-0.1.3","bootVersion":"collar-boot-0.0.1","attachmentStThere are no problems when transmitting a message via UART, we record everything that we transmit via "Logic" App, and clearly saw that the message via UART was completely gone.
Plus, we also saw the same problem when we subscribe to the topic. If we wait to receive messages larger than 256 bytes, it comes truncated and after we receive event for a read error and a disconnect.2022-03-08T15:29:20.381Z DEBUG modem >> AT#XMQTTSUB="Rigel/ToServer/v2/AR_TEST",0
2022-03-08T15:29:21.134Z DEBUG modem << OK
2022-03-08T15:29:21.612Z DEBUG modem << #XMQTTEVT: 7,0
2022-03-08T15:29:24.096Z DEBUG modem << Rigel/ToServer/v2/AR_TEST
2022-03-08T15:29:31.789Z DEBUG modem << {"deviceId":"","deviceType":"Collar","requestTime":0,"carrier":"CELLULAR","rssi":-70,"messages":[{"messageId":536875008,"messageCategory":1,"messageType":9,"recordedTime":0,"firmwareVersion":"collar-fw-0.1.3","bootVersion":"collar-boot-0.0.1","attachmentSt#XMQTTEVT: 2,0#XMQTTMSG: 29,256Rigel/ToServer/v2/Operational{"deviceId":"","deviceType":"Collar","requestTime":0,"carrier":"CELLULAR","rssi":-70,"messages":[{"messageId":536875008,"messageCategory":1,"messageType":9,"recordedTime":0,"firmwareVersion":"collar-fw-0.1.3","bootVersion":"collar-boot-0.0.1","attachmentSt
2022-03-08T15:29:44.526Z DEBUG modem << #XMQTTEVT: 2,0
2022-03-08T15:29:44.689Z DEBUG modem << #XMQTTEVT: 2,-122
2022-03-08T15:29:44.700Z DEBUG modem << #XMQTTEVT: 1,-113
