Max QMTRECV length for BG770?

IoT Modules LPWA Module
1

Docs state that QMTPUB has a tx limit of 4096 bytes, which I’ve tested and found to be true :slight_smile:

Docs don’t mention if there’s any limit for QMTSUB/QMTRECV.
Is there a limit, and if so where is this documented?

Thanks!
-Dave

2

Currently BG770 only supports direct output mode, QMTRCV has no restrictions

3

I’m finding that’s not the case.

  • When I SUB to one of my topics that sends “less” data (<2k of JSON) the modem sends me the QMTRECV with the expected payload and it always succeeds.
  • When I SUB to a topic that is known to send “more” data (~9k of JSON) the server shows that it sent the payload but the modem never sends me a QMTRECV (or any other indication).

So, clearly there’s some limit (similar to the modem’s 4k limit for QMTPUB).
I could experiment to find out what it is, but I’d prefer to hear the actual value from Quectel’s tech folks.

Additionally: Can you tell me why the modem doesn’t send me any indication that anything happened? Even a “too much data” response would be better than my having to time out because otherwise I’d be waiting forever for a response that will never come.

4

image
image1034×605 100 KB

if msg_recv_mode=0,it is not limited
if msg_recv_mode=1,it is limited,Typically, there are five messages, each of which is 4K in size

5

If I don’t set this, which is the default, msg_recv_mode 0 or 1?

6

I’m now explicitly setting AT+QMTCFG="recv/mode",4,0 but I still don’t receive the QMTRECV when the server sends >4k of JSON.

Is there something else I should be doing?

7

pls run and query

AT+QGMR
ATI
AT+CGSN

8

AT+QGMR?
BG770AGLAAR01A05_BETA240209A_01.200.01.200_BETA240209A

ATI
Quectel
BG770A-GL
Revision: BG770AGLAAR01A05_BETA240209A

AT+CGSN
863593053696050