In the process of sorting a completely unrelated issue, I believe we have stumbled across what may be an error in the firmware implementation of AT+CMGL in PDU mode. We have reproduced the problem on multiple modems of these two models, running on different LTE service providers (so, provider MBN files less likely to be implemented).
With no SMS currently stored in memory, in PDU mode (AT+CMGF? verified returns 0), we expect:
AT+CMGL=4
OK
Observed behavior:
AT+CMGF?
+CMGF: 0
OK
AT+CMGL=4
+CMS ERROR: 303
Additional behaviors we can see around this behavior:
AT+CMGF=0
OK
AT+CMGL=?
+CMGL: (“REC UNREAD”,“REC READ”,“STO UNSENT”,“STO SENT”,“ALL”)
OK
AT+CMGF=1
OK
AT+CMGL=?
+CMGL: (“REC UNREAD”,“REC READ”,“STO UNSENT”,“STO SENT”,“ALL”)
OK
Instead, we expected to see (from an EP06-E):
AT+CMGF?
+CMGF: 0
OK
AT+CMGL=?
+CMGL: (0-4)
OK
AT+CMGF=1
OK
AT+CMGL=?
+CMGL: (“REC UNREAD”,“REC READ”,“STO UNSENT”,“STO SENT”,“ALL”)
OK
Essentially, when SMS format is text mode, the command works normally (and we can send and receive texts using text mode). We can bulk read messages from memory using AT+CMGL=“ALL” and get the expected results. However, if we switch to PDU mode, the behavior of AT+CMGL does not appear to switch modes properly, and our attempts to perform a bulk read in the same way fail with the error message shown above.
So far, the following firmwares we have in our possession are confirmed affected:
EP06ALAR02A07M4G
EM06ALAR03A05M4G
Is this a known issue? We thought we might be crazy for the last few days, when we stumbled upon this while working on this unrelated issue. We waited to inquire until we were able to have several other people with EP06-A or EM06-A on other networks (without Verizon MBN active) confirm.
Thank you!