Just resolved a nasty timing issue regarding AT-commands and serial auto-baud config on our SIM7070 NB-IoT module. Phew! 😅
The MB-IoT module talks to our system via a serial interface using AT commands. Our PPP daemon for the mobile data connection needs to send various AT commands (using ChatScript), but communication didn't work in the first place.
Well - it worked when using the serial-to-USB converter, but it did not work via the native serial connection. The datasheet mentions that by default "auto-baud" is enabled, which tries to configure the module's baud rate by detecting a predefined bit sequence. That is why we need to send an "AT" before we issue any more AT commands. We do that - but probably we're too fast sending the next AT command, because if we introduce a bit of delay by sending another "AT", everything works fine. 🥳
Probably the serial-to-usb converter introduces just enough delay to make it work properly. 🤔
