Limiting the amount of data received from AT#XRECV command.

[Daniel B. J.]

Hi,

We are updating an older platform with the nRF9151 on an add-on PCB.The platform has very limited processing power and buffer space.

The nRF9151 module with the at firmware is connected via UART without CTS/RTS connected. Our previous modules had the option to limit the amount of data received in the command used to get TCP/IP socket data, hence the lack of hardware flow control. We have one line of hardware communication we might be able to convert to a CTS connection, but it's sub optimal.

The question is if there's a command based way to limit the amount of data received through the UART from a TCP/IP socket via AT#XRECV or similar while using the at-firmware, or do we need to make either custom firmware for the nRF9151 module or hardware changes?

Kind regards,

Daniel.

[Syed Maysum Abbas Zaidi]

Hi,

Yes, #XRECV supports small reads. It has an optional <data_len> argument that lets you specify the maximum number of bytes to receive from the socket in a single call.
However, this only limits how much data is read per #XRECV and does not replace UART hardware flow control. If the Serial Modem UART RX buffers fill up, it will disable UART reception. Whereas when hw flow control (RTS/CTS) is enabled, the modem can pause the sender, but without it incoming UART data may be dropped. Therefore, its sill recommended to add at least CTS.

Best Regards,
Syed Maysum

[Daniel B. J.]

Hi,

Perfect, thank you.

It seems I had bookmarked an older version of the at-firmware documentation with a simpler version of #XRECV described.

Kind Regards,

Daniel.

[Daniel B. J.]

Hi,

I've run some test using the nRF91 firmware binaries v2.04 and the serial LTE modem firmware, and the at commands shown in the link you provided does not seem to match with the firmware I've tested.

What firmware should i download/build in order to use that version of the #XRECV command?

Kind regards, Daniel

[Syed Maysum Abbas Zaidi]

Hi,

Yes its correct that the old Serial LTE Modem (SLM) application does not have the new version of #XRECV command. It has been added in the Serial Modem Application which is available from NCS v3.2.0.

So either you start using newer NCS version (simpler) or if you want you can also migrate from the SLM to serial modem by making changes as mentioned in this link.

Best Regards,
Syed Maysum