app: Add overlay for UART1 hw-flow-control

Author: trantanen

app/overlay-uart1-hwfc.overlay

@@ -0,0 +1,9 @@
+/*
+ * Copyright (c) 2026 Nordic Semiconductor ASA
+ *
+ * SPDX-License-Identifier: LicenseRef-Nordic-5-Clause
+ */
+
+&uart1 {
+	hw-flow-control;
+};

doc/app/sm_configuration.rst

@@ -303,5 +303,9 @@ The following configuration files are provided:
   This overlay can be used if your setup does not have the need or means for managing the power externally.
   Modify the overlay to fit your configuration.
 
+* :file:`overlay-uart1-hwfc.overlay` - Devicetree overlay that enables hardware flow control on UART 1.
+  This is needed when capturing modem traces and application debug logs simultaneously.
+  See the :ref:`sm_logging` documentation for more information.
+
 The board-specific devicetree overlays (:file:`boards/*.overlay`) set up configurations that are specific to each supported development kit.
 All of them configure the DTR to be deasserted from a button and RI to blink an LED.

doc/app/sm_logging.rst

@@ -59,16 +59,7 @@ Use the `Cellular Monitor app`_ for capturing and analyzing modem traces.
    Modem traces captured through UART are corrupted if application logs through RTT are simultaneously captured.
    When capturing modem traces through UART with the `Cellular Monitor app`_ and simultaneously capturing RTT logs, for example, with J-Link RTT Viewer, the modem trace misses packets, and captured packets might have incorrect information.
 
-   If you need to capture modem traces and RTT logs at the same time, enable HW flow control for modem trace UART.
-   This can be done for the `nRF9151 DK <nrf9151dk_>`_ by adding the following change to :file:`app/boards/nrf9151dk_nrf9151_ns.overlay`:
-
-   .. parsed-literal::
-      :class: highlight
-
-      &uart1 {
-       hw-flow-control;
-      };
-
+   If you need to capture modem traces and RTT logs at the same time, enable HW flow control for modem trace UART (``-DEXTRA_DTC_OVERLAY_FILE=overlay-uart1-hwfc.overlay``).
    Otherwise, you can choose not to capture RTT logs.
    Having only RTT logs enabled does not cause this issue.