Hi everyone,
We’re trying to use UART1 on the nRF9151 DK in non-secure mode, mapped to the Arduino R1 connector. However, it seems to be reserved by TF-M, and we cannot disable TF-M because we also need LTE functionality.
We even tried disabling VCOM1 using the Board Configurator, but it didn’t help.
According to the documentation, it should be possible to free UART1 by disabling a configuration, but in our setup it doesn’t work.
We’ve attached our main.c, prj.conf, and .overlay files for reference.
Has anyone successfully used UART1 in non-secure mode while keeping TF-M enabled? Any guidance or examples would be greatly appreciated.
Thanks in advance!
main.cpp:
/*
* Minimal UART echo (polling) for Zephyr
*/
#include <zephyr/kernel.h>
#include <zephyr/device.h>
#include <zephyr/drivers/uart.h>
#define UART_NODE DT_ALIAS(rs485_uart)
static const struct device *uart = DEVICE_DT_GET(UART_NODE);
int main(void)
{
if (!device_is_ready(uart))
{
return 0;
}
const char *banner = "UART polling echo\r\n";
for (const char *p = banner; *p; p++)
{
uart_poll_out(uart, *p);
}
while (true)
{
unsigned char c;
if (uart_poll_in(uart, &c) == 0)
{
uart_poll_out(uart, c);
}
else
{
k_msleep(1);
}
}
}
prj.conf:
# # Copyright (C) 2026 - OWL Services LLC # # This program is free software; you can redistribute it and/or modify it under # the terms of the GNU General Public License (version 2) as published by the # FSF - Free Software Foundation # # Compiler CONFIG_DEBUG_OPTIMIZATIONS=y # C Standard Library implementation CONFIG_NEWLIB_LIBC=y CONFIG_NEWLIB_LIBC_FLOAT_PRINTF=y # C++ support CONFIG_CPP=y CONFIG_REQUIRES_FULL_LIBCPP=y # Zephyr Kernel CONFIG_HEAP_MEM_POOL_SIZE=2048 CONFIG_IDLE_STACK_SIZE=320 CONFIG_ISR_STACK_SIZE=2048 CONFIG_SYSTEM_WORKQUEUE_STACK_SIZE=1152 CONFIG_MAIN_STACK_SIZE=4096 # Logging CONFIG_LOG=y CONFIG_LOG_MODE_IMMEDIATE=n CONFIG_APP_LOG_LEVEL_DBG=n CONFIG_CBPRINTF_FP_SUPPORT=y # ZBUS CONFIG_ZBUS=y # UART CONFIG_SERIAL=y # Zephyr Networking Layer CONFIG_NETWORKING=y CONFIG_NET_LOG=n CONFIG_NET_SOCKETS=y CONFIG_NET_SOCKETS_OFFLOAD=y CONFIG_NET_SOCKETS_SERVICE_STACK_SIZE=1200 CONFIG_NET_DEFAULT_IF_FIRST=y CONFIG_NET_CONFIG_SETTINGS=y CONFIG_NET_IPV4=y CONFIG_NET_IPV6=y CONFIG_NET_TCP=y CONFIG_NET_UDP=y CONFIG_NET_CONNECTION_MANAGER=y CONFIG_NET_MGMT=y CONFIG_NET_RX_STACK_SIZE=1792 CONFIG_NET_TX_STACK_SIZE=1200 CONFIG_DNS_RESOLVER=y CONFIG_POSIX_API=y # MQTT CONFIG_MQTT_LIB=y CONFIG_MQTT_LOG_LEVEL_DBG=n CONFIG_TFM_LOG_LEVEL_SILENCE=y
boards/nrf9151dk_nrf9151_ns.conf:
# # Copyright (C) 2026 - OWL Services LLC # # This program is free software; you can redistribute it and/or modify it under # the terms of the GNU General Public License (version 2) as published by the # FSF - Free Software Foundation # # UART CONFIG_UART_LINE_CTRL=y CONFIG_UART_INTERRUPT_DRIVEN=y # Modem CONFIG_NRF_MODEM_LIB=y # LTE CONFIG_LTE_LINK_CONTROL=y CONFIG_LTE_LINK_CONTROL_LOG_LEVEL_DBG=y CONFIG_LTE_LC_CONN_EVAL_MODULE=y CONFIG_LTE_LC_WORKQUEUE_STACK_SIZE=1024
boards/nrf9151dk_nrf9151_ns.overlay:
/*
* Copyright (C) 2026 - OWL Services LLC
*
* This program is free software; you can redistribute it and/or modify it under
* the terms of the GNU General Public License (version 2) as published by the
* FSF - Free Software Foundation
*
*/
/ {
aliases {
rs485-uart = &uart1;
rs485-de = &rs485de;
};
rs485de: rs485-de {
gpios = <&gpio0 15 GPIO_ACTIVE_HIGH>;
};
};
/* Pins are defined based on the carrier board usage and the specifications provided in the manual */
&pinctrl {
uart1_default: uart1_default {
group1 {
psels = <NRF_PSEL(UART_RX, 0, 28)>,
<NRF_PSEL(UART_TX, 0, 29)>;
};
};
uart1_sleep: uart1_sleep {
group1 {
psels = <NRF_PSEL(UART_RX, 0, 28)>,
<NRF_PSEL(UART_TX, 0, 29)>;
low-power-enable;
};
};
};
&uart1 {
status = "okay";
current-speed = <115200>;
pinctrl-0 = <&uart1_default>;
pinctrl-1 = <&uart1_sleep>;
pinctrl-names = "default", "sleep";
};
