Compilation of nRF9151 project with TF-M log routed to UART0 results in error "undefined reference to stdio_init"

Question

I'm developing a project, where I use nRF9151 as a GPS sensor, and nRF52833 as a BLE gateway. I want to send data from 9151 to 52833 over one of UARTs. The problems I'm facing now are either runtime or compile time, depending on the set of configurations. I was able to reproduce this issue on the nRF9151DK.

This demo consists of 3 files.
main.c:

#include <zephyr/kernel.h>
#include <zephyr/logging/log.h>
#include <zephyr/drivers/uart.h>

#include <nrf_modem_gnss.h>
#include <modem/nrf_modem_lib.h>

#include <modem/lte_lc.h>


LOG_MODULE_REGISTER(main_app, LOG_LEVEL_DBG);

int main(void)
{
 LOG_DBG("Starting main app thread on hw %s", CONFIG_BOARD);
 return 0;
}


const struct device * uart_1 = DEVICE_DT_GET(DT_NODELABEL(uart1));


void uart1_thread(void* p1, void* p2, void* p3)
{
 LOG_DBG("Starting UART1 thread");

 if (!device_is_ready(uart_1))
 {
 LOG_ERR("UART1 init failed");
 }

 const struct uart_config uart_cfg = {
 .baudrate = 115200,
 .parity = UART_CFG_PARITY_NONE,
 .stop_bits = UART_CFG_STOP_BITS_1,
 .data_bits = UART_CFG_DATA_BITS_8,
 .flow_ctrl = UART_CFG_FLOW_CTRL_NONE
 };

 int err = uart_configure(uart_1, &uart_cfg);
 if (err != 0) {
 LOG_ERR("UART1 init failed %d", err);
 }

 uint8_t tx_buff[32] = {0};
 snprintf(tx_buff, 20, "%s\n", "hello world\n");

 while(1)
 {
 k_msleep(1000);
 uart_tx(uart_1, tx_buff, 20, SYS_FOREVER_MS);
 LOG_DBG("UART 1 msg sent");
 }
}

K_THREAD_DEFINE(uart1_thr_id, 1024, uart1_thread, NULL, NULL, NULL, 6, 0, 10);

static int modem_configure(void)
{
 int err;

 LOG_INF("Initializing modem library");

 err = nrf_modem_lib_init();
 if (err) {
 LOG_ERR("Failed to initialize the modem library, error: %d", err);
 return err;
 }

 return 0;
}


void gps_thread(void* p1, void* p2, void* p3)
{
 LOG_DBG("Starting GPS thread");

 modem_configure();

 LOG_DBG("func mode set");
 // if (lte_lc_func_mode_set(LTE_LC_FUNC_MODE_ACTIVATE_GNSS) != 0) {
 if (lte_lc_func_mode_set(LTE_LC_FUNC_MODE_NORMAL) != 0) {
 LOG_ERR("Failed to activate GNSS functional mode");
 return;
}

 while(1)
 {
 k_msleep(5000);
 LOG_DBG("GPS cycle");
 }
}

K_THREAD_DEFINE(gps_thr_id, 1024, gps_thread, NULL, NULL, NULL, 6, 0, 10);


prj.conf (it's taken from another project, so it's not a minimal subset of configs)


CONFIG_GPIO=y

CONFIG_SHELL=y
CONFIG_KERNEL_SHELL=y

CONFIG_SERIAL=y

CONFIG_SHELL_BACKEND_SERIAL=y
CONFIG_SHELL_VT100_COMMANDS=y
CONFIG_SHELL_VT100_COLORS=y
CONFIG_SHELL_STACK_SIZE=4096
CONFIG_SHELL_CMD_BUFF_SIZE=128

CONFIG_SHELL_WILDCARD=n
CONFIG_SHELL_HELP_ON_WRONG_ARGUMENT_COUNT=n
CONFIG_SHELL_STATS=n
CONFIG_SHELL_CMDS=n
CONFIG_SHELL_HISTORY=y

CONFIG_DEBUG_OPTIMIZATIONS=y
CONFIG_DEBUG_THREAD_INFO=y

# Enable CPP support
CONFIG_CPP=y

CONFIG_LOG=y
CONFIG_LOG_DEFAULT_LEVEL=3

CONFIG_REBOOT=y

CONFIG_CONSOLE=y
CONFIG_UART_CONSOLE=y

CONFIG_NRF_MODEM_LIB=y
CONFIG_NRF_MODEM_LIB_LOG_FW_VERSION_UUID=y

CONFIG_LTE_LINK_CONTROL=y
CONFIG_LTE_NETWORK_MODE_LTE_M_GPS=y

CONFIG_NRF_MODEM_LIB_FAULT_STRERROR=n

CONFIG_HEAP_MEM_POOL_SIZE=4096
CONFIG_MAIN_STACK_SIZE=4096
CONFIG_SYSTEM_WORKQUEUE_STACK_SIZE=1536

# CONFIG_AT_HOST_LIBRARY=y
CONFIG_NRF_MODEM_LIB_SHMEM_RX_SIZE=8192
CONFIG_NRF_MODEM_LIB_SHMEM_TX_SIZE=8192


CONFIG_UART_ASYNC_API=y
CONFIG_UART_0_ASYNC=n
#CONFIG_UART_1_ASYNC=y
#CONFIG_UART_1_INTERRUPT_DRIVEN=n
CONFIG_UART_USE_RUNTIME_CONFIGURE=y

CONFIG_TFM_SECURE_UART0=y
#CONFIG_TFM_LOG_LEVEL_SILENCE=y

nrf9151dk_nrf9151.overlay

&pinctrl {
 uart0_default: uart0_default {
 group1 {
 psels = <NRF_PSEL(UART_TX, 0, 18)>,
 <NRF_PSEL(UART_RX, 0, 17)>;
 };
 };

 uart0_sleep: uart0_sleep {
 group1 {
 psels = <NRF_PSEL(UART_TX, 0, 18)>,
 <NRF_PSEL(UART_RX, 0, 17)>;
 low-power-enable;
 };
 };

 uart1_default: uart1_default {
 group1 {
 psels = <NRF_PSEL(UART_TX, 0, 22)>,
 <NRF_PSEL(UART_RX, 0, 21)>;
 };
 };
 uart1_sleep: uart1_sleep {
 group1 {
 psels = <NRF_PSEL(UART_TX, 0, 22)>,
 <NRF_PSEL(UART_RX, 0, 21)>;
 low-power-enable;
 };
 };

};

&uart0 {
 compatible = "nordic,nrf-uarte";
 status = "okay";
 current-speed = <115200>;
 pinctrl-0 = <&uart0_default>;
 pinctrl-1 = <&uart0_sleep>;
 pinctrl-names = "default", "sleep";
};

&uart1 {
 compatible = "nordic,nrf-uarte";
 status = "okay";
 current-speed = <115200>;
 pinctrl-0 = <&uart1_default>;
 pinctrl-1 = <&uart1_sleep>;
 pinctrl-names = "default", "sleep";
};

I use nRF Connect SDK 3.0.2.

I'm trying to follow this manual: https://docs.nordicsemi.com/bundle/ncs-latest/page/nrf/security/tfm/tfm_logging.html. 

When I use config CONFIG_TFM_SECURE_UART0 , compilation fails with the following error:
nrf-sdk/v3.0.2/modules/tee/tf-m/trusted-firmware-m/platform/ext/target/nordic_nrf/common/core/tfm_hal_platform_common.c:36: undefined reference to `stdio_init'

When at the same time I use config CONFIG_TFM_LOG_LEVEL_SILENCE=y, compilation works, but when I flash the DK - the board stays silent on both UARTs.

I've also attempted changing TF-M logging properties inside the Kconfig, but it was always resulting either in various compilation errors or a silent board.

Primary question of this post: what config would allow me to compile and link file `uart_stdout.c` (the definition of stdio_init is there)? I have an impression that I'm missing a simple configuration flag.
More global (and more important to me) question: is there a comprehensive guide on how to reliably use UART1 in nRF9151 for inter-MCU communication on a system with TF-M (which is required to run modem firmware)? All my attempts so far ended either in: compilation error, silent board or runtime errors, throwing a secure fault on the first call to the `uart_tx` method of Zephyr UART API

roman.turkin · Answer

I did not find the solution to the underlying TF-M related problem, but have managed to find the solution of the compilation time problem. Recipe: do not rely on the command "clean build configuration"/"pristine build". Only explicit removal of the build directory and recreation of the build configuration helps to achieve a reliable behavior of the build system. After I started removing the build folder upon every major change in either defconfig or prj.conf, these sporadic compilation issues were gone.