console_uart.c
The serial console rides the UART wired to the MDK debugger: lightweight printf, echo of received characters, tick counter. The first debugging tool of any nRF project, no JTAG probe needed.
Hardware
An nRF52840-MDK board (Nordic nRF52840, Cortex-M4F @ 64 MHz, 1 MB flash / 256 KB RAM, BLE 5 + 802.15.4) with onboard debugger, programmed in C with nRF5 SDK v17 and the S140 SoftDevice. nRF52840-MDK plugged to the PC over its USB (the debugger exposes a serial port).
Wiring
No wiring when keeping the debugger pins; otherwise crossed TX/RX to a 3.3 V USB-serial adapter.
How it works
app_uart sets up the UART (configurable pins and baudrate), print formats on the stack then sends byte by byte; app_uart_get drains the RX FIFO.
Running it
Open the matching nRF5 SDK v17 example (custom_board target), paste this code into main.c, build with Segger Embedded Studio or the gcc Makefile, then flash through the onboard debugger.
Variants
Switch to UARTE + EasyDMA for real throughput, or redirect printf through _write (newlib) for standard printf.
console_uart.c
// nRF52840-MDK : console UART via le debugger intégré (puce J-Link/CP210x).
// Broches SDK par défaut (custom_board) : TX P0.06 / RX P0.08 — adapter si besoin.
#include <stdio.h>
#include <stdarg.h>
#include "nrf_drv_uart.h"
#include "app_uart.h"
static void uart_init(void) {
nrf_drv_uart_config_t cfg = NRF_DRV_UART_DEFAULT_CONFIG;
cfg.pseltxd = 6; // TX : vérifier le schéma de la carte
cfg.pselrxd = 8; // RX
cfg.baudrate = NRF_UART_BAUDRATE_115200;
app_uart_init(&cfg);
}
static void print(const char *fmt, ...) {
char buf[128];
va_list ap; va_start(ap, fmt);
int n = vsnprintf(buf, sizeof buf, fmt, ap);
va_end(ap);
for (int i = 0; i < n; i++) app_uart_putc(buf[i]);
}
int main(void) {
uart_init();
print("\nnRF52840-MDK — console OK\n");
uint32_t n = 0;
for (;;) {
uint8_t octet;
while (app_uart_get(&octet) == NRF_SUCCESS) { // écho RX
app_uart_putc(octet);
print("[recu 0x%02X]\n", octet);
}
if (++n % 500000 == 0) print("tick %u\n", n / 500000);
}
}