UART P0.01 pin stays low

[Varouzan]

Hi all,

I am trying to set up UART communication on the nrf9160. I am using the nrf9160 DK and zephyr.

I have selected device UART_1 and after I cal functions device get_binding() and uart_configure() I can send data over the the virtual port VCOM2.

However TX pin P0.01 stays LOW all the time. Does anybody know anything about this issue?

nrf9160_pca.dts_compliled snippet

uart1: uart@9000 {
				compatible = "nordic,nrf-uarte";
				reg = < 0x9000 0x1000 >;
				interrupts = < 0x09 0x01 >;
				status = "okay";
				label = "UART_1";
				current-speed = < 0x1c200 >;
				tx-pin = < 0x01 >;
				rx-pin = < 0x00 >;
				rts-pin = < 0x0e >;
				cts-pin = < 0x0f >;
			};

proj.config snippet:

CONFIG_SERIAL=y
CONFIG_TRUSTED_EXECUTION_NONSECURE=y
CONFIG_UART_INTERRUPT_DRIVEN=y
CONFIG_UART_0_NRF_UARTE=y
CONFIG_UART_1_NRF_UARTE=y

struct device *uart_dev;

void uart_init(void){
  int err=0;
  struct uart_config uart_settings;
  uart_dev = device_get_binding(UART_NAME);
  if(uart_dev == NULL){
    printk("error:could not get %s binding\n",UART_NAME);
    return;
  }
  uart_settings.baudrate = 115200;
  uart_settings.parity = UART_CFG_PARITY_NONE;
  uart_settings.stop_bits = UART_CFG_STOP_BITS_1;
  uart_settings.data_bits = UART_CFG_DATA_BITS_8;
  uart_settings.flow_ctrl = UART_CFG_FLOW_CTRL_NONE;
  err = uart_configure(uart_dev,&uart_settings);
  if(err == 0){
    printk("configured uart\n");
    printk("Value of NRF_UARTE1_NS->PSEL.RXD: %lu \n",  (unsigned long)NRF_UARTE1_NS->PSEL.RXD);
    printk("Value of NRF_UARTE1_NS->PSEL.TXD: %lu \n",  (unsigned long)NRF_UARTE1_NS->PSEL.TXD);
  }
  else{
    printk("error could not configure uart\n");
  }

}

int main(void) {
  printk("Starting application\n");

  uart_init();
  
  u8_t string[] ="AWAKE\r\n";
  u8_t* test_ptr = string;

  while (true) {

   for(int i=0; i<sizeof(string);i++){
    uart_poll_out(uart_dev,*test_ptr);
    //printk("%c",*test_ptr);
    test_ptr++;
   }
   test_ptr = string;
   k_sleep(100);
  }

  return 0;
}

[Simon]

I tested your example, and was able to see the output ("AWAKE"), which means the TX pin is not low all the time. Are you able to see the serial output? How did you measure it? If you are measuring on P0.01 on the DK you will not see the activity on the TX pin, since the GPIO is routed to the interface MCU instead.

Best regards,

Simon

[Varouzan]

Hello Simon,

I do see the output 'AWAKE' through the COM port.  I am also measuring the P0.01 pin with a scope probe and it always stays low. How can I reroute to the GPIO instead?

Best regards,

Varouzan

[Simon]

Here is a thread that explains how to do that. If you have any questions beyond that, please ask and I will assist you.

Best regards,

Simon