UART TX pin pulls down during reset

[ivank4]

On the picture channel 2 connected to reset button on PDK.

UART channel drops to GND 4ms after button pressed.

How to prevent this? 

Tried this: https://devzone.nordicsemi.com/f/nordic-q-a/25591/uart-hits-communication-error/100873#100873

no changes.

Code works fine with external board (STM32) until reset or full hardware power down and power on causes pull-down.

• nRF52840-Preview_DK(PCA10056) 0.9.3
• Segger Embedded Studio.
• Code based on UART example
• RTT enabled

#include <stdbool.h>
#include <stdint.h>
#include <stdio.h>
#include "app_uart.h"
#include "app_error.h"
#include "nrf_delay.h"
#include "nrf.h"
#include "bsp.h"
#include "protocol.h"
#include "app_timer.h"
#include "nordic_common.h"
#include "nrf_error.h"
#include "nrf_drv_clock.h"

//logging
#include "nrf_log.h"
#include "nrf_log_ctrl.h"
#include "nrf_log_default_backends.h"

#include "nrf_uart.h"


#define MAX_TEST_DATA_BYTES     (15U)                /**< max number of test bytes to be used for tx and rx. */
#define UART_TX_BUF_SIZE 64                         /**< UART TX buffer size. */
#define UART_RX_BUF_SIZE 16                         /**< UART RX buffer size. */


#define rcvd_max_data_len 12
static ConfPack cmd;

static uint8_t index = 0;
static uint8_t err_count = 0;

APP_TIMER_DEF(m_singleshot_timer_on);     /* Handler for repeated timer used to send on cmd throught uart. */
APP_TIMER_DEF(m_singleshot_timer_off);   /* Handler for repeated timer used to send off cmd throught uart. */


//Function starting the internal LFCLK oscillator.
static void lfclk_request(void)
{
    ret_code_t err_code = nrf_drv_clock_init();
    APP_ERROR_CHECK(err_code);
    nrf_drv_clock_lfclk_request(NULL);
}


#define CRC32_POLY   0x04C11DB7

uint32_t STM_crc_32_update(uint32_t crc, uint32_t data)
{
    crc = crc ^ data;
    for(uint32_t i=0;i<32;i++)
        if (crc & 0x80000000)
            crc = (crc << 1) ^ CRC32_POLY;
        else
            crc = (crc << 1);
    return(crc);
}


uint32_t crc32_4byte( uint32_t *buf, int len)
{
    uint32_t v;
    uint32_t crc;
    crc = 0xFFFFFFFF;
    while(len >= 4) {
        v = (*buf++);
        crc = STM_crc_32_update(crc,v);
        len-=4;
    }
    
    return crc;
}

void uart_event_handle(app_uart_evt_t * p_event)
{
    static uint8_t data_array[rcvd_max_data_len];
    uint32_t       err_code;

    switch (p_event->evt_type)
    {
        case APP_UART_DATA_READY:
            /*
            app_timer_stop(m_singleshot_timer_id);
            app_timer_start(m_singleshot_timer_id, APP_TIMER_TICKS(50), NULL);
            */
            //timer restart
            err_code = app_uart_get(&data_array[index]);
            APP_ERROR_CHECK(err_code);
            index++;    
                if (index = 12) //received full length packet
                {   
                    StatPack spack;
                    uint32_t crc;
                    memcpy((void*)&spack,data_array,sizeof(StatPack));
                    crc = crc32_4byte((uint32_t*)data_array,sizeof(StatPack));
                    if((spack.rep.slave_stat&VER_MASK) == FW_VERSION<<8)   //header check
                    {
                      if (crc == 0)                       //CRC check
                      {
                          bsp_board_led_invert(1);
                          //==manage data==
                          /*
                          =spack.rep.current;
                          =spack.rep.rpm;
                          =spack.rep.slave_stat;
                          =spack.rep.voltage;
                          */

                        //flushes
                        index = 0;
                        err_count = 0;
                      }else{
                        //move data 1 byte left
                        for(int j=0; j<(rcvd_max_data_len-1); j++){
                          data_array[j]=data_array[j+1];
                        }
                        index--;//CRC check will be repeted
                        err_count++;
                      }
                    } else { //case version error! err_count++;
                      bsp_board_led_invert(2);
                      for(int j=0; j<(rcvd_max_data_len-1); j++){
                        data_array[j]=data_array[j+1];
                      }
                      index--;//CRC check will be repeted
                      err_count++;
                    }
                }else if(index > 12){
                   bsp_board_led_on(3);//How it happens on power off?
                   index = 0;
                
                }else if(err_count > 12){
                   app_uart_flush();//buffers flush                  
                   //flushes
                        index = 0;
                        err_count = 0;
                   bsp_board_led_invert(3);
                }  
            break;

        /*case APP_UART_COMMUNICATION_ERROR:
            APP_ERROR_HANDLER(p_event->data.error_communication);
            break;
        */
        case APP_UART_FIFO_ERROR:
            APP_ERROR_HANDLER(p_event->data.error_code);          
            break;

        default:
            break;
    }
}

static void timer_on_handler(void * p_context){
  
  bsp_board_led_on(0);
  
  uint32_t err_code;
  cmd.conf.dgain=0;
  cmd.conf.igain=0;
  cmd.conf.linstep=0;
  cmd.conf.oc_current=2000;
  cmd.conf.pgain=8;
  cmd.conf.rpm_set=5000;
  cmd.conf.uv_voltage=10000;
  
    cmd.conf.master_stat = (1<<8);
    cmd.conf.master_stat |= MVER;
    cmd.conf.master_stat |= SET_OCUV;
    cmd.conf.master_stat &= ~SET_PID_K;
    cmd.conf.master_stat &= ~SET_PID;
    cmd.conf.master_stat |= SET_RPM_MOD;
    cmd.conf.master_stat &= ~RUN_CAL;
  
  cmd.crc=crc32_4byte((uint32_t*)&cmd.conf,sizeof(cmd.conf)); 
  
  uint8_t cmd_send_buf[sizeof(cmd)];
  memcpy((void*)&cmd_send_buf, &cmd, sizeof(cmd));

  for (int i=0;i<sizeof(cmd);i++){
    while (app_uart_put(cmd_send_buf[i]) != NRF_SUCCESS);
  }
}

static void timer_off_handler(void * p_context){
  bsp_board_led_off(0);
  uint32_t err_code;
  cmd.conf.dgain=0;
  cmd.conf.igain=0;
  cmd.conf.linstep=0;
  cmd.conf.oc_current=2000;
  cmd.conf.pgain=8;
  cmd.conf.rpm_set=0;
  cmd.conf.uv_voltage=10000;
  
    cmd.conf.master_stat = (1<<8);
    cmd.conf.master_stat |= MVER;
    cmd.conf.master_stat |= SET_OCUV;
    cmd.conf.master_stat &= ~SET_PID_K;
    cmd.conf.master_stat &= ~SET_PID;
    cmd.conf.master_stat |= SET_RPM_MOD;
    cmd.conf.master_stat &= ~RUN_CAL;
  
  cmd.crc=crc32_4byte((uint32_t*)&cmd.conf,sizeof(cmd.conf));
  
  uint8_t cmd_send_buf[sizeof(cmd)];
  memcpy((void*)&cmd_send_buf, &cmd, sizeof(cmd));
  
  for (int i=0;i<sizeof(cmd);i++){
    while (app_uart_put(cmd_send_buf[i]) != NRF_SUCCESS);
  }  
}


static void create_timers()
{
    ret_code_t err_code = app_timer_init();
    APP_ERROR_CHECK(err_code);
    
    err_code = app_timer_create(&m_singleshot_timer_on, APP_TIMER_MODE_SINGLE_SHOT, timer_on_handler);
    APP_ERROR_CHECK(err_code);
    
    err_code = app_timer_create(&m_singleshot_timer_off, APP_TIMER_MODE_SINGLE_SHOT, timer_off_handler);
    APP_ERROR_CHECK(err_code);
}

void motor_on(){
  bsp_board_led_on(0);
  
  uint32_t err_code;
  cmd.conf.dgain=0;
  cmd.conf.igain=0;
  cmd.conf.linstep=0;
  cmd.conf.oc_current=2000;
  cmd.conf.pgain=8;
  cmd.conf.rpm_set=5000;
  cmd.conf.uv_voltage=10000;
  
    cmd.conf.master_stat = (1<<8);
    cmd.conf.master_stat |= MVER;
    cmd.conf.master_stat |= SET_OCUV;
    cmd.conf.master_stat &= ~SET_PID_K;
    cmd.conf.master_stat &= ~SET_PID;
    cmd.conf.master_stat |= SET_RPM_MOD;
    cmd.conf.master_stat &= ~RUN_CAL;
  
  cmd.crc=crc32_4byte((uint32_t*)&cmd.conf,sizeof(cmd.conf)); 
  
  uint8_t cmd_send_buf[sizeof(cmd)];
  memcpy((void*)&cmd_send_buf, &cmd, sizeof(cmd));

  for (int i=0;i<sizeof(cmd);i++){
    while (app_uart_put(cmd_send_buf[i]) != NRF_SUCCESS);
  }
}

void motor_off(){
  bsp_board_led_off(0);
  uint32_t err_code;
  cmd.conf.dgain=0;
  cmd.conf.igain=0;
  cmd.conf.linstep=0;
  cmd.conf.oc_current=2000;
  cmd.conf.pgain=8;
  cmd.conf.rpm_set=0;
  cmd.conf.uv_voltage=10000;
  
    cmd.conf.master_stat = (1<<8);
    cmd.conf.master_stat |= MVER;
    cmd.conf.master_stat |= SET_OCUV;
    cmd.conf.master_stat &= ~SET_PID_K;
    cmd.conf.master_stat &= ~SET_PID;
    cmd.conf.master_stat |= SET_RPM_MOD;
    cmd.conf.master_stat &= ~RUN_CAL;
  
  cmd.crc=crc32_4byte((uint32_t*)&cmd.conf,sizeof(cmd.conf));
  
  uint8_t cmd_send_buf[sizeof(cmd)];
  memcpy((void*)&cmd_send_buf, &cmd, sizeof(cmd));
  
  for (int i=0;i<sizeof(cmd);i++){
    while (app_uart_put(cmd_send_buf[i]) != NRF_SUCCESS);
  }
}

int main(void)
{   
    /* Initializing Log */
    ret_code_t err_code = NRF_LOG_INIT(NULL);
    APP_ERROR_CHECK(err_code);

    NRF_LOG_DEFAULT_BACKENDS_INIT();    
    
    NRF_LOG_INFO("HEY FROM NRF LOG!!!");

    bsp_board_init(BSP_INIT_LEDS | BSP_INIT_BUTTONS);

    const app_uart_comm_params_t comm_params =
      {
          RX_PIN_NUMBER,  
          TX_PIN_NUMBER,  
          RTS_PIN_NUMBER,
          CTS_PIN_NUMBER,
          APP_UART_FLOW_CONTROL_DISABLED,
          false,
          NRF_UART_BAUDRATE_115200
      };

    APP_UART_FIFO_INIT(&comm_params,
                         UART_RX_BUF_SIZE,
                         UART_TX_BUF_SIZE,
                         uart_event_handle,
                         APP_IRQ_PRIORITY_LOWEST,
                         err_code);

    APP_ERROR_CHECK(err_code);
 
    
    //Timer
    lfclk_request();
    create_timers();
    
    nrf_delay_ms(500);
    while(1){
      if(bsp_board_button_state_get(BSP_BOARD_BUTTON_0)){
        err_code = app_timer_start(m_singleshot_timer_on, APP_TIMER_TICKS(100), NULL);
        APP_ERROR_CHECK(err_code);
      }
      if(bsp_board_button_state_get(BSP_BOARD_BUTTON_1)){
        err_code = app_timer_start(m_singleshot_timer_off, APP_TIMER_TICKS(100), NULL);
        APP_ERROR_CHECK(err_code);
      }
      
    }
 }

[Jeff4BLE]

The nRF5x GPIO lines are undefined during reset. The solution is to use an external pull-up or pull-down resister.

[ivank4]

Forgot to mention I used a 10k resistor to pull up TX line.

[Kenneth]

Hello,

The nRF52840 Preview-DK is no longer supported or recommended to develop on, it contains early engineering samples with missing features, issues and not production tested. You should get a nRF52840 DK with the production grade samples on as soon as possible (the PDK have not been available for quite some time, so just order an nRF52840 DK from a Nordic distributor and you should get a DK).

In general I recommend pulling the nRESET pin low directly if you want to measure timing, in this case pull P0.18 directly to ground:
https://infocenter.nordicsemi.com/topic/ps_nrf52840/pin.html?cp=3_0_0_6_0 

All that said, during (pin) reset there is no guaranteed operation/behaviour. If you want to do a hardware pin reset you would only need to pull it low for >0.2us to ensure a proper reset.

Best regards,
Kenneth

[Hauser]

Same behaviour here on nRF52840 DK and our own hardware using nRF52840-CKAA-D0.

If RESET is LOW, the UART TX line is also LOW, independent of if an external pull-up is attached or not. This leads to UART framing errors on the attached host.

Any suggestions?

[Kenneth]

When reset pin is pushed the pin behavior is undefined, it may be output or floating. It is not much that can be done about this other than ensure that the pin reset is pushed for a short period of time as possible, for instance >0.2us is sufficient to ensure a hardware reset.