UART configuration and communication with an external controller

[Rohit Rajapure]

Hello Everyone,

I am developing one product using nRF52840 MCU, in this project my master controller is nRF52840 MCU and the host is STM-based MCU.

My goal is to make master and host communicate with each other using UART protocol.

So, here I referred UART peripheral example to study the same from SDK. I just simply ran the code on nRF52840 Dev-kit, And it uses default Tx and Rx pin P0.6  and P0.8. I can see that if type anything on Putty (Serial tool) it displays back.

But as my requirement, I tried to connect UART pins of nRF to the UART pin of the STM board then I am not able to print the data on putty. To get familiar with this from nRF I put data using app_uart_put() function and on the other side means STM board, I get the data using get() function and trying to put () data and display on putty similarly vice versa. But I am unable to print data.

So below attached is the code snippet that I am trying to,

if I just keep app_uart_put and write some data then it stops at the below line,

- NRF_BREAKPOINT_COND;
    // On assert the system can only recover with a reset.

main snippet,

int main(void)
{
    uint32_t err_code;

    bsp_board_init(BSP_INIT_LEDS);

    const app_uart_comm_params_t comm_params =
      {
          RX_PIN_NUMBER,
          TX_PIN_NUMBER,
          RTS_PIN_NUMBER,
          CTS_PIN_NUMBER,
          UART_HWFC,
          false,
#if defined (UART_PRESENT)
          NRF_UART_BAUDRATE_115200
#else
          NRF_UARTE_BAUDRATE_115200
#endif
      };

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

    APP_ERROR_CHECK(err_code);

#ifndef ENABLE_LOOPBACK_TEST
    printf("\r\nUART example started.\r\n");

    while (true)
    {
        uint8_t cr;
        //while (app_uart_get(&cr) != NRF_SUCCESS);
        while (app_uart_put(cr) != NRF_SUCCESS);

        if (cr == 'q' || cr == 'Q')
        {
            printf(" \r\nExit!\r\n");

            while (true)
            {
                // Do nothing.
            }
        }
    }
#else

    // This part of the example is just for testing the loopback.
    while (true)
    {
        uart_loopback_test();
    }
#endif
}

Also, with reference to the driver library, I tried to establish the same below is a snippet,

main.c file

/**
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 *
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without modification,
 * are permitted provided that the following conditions are met:
 *
 * 1. Redistributions of source code must retain the above copyright notice, this
 *    list of conditions and the following disclaimer.
 *
 * 2. Redistributions in binary form, except as embedded into a Nordic
 *    Semiconductor ASA integrated circuit in a product or a software update for
 *    such product, must reproduce the above copyright notice, this list of
 *    conditions and the following disclaimer in the documentation and/or other
 *    materials provided with the distribution.
 *
 * 3. Neither the name of Nordic Semiconductor ASA nor the names of its
 *    contributors may be used to endorse or promote products derived from this
 *    software without specific prior written permission.
 *
 * 4. This software, with or without modification, must only be used with a
 *    Nordic Semiconductor ASA integrated circuit.
 *
 * 5. Any software provided in binary form under this license must not be reverse
 *    engineered, decompiled, modified and/or disassembled.
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 * DISCLAIMED. IN NO EVENT SHALL NORDIC SEMICONDUCTOR ASA OR CONTRIBUTORS BE
 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE
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 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 *
 */
/** @file
 * @defgroup uart_example_main main.c
 * @{
 * @ingroup uart_example
 * @brief UART Example Application main file.
 *
 * This file contains the source code for a sample application using UART.
 *
 */

#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"
#if defined (UART_PRESENT)
#include "nrf_uart.h"
#endif
#if defined (UARTE_PRESENT)
#include "nrf_uarte.h"
#endif
#include "nrf_drv_uart.h"

//#define ENABLE_LOOPBACK_TEST  /**< if defined, then this example will be a loopback test, which means that TX should be connected to RX to get data loopback. */

#define MAX_TEST_DATA_BYTES     (15U)                /**< max number of test bytes to be used for tx and rx. */
#define UART_TX_BUF_SIZE 256                         /**< UART TX buffer size. */
#define UART_RX_BUF_SIZE 256                         /**< UART RX buffer size. */

//static const NRF_UART_Type *p_reg;
const nrf_drv_uart_t UART0 = NRF_DRV_UART_INSTANCE(0);

uint8_t ui8UART0Rx = 0;

void uart0_handle(nrf_drv_uart_event_t *p_event, void *p_contextr)
{
   nrf_drv_uart_rx(&UART0,&ui8UART0Rx,sizeof(ui8UART0Rx));
   nrf_drv_uart_tx(&UART0,&ui8UART0Rx,sizeof(ui8UART0Rx));
}




/**
 * @brief Function for main application entry.
 */
int main(void)
{
    uint32_t err_code;

    nrf_drv_uart_config_t uart0_cfg = NRF_DRV_UART_DEFAULT_CONFIG;
    uart0_cfg.baudrate = NRF_UART_BAUDRATE_115200;
   
//    uart0_cfg.hwfc = NRF_UART_HWFC_DISABLED;
//    uart0_cfg.interrupt_priority = 0;
//    uart0_cfg.parity = NRF_UART_PARITY_EXCLUDED;
    err_code = nrf_drv_uart_init(&UART0,&uart0_cfg,uart0_handle);
    APP_ERROR_CHECK(err_code);

    nrf_drv_uart_rx_enable(&UART0);       
}


/** @} */

sdk_config.h file for the above snippet,

// </e>

// </e>

// <e> NRFX_UARTE_ENABLED - nrfx_uarte - UARTE peripheral driver
//==========================================================
#ifndef NRFX_UARTE_ENABLED
#define NRFX_UARTE_ENABLED 0
#endif
// <o> NRFX_UARTE0_ENABLED - Enable UARTE0 instance 
#ifndef NRFX_UARTE0_ENABLED
#define NRFX_UARTE0_ENABLED 0
#endif

// <o> NRFX_UARTE1_ENABLED - Enable UARTE1 instance 
#ifndef NRFX_UARTE1_ENABLED
#define NRFX_UARTE1_ENABLED 0
#endif

// <o> NRFX_UARTE_DEFAULT_CONFIG_HWFC  - Hardware Flow Control
 
// <0=> Disabled 
// <1=> Enabled 

#ifndef NRFX_UARTE_DEFAULT_CONFIG_HWFC
#define NRFX_UARTE_DEFAULT_CONFIG_HWFC 0
#endif

// <o> NRFX_UARTE_DEFAULT_CONFIG_PARITY  - Parity
 
// <0=> Excluded 
// <14=> Included 

#ifndef NRFX_UARTE_DEFAULT_CONFIG_PARITY
#define NRFX_UARTE_DEFAULT_CONFIG_PARITY 0
#endif

// <o> NRFX_UARTE_DEFAULT_CONFIG_BAUDRATE  - Default Baudrate
 
// <323584=> 1200 baud 
// <643072=> 2400 baud 
// <1290240=> 4800 baud 
// <2576384=> 9600 baud 
// <3862528=> 14400 baud 
// <5152768=> 19200 baud 
// <7716864=> 28800 baud 
// <8388608=> 31250 baud 
// <10289152=> 38400 baud 
// <15007744=> 56000 baud 
// <15400960=> 57600 baud 
// <20615168=> 76800 baud 
// <30801920=> 115200 baud 
// <61865984=> 230400 baud 
// <67108864=> 250000 baud 
// <121634816=> 460800 baud 
// <251658240=> 921600 baud 
// <268435456=> 1000000 baud 

#ifndef NRFX_UARTE_DEFAULT_CONFIG_BAUDRATE
#define NRFX_UARTE_DEFAULT_CONFIG_BAUDRATE 30801920
#endif

// <o> NRFX_UARTE_DEFAULT_CONFIG_IRQ_PRIORITY  - Interrupt priority
 
// <0=> 0 (highest) 
// <1=> 1 
// <2=> 2 
// <3=> 3 
// <4=> 4 
// <5=> 5 
// <6=> 6 
// <7=> 7 

#ifndef NRFX_UARTE_DEFAULT_CONFIG_IRQ_PRIORITY
#define NRFX_UARTE_DEFAULT_CONFIG_IRQ_PRIORITY 6
#endif

// <e> NRFX_UARTE_CONFIG_LOG_ENABLED - Enables logging in the module.
//==========================================================
#ifndef NRFX_UARTE_CONFIG_LOG_ENABLED
#define NRFX_UARTE_CONFIG_LOG_ENABLED 0
#endif
// <o> NRFX_UARTE_CONFIG_LOG_LEVEL  - Default Severity level
 
// <0=> Off 
// <1=> Error 
// <2=> Warning 
// <3=> Info 
// <4=> Debug 

#ifndef NRFX_UARTE_CONFIG_LOG_LEVEL
#define NRFX_UARTE_CONFIG_LOG_LEVEL 3
#endif

// <o> NRFX_UARTE_CONFIG_INFO_COLOR  - ANSI escape code prefix.
 
// <0=> Default 
// <1=> Black 
// <2=> Red 
// <3=> Green 
// <4=> Yellow 
// <5=> Blue 
// <6=> Magenta 
// <7=> Cyan 
// <8=> White 

#ifndef NRFX_UARTE_CONFIG_INFO_COLOR
#define NRFX_UARTE_CONFIG_INFO_COLOR 0
#endif

// <o> NRFX_UARTE_CONFIG_DEBUG_COLOR  - ANSI escape code prefix.
 
// <0=> Default 
// <1=> Black 
// <2=> Red 
// <3=> Green 
// <4=> Yellow 
// <5=> Blue 
// <6=> Magenta 
// <7=> Cyan 
// <8=> White 

#ifndef NRFX_UARTE_CONFIG_DEBUG_COLOR
#define NRFX_UARTE_CONFIG_DEBUG_COLOR 0
#endif

// </e>

// </e>

// <e> NRFX_UART_ENABLED - nrfx_uart - UART peripheral driver
//==========================================================
#ifndef NRFX_UART_ENABLED
#define NRFX_UART_ENABLED 1
#endif
// <o> NRFX_UART0_ENABLED - Enable UART0 instance 
#ifndef NRFX_UART0_ENABLED
#define NRFX_UART0_ENABLED 1
#endif

// <o> NRFX_UART_DEFAULT_CONFIG_HWFC  - Hardware Flow Control
 
// <0=> Disabled 
// <1=> Enabled 

#ifndef NRFX_UART_DEFAULT_CONFIG_HWFC
#define NRFX_UART_DEFAULT_CONFIG_HWFC 0
#endif

// <o> NRFX_UART_DEFAULT_CONFIG_PARITY  - Parity
 
// <0=> Excluded 
// <14=> Included 

#ifndef NRFX_UART_DEFAULT_CONFIG_PARITY
#define NRFX_UART_DEFAULT_CONFIG_PARITY 0
#endif

// <o> NRFX_UART_DEFAULT_CONFIG_BAUDRATE  - Default Baudrate
 
// <323584=> 1200 baud 
// <643072=> 2400 baud 
// <1290240=> 4800 baud 
// <2576384=> 9600 baud 
// <3866624=> 14400 baud 
// <5152768=> 19200 baud 
// <7729152=> 28800 baud 
// <8388608=> 31250 baud 
// <10309632=> 38400 baud 
// <15007744=> 56000 baud 
// <15462400=> 57600 baud 
// <20615168=> 76800 baud 
// <30924800=> 115200 baud 
// <61845504=> 230400 baud 
// <67108864=> 250000 baud 
// <123695104=> 460800 baud 
// <247386112=> 921600 baud 
// <268435456=> 1000000 baud 

#ifndef NRFX_UART_DEFAULT_CONFIG_BAUDRATE
#define NRFX_UART_DEFAULT_CONFIG_BAUDRATE 30924800
#endif

// <o> NRFX_UART_DEFAULT_CONFIG_IRQ_PRIORITY  - Interrupt priority
 
// <0=> 0 (highest) 
// <1=> 1 
// <2=> 2 
// <3=> 3 
// <4=> 4 
// <5=> 5 
// <6=> 6 
// <7=> 7 

#ifndef NRFX_UART_DEFAULT_CONFIG_IRQ_PRIORITY
#define NRFX_UART_DEFAULT_CONFIG_IRQ_PRIORITY 6
#endif

// <e> NRFX_UART_CONFIG_LOG_ENABLED - Enables logging in the module.
//==========================================================
#ifndef NRFX_UART_CONFIG_LOG_ENABLED
#define NRFX_UART_CONFIG_LOG_ENABLED 0
#endif
// <o> NRFX_UART_CONFIG_LOG_LEVEL  - Default Severity level
 
// <0=> Off 
// <1=> Error 
// <2=> Warning 
// <3=> Info 
// <4=> Debug 

#ifndef NRFX_UART_CONFIG_LOG_LEVEL
#define NRFX_UART_CONFIG_LOG_LEVEL 3
#endif

// <o> NRFX_UART_CONFIG_INFO_COLOR  - ANSI escape code prefix.
 
// <0=> Default 
// <1=> Black 
// <2=> Red 
// <3=> Green 
// <4=> Yellow 
// <5=> Blue 
// <6=> Magenta 
// <7=> Cyan 
// <8=> White 

#ifndef NRFX_UART_CONFIG_INFO_COLOR
#define NRFX_UART_CONFIG_INFO_COLOR 0
#endif

// <o> NRFX_UART_CONFIG_DEBUG_COLOR  - ANSI escape code prefix.
 
// <0=> Default 
// <1=> Black 
// <2=> Red 
// <3=> Green 
// <4=> Yellow 
// <5=> Blue 
// <6=> Magenta 
// <7=> Cyan 
// <8=> White 

#ifndef NRFX_UART_CONFIG_DEBUG_COLOR
#define NRFX_UART_CONFIG_DEBUG_COLOR 0
#endif

// </e>

// </e>

// <e> UART_ENABLED - nrf_drv_uart - UART/UARTE peripheral driver - legacy layer
//==========================================================
#ifndef UART_ENABLED
#define UART_ENABLED 1
#endif
// <o> UART_DEFAULT_CONFIG_HWFC  - Hardware Flow Control
 
// <0=> Disabled 
// <1=> Enabled 

#ifndef UART_DEFAULT_CONFIG_HWFC
#define UART_DEFAULT_CONFIG_HWFC 0
#endif

// <o> UART_DEFAULT_CONFIG_PARITY  - Parity
 
// <0=> Excluded 
// <14=> Included 

#ifndef UART_DEFAULT_CONFIG_PARITY
#define UART_DEFAULT_CONFIG_PARITY 0
#endif

// <o> UART_DEFAULT_CONFIG_BAUDRATE  - Default Baudrate
 
// <323584=> 1200 baud 
// <643072=> 2400 baud 
// <1290240=> 4800 baud 
// <2576384=> 9600 baud 
// <3862528=> 14400 baud 
// <5152768=> 19200 baud 
// <7716864=> 28800 baud 
// <10289152=> 38400 baud 
// <15400960=> 57600 baud 
// <20615168=> 76800 baud 
// <30801920=> 115200 baud 
// <61865984=> 230400 baud 
// <67108864=> 250000 baud 
// <121634816=> 460800 baud 
// <251658240=> 921600 baud 
// <268435456=> 1000000 baud 

#ifndef UART_DEFAULT_CONFIG_BAUDRATE
#define UART_DEFAULT_CONFIG_BAUDRATE 30801920
#endif

// <o> UART_DEFAULT_CONFIG_IRQ_PRIORITY  - Interrupt priority
 

// <i> Priorities 0,2 (nRF51) and 0,1,4,5 (nRF52) are reserved for SoftDevice
// <0=> 0 (highest) 
// <1=> 1 
// <2=> 2 
// <3=> 3 
// <4=> 4 
// <5=> 5 
// <6=> 6 
// <7=> 7 

#ifndef UART_DEFAULT_CONFIG_IRQ_PRIORITY
#define UART_DEFAULT_CONFIG_IRQ_PRIORITY 6
#endif

// <q> UART_EASY_DMA_SUPPORT  - Driver supporting EasyDMA
 

#ifndef UART_EASY_DMA_SUPPORT
#define UART_EASY_DMA_SUPPORT 1
#endif

// <q> UART_LEGACY_SUPPORT  - Driver supporting Legacy mode
 

#ifndef UART_LEGACY_SUPPORT
#define UART_LEGACY_SUPPORT 1
#endif

// <e> UART0_ENABLED - Enable UART0 instance
//==========================================================
#ifndef UART0_ENABLED
#define UART0_ENABLED 1
#endif
// <q> UART0_CONFIG_USE_EASY_DMA  - Default setting for using EasyDMA
 

#ifndef UART0_CONFIG_USE_EASY_DMA
#define UART0_CONFIG_USE_EASY_DMA 1
#endif

// </e>

// <e> UART1_ENABLED - Enable UART1 instance
//==========================================================
#ifndef UART1_ENABLED
#define UART1_ENABLED 0
#endif
// </e>

Let me know what I did wrong here.

And also, I would perform the UART operation using other GPIO pins, can anyone suggest to me how to the configuration for this.

Thanks and Regards

Rohit R

[Vidar Berg]

Hello,

You should not have multiple transmitters on an UART bus (Putty from PC + nRF +STM) as it doesn't have any addressing mechanism. I suggest you try pin P0.26 and P0.27 (or some other GPIOs that are available) and only test the communication between the two boards. For the nRF at least, you can use RTT logging to display data received on UART.

Best regards,

Vidar

[Rohit Rajapure]

Hi Vidar,

Thank you so much for the response,

No, what I mean is after changing pins to other GPIO I would like to connect Putty (to check data) to nRF's GPIOs and STM MCU UART pins, so if any data put() from nRF, STM should receive that and if any data put() from STM, nRF should receive that and display received data on putty.

Vidar Berg said:

I suggest you try pin P0.26 and P0.27 (or some other GPIOs that are available) and only test the communication between the two boards.

- means, to use other pins we just need to give pin numbers to Tx and Rx, there is no need for any pin configuration functions. am I correct?.

Hey, I tried the pin change as per your suggestion, Now what I did is, the nRF dev-kit I directly connected the TTL board (UAB to TTL board), below is the connection and code

nRF Tx (P0.26) - TTL Rx pin

nRF Rx (P0.27) - TTL Tx pin

below is my code,

#define UART_TX_BUF_SIZE 256                         /**< UART TX buffer size. */
#define UART_RX_BUF_SIZE 256                         /**< UART RX buffer size. */

#define UART_TX_PIN   NRF_GPIO_PIN_MAP(0,26)
#define UART_RX_PIN   NRF_GPIO_PIN_MAP(0,27)


#define UART_HWFC APP_UART_FLOW_CONTROL_DISABLED

char * send_cmd = "Hello_Wellcome!";

void uart_err_handler (app_uart_evt_t *p)
{

      uint32_t i;
      for(i = 0; i < sizeof(send_cmd); i++)
      {
          while (app_uart_put(send_cmd[i]) != NRF_SUCCESS);
          
      }
}
/**
 * @brief Function for main application entry.
 */
int main(void)
{
   uint32_t err_code;

   bsp_board_init(BSP_INIT_LEDS);

   const app_uart_comm_params_t com_parm = 
   {
      UART_RX_PIN,
      UART_TX_PIN,
      RTS_PIN_NUMBER,
      CTS_PIN_NUMBER,
      UART_HWFC,
      false,
      NRF_UART_BAUDRATE_115200
   };

      APP_UART_FIFO_INIT(&com_parm,
                         UART_RX_BUF_SIZE,
                         UART_TX_BUF_SIZE,
                         uart_err_handler,
                         APP_IRQ_PRIORITY_LOWEST,
                         err_code);

    APP_ERROR_CHECK(err_code);

   while(true)
   {

   }
}

Here, I am not able to display data on TTL's putty. Unless I press any key from pc keyboard. After keypress, it starts continuously printing data on putty (that to only "Hell") did not display all data.

Can you please check the code where did I go wrong? Why it is required any key from pc keyboard?

Thanks and Regards

Rohit R

[Rohit Rajapure]

Hi Vidar,

I would like to configure the UART in freeRTOS, I am new to this, can you please guide me to configure UART in freeRTOS and execute the same.

Please the step-by-step guide to understand.

Thanks in advance

Rohit R

[Vidar Berg]

Did you succeed with getting the UART communication between the nRF and STM working? You don't necessarily have to do it differently with Freertos.

[Rohit Rajapure]

Hi Vidar,

Vidar Berg said:

Did you succeed with getting the UART communication between the nRF and STM working?

- Using USB to TTL board I am able to Put data from nRF as of now. I have removed STM as of now but it is a project requirement so I will check it as I go.

Vidar Berg said:

You don't necessarily have to do it differently with Freertos.

- I did not get this.

My end project is, I have an STM board with its host and nRF as Master, Master sends commands to Host via UART.

And this system is integrated with HVAC, so there is a wireless protocol that Openthread I am going to use to give commands using thread protocol. Here, I have a Gateway system which is also thread protocol, so If I give the command to Gateway, Gateway will send it to Master(nRF) via a wireless protocol, and then our nRF Master sends further to Host (STM) using UART protocol. So the requirement is development should be in freeRTOS.

And I am new to this freeRTOS, with no prior experience with RTOS. So it could guide how to link files and how to create tasks for GPIO interrupt, UART, and others. or any nRF examples which has GPIO interrupts task in RTOS or others. It will really help me to understand build fast.

Currently, I am going through some online videos regarding freeRTOS concepts.

Please share if any.

Thanks and Regards

Rohit R