UARTE data loss on nRF52832 and nRF52840 when using EasyDMA

Question

I'm trying to read data over UART as fast as possible using the double-buffering feature and EasyDMA, but even this simple example I've posted is losing data.

I've set up three buffers:

Active - the one EasyDMA is writing into.
Next - next buffer EasyDMA should write to.
Ready - buffer with data for the application to consume.

And this is the flow:

The Active buffer is loaded into EasyDMA in the initialization function.
The ENDRX_STARTRX short is set for continuous reception.
On the event RXSTARTED I set the Next buffer in EasyDMA, which should now hold two buffers.
On the event ENDRX the Next buffer becomes the Active buffer because of the double buffering. I re-arm the EasyDMA using the old Ready buffer (which then becomes Next) and the old Active buffer (with data) becomes the Ready buffer.

When I send 1 byte at a time I can see through the debugger that everything works as expected, data is stored in the buffers and the UARTE module swaps out the buffers as told. However, if I dump a couple of hundred of bytes at a time I can see from the "counter" variable that I'm losing data and even when dumping the same amount of data repeatedly I can see from the "counter" that the data loss is inconsistent.

I've tested this on both the nRF52832 and nRF52840 development kits using SDK 14.2.

What am I doing wrong here?

#include <stdbool.h>
#include <stdint.h>
#include "nrf_delay.h"
#include "boards.h"

#include "nrf_uarte.h"
#include "nrf_drv_common.h"
#include "app_util_platform.h"

#define BUFFER_SIZE         32
#define NUMBER_OF_BANKS     3
#define ACTIVE_BANK_OFFSET  0
#define NEXT_BANK_OFFSET    1
#define READY_BANK_OFFSET   2
#define TX_PIN              TX_PIN_NUMBER
#define RX_PIN              RX_PIN_NUMBER

static uint8_t buffer[NUMBER_OF_BANKS][BUFFER_SIZE];
static uint32_t counter = 0;
static uint32_t active_bank = 0;

void UARTE0_UART0_IRQHandler(void)
{
    if (nrf_uarte_event_check(NRF_UARTE0, NRF_UARTE_EVENT_RXSTARTED))
    {
        nrf_uarte_event_clear(NRF_UARTE0, NRF_UARTE_EVENT_RXSTARTED);

        uint8_t next_bank = (active_bank + NEXT_BANK_OFFSET) % NUMBER_OF_BANKS;

        nrf_uarte_rx_buffer_set(NRF_UARTE0, buffer[next_bank], BUFFER_SIZE);
    }

    if (nrf_uarte_event_check(NRF_UARTE0, NRF_UARTE_EVENT_ENDRX))
    {
        nrf_uarte_event_clear(NRF_UARTE0, NRF_UARTE_EVENT_ENDRX);

        active_bank++;

        if (active_bank >= NUMBER_OF_BANKS) 
        {
            active_bank = 0;
        }

        counter++;
    }

    if (nrf_uarte_event_check(NRF_UARTE0, NRF_UARTE_EVENT_ERROR))
    {
        nrf_uarte_event_clear(NRF_UARTE0, NRF_UARTE_EVENT_ERROR);

        uint32_t code = nrf_uarte_errorsrc_get_and_clear(NRF_UARTE0);
    }
}

void init(void)
{
    nrf_gpio_pin_set(TX_PIN);
    nrf_gpio_cfg_output(TX_PIN);
    nrf_gpio_cfg_input(RX_PIN, NRF_GPIO_PIN_NOPULL);

    nrf_uarte_txrx_pins_set(NRF_UARTE0, TX_PIN, RX_PIN);

    nrf_uarte_configure(NRF_UARTE0, NRF_UARTE_PARITY_EXCLUDED, NRF_UARTE_HWFC_DISABLED);

    nrf_uarte_baudrate_set(NRF_UARTE0, NRF_UARTE_BAUDRATE_115200);

    nrf_uarte_event_clear(NRF_UARTE0, NRF_UARTE_EVENT_RXSTARTED);
    nrf_uarte_event_clear(NRF_UARTE0, NRF_UARTE_EVENT_ERROR);
    nrf_uarte_event_clear(NRF_UARTE0, NRF_UARTE_EVENT_ENDRX);

    nrf_uarte_int_enable(NRF_UARTE0,
                         NRF_UARTE_INT_RXSTARTED_MASK |
                         NRF_UARTE_INT_ERROR_MASK     |
                         NRF_UARTE_INT_ENDRX_MASK);

    nrf_uarte_shorts_enable(NRF_UARTE0, NRF_UARTE_SHORT_ENDRX_STARTRX);

    nrf_drv_common_irq_enable(UART0_IRQn, APP_IRQ_PRIORITY_HIGHEST);

    nrf_uarte_enable(NRF_UARTE0);

    nrf_uarte_rx_buffer_set(NRF_UARTE0, buffer[0], BUFFER_SIZE);

    nrf_uarte_task_trigger(NRF_UARTE0, NRF_UARTE_TASK_STARTRX);
}


int main(void)
{
    init();

    for (;;)
    {
        __WFI();
    }
}

Edit: changed header include in example code and changed pin names.

Edvin · Accepted Answer

Hello, 
 I have tried to send 31 * 32 bytes via my uart terminal (maximum allowed transmission by the terminal), and I can't seem to replicate your problem. 
 I tried to add to your code: 
 ...
 counter++;
 if(counter >=31)
 {
 counter = 0;
 } 
 And it always stops on the breakpoint I placed there after I send the packet. I can also see in the buffers that the data is aligned with the end of the data that I send, so it indicates that I don't loose any data. I have tested it quite a few times. Do you get data loss often? I tried to send 31*32 (=992) bytes about 20 times in a row, and the breakpoint always fired. 
 Have you configured the sdk_config.h file, or in some other way possibly changed to use the RC Oscillator instead of the crystal? Have you tried to check the RX pin with e.g. a logic analyzer to see if all the data is sent correctly? What device are you sending the UART data from? 
 
 Best regards, 
 Edvin

UARTE data loss on nRF52832 and nRF52840 when using EasyDMA

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