RE: nRF52840 fails to go to low-power mode when using UART RX double buffering

Sigurd — Thu, 14 Nov 2019 08:07:56 GMT

Hi,

[quote userid="84991" url="~/f/nordic-q-a/54271/nrf52840-fails-to-go-to-low-power-mode-when-using-uart-rx-double-buffering/219802"]Simple RX abort sequence (fails to return to low power mode, current is ~907uA)[/quote]

I see the same behavior, and was able to reproduce it with this code:

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/** @file
 * @defgroup Based on 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_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 UARTE_INSTANCE  0 
static const nrfx_uarte_t uarte = NRFX_UARTE_INSTANCE(UARTE_INSTANCE);  /**< UARTE instance. **/

void uarte_event_handler(nrfx_uarte_event_t const * p_event, void* p_context)
{
    uint32_t err_code;

    switch (p_event->type)
    {
        case NRFX_UARTE_EVT_TX_DONE:

            break;

        case NRFX_UARTE_EVT_RX_DONE:

            break;

        case NRFX_UARTE_EVT_ERROR:

            break;



        default:
            break;
    }
}

static uint8_t rx_buffer[1];

#define UARTE_WORKAROUND_ENABLED 1

int main(void)
{
    uint32_t err_code;

    bsp_board_init(BSP_INIT_LEDS);


    nrfx_uarte_config_t uarte_config = NRFX_UARTE_DEFAULT_CONFIG;
    uarte_config.pseltxd = TX_PIN_NUMBER;
    uarte_config.pselrxd = RX_PIN_NUMBER; 
    uarte_config.pselcts = NRF_UARTE_PSEL_DISCONNECTED;
    uarte_config.pselrts = NRF_UARTE_PSEL_DISCONNECTED;
    uarte_config.p_context = NULL;
    uarte_config.hwfc = NRF_UARTE_HWFC_DISABLED;
    uarte_config.parity = NRF_UARTE_PARITY_EXCLUDED;
    uarte_config.baudrate = NRF_UARTE_BAUDRATE_115200;
    uarte_config.interrupt_priority = NRFX_UARTE_DEFAULT_CONFIG_IRQ_PRIORITY;

    APP_ERROR_CHECK(nrfx_uarte_init(&uarte, &uarte_config, uarte_event_handler));

    nrfx_uarte_rx(&uarte, rx_buffer, 1);
    nrfx_uarte_rx_abort(&uarte);
    nrfx_uarte_uninit(&uarte);


    #if UARTE_WORKAROUND_ENABLED
    *(volatile uint32_t *)0x40002FFC = 0;
    *(volatile uint32_t *)0x40002FFC;
    *(volatile uint32_t *)0x40002FFC = 1;
    #endif // UARTE_WORKAROUND_ENABLED


    while (true)
    {
         // Wait for an event.
        __WFE();
        // Clear the internal event register.
        __SEV();
        __WFE();

    }
}


/** @} */

It might seem like the mention fix in nrfx only covers TX operation, and not RX. So the workaround mentioned by hmolesworth in the other post is still needed.

If you are using UARTE0:

    *(volatile uint32_t *)0x40002FFC = 0;
    *(volatile uint32_t *)0x40002FFC;
    *(volatile uint32_t *)0x40002FFC = 1;

For UARTE1:

*(volatile uint32_t *)0x40028FFC = 0;
*(volatile uint32_t *)0x40028FFC;
*(volatile uint32_t *)0x40028FFC = 1;

Edit:

I did some testing, and it seems like waiting for the RXTO event after RX_STOPPED is triggered is required. I will report this to the nrfx team, and the fix will hopefully make it into the upcoming nrfx v2.1 relase.

void nrfx_uarte_uninit(nrfx_uarte_t const * p_instance)
{
    uarte_control_block_t * p_cb = &m_cb[p_instance->drv_inst_idx];

    if (p_cb->handler)
    {
        interrupts_disable(p_instance);
    }
    // Make sure all transfers are finished before UARTE is disabled
    // to achieve the lowest power consumption.
    nrf_uarte_shorts_disable(p_instance->p_reg, NRF_UARTE_SHORT_ENDRX_STARTRX);
    nrf_uarte_event_clear(p_instance->p_reg, NRF_UARTE_EVENT_RXTO);
    nrf_uarte_task_trigger(p_instance->p_reg, NRF_UARTE_TASK_STOPRX);
    while (!nrf_uarte_event_check(p_instance->p_reg, NRF_UARTE_EVENT_RXTO))
    {}
    nrf_uarte_event_clear(p_instance->p_reg, NRF_UARTE_EVENT_TXSTOPPED);
    nrf_uarte_task_trigger(p_instance->p_reg, NRF_UARTE_TASK_STOPTX);
    while (!nrf_uarte_event_check(p_instance->p_reg, NRF_UARTE_EVENT_TXSTOPPED))
    {}

    nrf_uarte_disable(p_instance->p_reg);
    pins_to_default(p_instance);

#if NRFX_CHECK(NRFX_PRS_ENABLED)
    nrfx_prs_release(p_instance->p_reg);
#endif

    p_cb->state   = NRFX_DRV_STATE_UNINITIALIZED;
    p_cb->handler = NULL;
    NRFX_LOG_INFO("Instance uninitialized: %d.", p_instance->drv_inst_idx);
}

Edit2: Added a test for rx_buffer_length (Check if there is any ongoing reception)

void nrfx_uarte_uninit(nrfx_uarte_t const * p_instance)
{
    uarte_control_block_t * p_cb = &m_cb[p_instance->drv_inst_idx];

    if (p_cb->handler)
    {
        interrupts_disable(p_instance);
    }
    // Make sure all transfers are finished before UARTE is disabled
    // to achieve the lowest power consumption.
    nrf_uarte_shorts_disable(p_instance->p_reg, NRF_UARTE_SHORT_ENDRX_STARTRX);
    
    // Check if there is any ongoing reception.
    if (p_cb->rx_buffer_length)
    {
    nrf_uarte_event_clear(p_instance->p_reg, NRF_UARTE_EVENT_RXTO);
    nrf_uarte_task_trigger(p_instance->p_reg, NRF_UARTE_TASK_STOPRX);
    while (!nrf_uarte_event_check(p_instance->p_reg, NRF_UARTE_EVENT_RXTO))
    {}
    }
    
    nrf_uarte_event_clear(p_instance->p_reg, NRF_UARTE_EVENT_TXSTOPPED);
    nrf_uarte_task_trigger(p_instance->p_reg, NRF_UARTE_TASK_STOPTX);
    while (!nrf_uarte_event_check(p_instance->p_reg, NRF_UARTE_EVENT_TXSTOPPED))
    {}

    nrf_uarte_disable(p_instance->p_reg);
    pins_to_default(p_instance);

#if NRFX_CHECK(NRFX_PRS_ENABLED)
    nrfx_prs_release(p_instance->p_reg);
#endif

    p_cb->state   = NRFX_DRV_STATE_UNINITIALIZED;
    p_cb->handler = NULL;
    NRFX_LOG_INFO("Instance uninitialized: %d.", p_instance->drv_inst_idx);
}

RE: nRF52840 fails to go to low-power mode when using UART RX double buffering

Robert Hutchinson — Wed, 13 Nov 2019 06:47:39 GMT

Hi Sigurd,

Further to the findings above, it seems that we are unable to abort from a RX transfer and successfully return to a low-power state (refer to the sequence below). It effectively means that only after the number of bytes configured by nrfx_uarte_rx() have been received can we successfully uninitialize the peripheral, which is simple but significant problem.

Simple RX abort sequence (fails to return to low power mode, current is ~907uA)

nrfx_uarte_init(&diag_uarte_instance, &uarte_config, uarte_event_handler);
nrfx_uarte_rx(&diag_uarte_instance, &rx0, 1);
nrfx_uarte_rx_abort(&diag_uarte_instance);
nrfx_uarte_uninit(&diag_uarte_instance);

Note that we have tested this with SDK v16.0.0. Could you please let us know if there is something we're doing wrong here?

Best regards,

Rob

RE: nRF52840 fails to go to low-power mode when using UART RX double buffering

Robert Hutchinson — Wed, 13 Nov 2019 00:33:38 GMT

Hi Sigurd,

Thanks for your help and suggestion.

We have updated to the latest SDK v16.0.0, which has nrfx v1.8.0, however the problem is still present.

I believe the UART changes in v1.7.2 were actually something we had experienced previously and had been working around by nrfx_uarte_tx_abort after sending over UART. However, the changes do not seem to help us on the receive side, as described above.

If you have any further pointers or could clarify the usage of double buffering on RX transfers that would be great.

Best regards,

Rob

RE: nRF52840 fails to go to low-power mode when using UART RX double buffering

Sigurd — Tue, 12 Nov 2019 15:33:51 GMT

Hi,

Please try to update to latest nrfx driver, and see it that solves the issue. There was a bug-fixe when it comes to gracefully uinit of the UARTE peripheral in nrfx v1.7.2. See e.g. this post on this topic.