Cannot initialize QSPI (nRF52840 and Micron NOR Flash)

Question

I'm working on a custom board with a nRF52840 and a Micron NOR Flash MT25QU128ABA8E12-0SIT (https://www.micron.com/products/nor-flash/serial-nor-flash/part-catalog/mt25qu128aba8e12-0sit)

I copied code from the QSPI example in SDK17.1.0, after verifying that it worked on the PCA10056 board.

Here's a snippet of the relevant code

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include "boards.h"
#include "app_util_platform.h"
#include "app_error.h"
#include "boards.h"

#include "nrf_drv_qspi.h"
#include "nrf_delay.h"

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

#include "main_memory.h"

#define QSPI_STD_CMD_WRSR   0x01
#define QSPI_STD_CMD_RSTEN  0x66
#define QSPI_STD_CMD_RST    0x99

#define QSPI_TEST_DATA_SIZE 256

#define WAIT_FOR_PERIPH() do { \
        while (!m_finished) {} \
        m_finished = false;    \
    } while (0)

static volatile bool m_finished = false;
static uint8_t m_buffer_tx[QSPI_TEST_DATA_SIZE];
static uint8_t m_buffer_rx[QSPI_TEST_DATA_SIZE];

static void qspi_handler(nrf_drv_qspi_evt_t event, void * p_context);
static void configure_memory(void);

void main_memory_setup(void){ }
void main_memory_start(void){ }

void main_memory_tests(void)
{ 
    uint32_t i;
    uint32_t err_code;

    err_code = NRF_LOG_INIT(NULL);
    APP_ERROR_CHECK(err_code);

    NRF_LOG_INFO(""
                 "QSPI write and read example using 24bit addressing mode");

    srand(0);
    for (i = 0; i < QSPI_TEST_DATA_SIZE; ++i)
    {
        m_buffer_tx[i] = (uint8_t)rand();
    }

    nrf_drv_qspi_config_t config = NRF_DRV_QSPI_DEFAULT_CONFIG;

    err_code = nrf_drv_qspi_init(&config, qspi_handler, NULL);
    APP_ERROR_CHECK(err_code);
    NRF_LOG_INFO("QSPI example started.");
}

I checked multiple times that all the GPIO pins are properly defined, as below

//QSPI
#define BSP_QSPI_CSN_PIN          P0_18
#define BSP_QSPI_SCK_PIN          P0_19
#define BSP_QSPI_IO0_PIN          P0_21
#define BSP_QSPI_IO1_PIN          P0_22
#define BSP_QSPI_IO2_PIN          P0_23
#define BSP_QSPI_IO3_PIN          P1_00

And I copied the relevant sections from the example's sdk_config.h

As soon as I call nrf_drv_qspi_init(&config, qspi_handler, NULL);, I get an APP_ERROR_CHECK of a timeout.

Everything I read, implies a physical connection problem on the board between the nRF52 and the QSPI NOR Flash. But following the traces, everything looks as it should be. I could assume a poor BGA soldering or other chip-specific problem, but it happens on 5 different boards, so I can rule that out.

I cannot use the logic analyzer, given it's a multilayer board and the QSPI chip is a BGA form factor (not saying i cannot be done, just that I don't have the tools/skills to do it).

I looked at everything I could think of (pin drive strength, etc) and tried different clock cycles and configs (i.e. QSPI_CONFIG_READOC 2), but nothing makes a difference

I'm obviously missing something, possibly in the timing of the Micron part we are using. I could understand if the code failed when trying to read or write to the NOR, but in the case fails at init, which seems to imply a pretty major problem

Any suggestions on what to try next? What am I missing?

EDIT: i just noticed that the board designer has used P0.18 as CS, and CS can be defined as nRESET. I managed to read the voltage on the QSPI_CSN (P0.18), and it's always stuck high. I found a ticket mentioning removing CONFIG_GPIO_AS_PINRESET, which I did, but doesn't seem to make any differenbce even after forcing a clean rebuild

Any idea why P0.18 is stuck high (assuming it's not a hardware problem, but the board layout seems ok, and it happens on multiple boards)

robca · Accepted Answer

Answering my own question: it was indeed a problem with having originally defined CONFIG_GPIO_AS_PINRESET. Once that is done, the pin is always pulled up high and even if redefined as a GPIO or for QSPI, it won't work (with no error notification) 
 What I didn't realize, is that the setting is persisted in UICR (which makes sense in hindsight, as most things do ). So once an image with CONFIG_GPIO_AS_PINRESET is flashed on the chip, pin P0.18 will not work for anything else anymore, until the UICR data is erased 
 So, after removing CONFIG_GPIO_AS_PINRESET, I also needed to erase UICR, either with nrfjprog or the Erase All function in the GUI Nordic Prgrammer. 
 Problem solved, QSPI now initializes as expected

Cannot initialize QSPI (nRF52840 and Micron NOR Flash)

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