SPI communication problem

[Alan Klimala]

Hello

I'm using NRF52 PCA10040 board., SDK 15.2 libraries with GNU ARM GCC and Eclipse as an IDE developing FW on Windows10 x64.

I have been facing a problem trying to service external SPI flash memory (AT25SF041, but not only - you can read about it further). I'm not able to read memory ID registers. More precisely I got incorrect response from the memory.

I was trying few memory chips from different vendors with the same result. I have no such a problem using STM32L0 MCU. What is more interesting, I have been investigating SPI communication at electric signal level using DSO and both communication (using NRF52 and STm32) looks exactly the same with the difference that memory responds to ID request got from SMT32 with appropriate device ID data but on NRF52 request it sends incorrect response.

Has anyone ever met such a strange problem?

Here is the low-level code I've written for AT25SF041 driver:

#include "nrf_gpio.h"
#include "nrfx_spi.h"
 
#include "logger.h"
 
#define CS_PIN          28
#define SCK_PIN         29
#define MISO_PIN        30
#define MOSI_PIN        31
 
 
static const nrfx_spi_t _xSpiHandler = NRFX_SPI_INSTANCE(0);
static nrfx_spi_config_t _xSpiConfig = NRFX_SPI_DEFAULT_CONFIG;
 
static uint8_t _bIsInitialized = 0;
static volatile uint8_t _bTransferFinished;
 
static void prvvSpiEventHandler(nrfx_spi_evt_t const* aEvent, void* aContext)
{
    _bTransferFinished = 1;
}
 
void AT25SF041_vInitializeLL()
{
    if (_bIsInitialized)
    {
        return;
    }
 
    /** Set SPI pins n the configuration object and initialize interface. */
    _xSpiConfig.miso_pin = MISO_PIN;
    _xSpiConfig.mosi_pin = MOSI_PIN;
    _xSpiConfig.sck_pin = SCK_PIN;
    _xSpiConfig.ss_pin = NRFX_SPI_PIN_NOT_USED;
    _xSpiConfig.frequency = NRF_SPI_FREQ_125K ;
    _xSpiConfig.mode = NRF_SPI_MODE_0;
    nrfx_spi_init(&_xSpiHandler, &_xSpiConfig, &prvvSpiEventHandler, NULL);
 
    /** Prepare CS pin and set its state to HGH. */
    nrf_gpio_cfg_output(CS_PIN);
    nrf_gpio_pin_set(CS_PIN);
 
    _bIsInitialized = 1;
}
 
void AT25SF041_vSetCSActiveLL()
{
    nrf_gpio_pin_clear(CS_PIN);
}
 
void AT25SF041_vSetCSInactiveLL()
{
    nrf_gpio_pin_set(CS_PIN);
}
 
int8_t AT25SF041_bXferBytesLL(uint8_t* aTxBuf, uint8_t aTxLen, uint8_t* aRxBuf, uint8_t aRxLen)
{
    nrfx_spi_xfer_desc_t xferDesc = NRFX_SPI_XFER_TRX(aTxBuf, aTxLen, aRxBuf, aRxLen);
 
    AT25SF041_vSetCSActiveLL();
 
    _bTransferFinished = 0;
 
    nrfx_err_t error = nrfx_spi_xfer(&_xSpiHandler, &xferDesc, 0);
    if (error != NRFX_SUCCESS)
    {
        return -1;
    }
 
    while (!_bTransferFinished)
    {
    }
 
    AT25SF041_vSetCSInactiveLL();
 
    return 0;
}

[Jørgen Holmefjord]

Hi,

What ID are you reading, and what do you expect? What parameters do you pass to the function AT25SF041_bXferBytesLL() when you want to read the ID?

Best regards,
Jørgen

[Jørgen Holmefjord]

It looks like you are writing more bytes than necessary. If you want to write a single byte and receive 3 bytes after this, I would recommend using the following code:

uint8_t txBuf[] =
{
	0x9F
};

uint8_t rxBuf[4] = { 0 };

AT25SF041_bXferBytesLL(txBuf, 1, rxBuf, 4);

The peripheral will send out "dummy bytes" to read the following bytes into the RX buffer, you just need to ignore the byte received while transmitting the first byte.

[Alan Klimala]

Hi  Jørgen,
Unfortunatelly the result is exactly the same. Take a look on a screenshot below:

[Jørgen Holmefjord]

Can you try changing the NRFX_SPIM_MISO_PULL_CFG in sdk_config.h? It is strange that the device does not respond with the same output when it receive the same command on MOSI line.

[Alan Klimala]

Sorry for late answer, I wasn't at office last two days. I tested all options but communication is still wrong. The only change is the response, but it might be connected to the fact that I switched tfrom nrfx_spi to nrfx_spim driver. Please take a look at screenshots below.

1. With NRF_GPIO_PIN_NOPULL

2. With NRF_GPIO_PIN_PULLDOWN

3. With NRF_GPIO_PIN_PULLUP