nrf_spi_mngr_perform Keeps MISO Line Low

[aa]

Hi,

I'm working with the nrf52840 and spi mngr to talk to a SPI flash memory (AT25SF081). I use nrf_spi_mngr_perform to send a command to read the manufacturer ID

const uint8_t data[] = {0x9F};
uint8_t mnf_id[4] = {0x00, 0x00, 0x00, 0x00};
nrf_spi_mngr_transfer_t const transfer[] =
  {
    NRF_SPI_MNGR_TRANSFER(data, sizeof(data), response, sizeof(response))
  };

nrf_spi_mngr_perform(&m_nrf_spi_mngr, NULL, transfer, ARRAY_SIZE(transfer), NULL);

The device should reply with a known code {0x1F, 0x85, 0x01}, but instead I'm getting only the first and last byte: 0x1F, 0x00, 0x01

After a lot of debugging I discovered that If I disconnect the MISO line from the nRF52840-DK board, the correct sequence is actually being sent by the memory, which proves the app is the one

driving the line down just during the 2nd byte:

I already tried setting the NRFX_SPI_MISO_PULL_CFG flag to 3 (MISO pullup) and 0 (MISO no pull) without success (besides the line remaining high - when CFG = 3 - permanently when the transaction finishes.

I also tried changing the irq_priority during the configuration and also via SPI_DEFAULT_CONFIG_IRQ_PRIORITY without any success. This is my config:

static nrf_drv_spi_config_t const m_master_config =
{
	.sck_pin        = NRF_GPIO_PIN_MAP(1, 4),
	.mosi_pin       = NRF_GPIO_PIN_MAP(1, 1),
	.miso_pin       = NRF_GPIO_PIN_MAP(1, 2),
	.ss_pin         = NRF_GPIO_PIN_MAP(1, 3),			
	.irq_priority   = APP_IRQ_PRIORITY_LOWEST,
	.orc            = 0x00,
	.frequency      = NRF_DRV_SPI_FREQ_2M,
	.mode           = NRF_DRV_SPI_MODE_0,			
	.bit_order      = NRF_DRV_SPI_BIT_ORDER_MSB_FIRST
};

Thinking the problem was caused by initialising the module at the wrong time, I also tried calling it via app_sched_event_put(), but got the same results.

Am I doing something obviously wrong? Any advice would be greatly appreciated.

I'm using the SDK v15.3.0.

Thanks.

A.

[aa]

haakonsh, thanks heaps for the advice; I can confirm that adding a 100ohm series resistor in the MISO line solves the problem! I was convinced the lines were noise-free.