Is Errata 109 occurrence related to SPI frequency?

[Kyle Krueger]

I have been having issues with our Flash component (S25FL256S) over SPI with the nRF52832 using easyDMA. When reading out values of a peripheral, the returned contents are sometimes empty. This has been seen very often when using a low SPI frequency (256 kHz), and much less frequently at 8 MHz.

We init the flash with the nrf_drv_spi abstraction layer.

nrf_gpio_cfg_output( FLASHMEM_CS );
nrf_gpio_pin_set( FLASHMEM_CS );

nrf_delay_ms( 100 );

nrf_drv_spi_config_t spi_config = NRF_DRV_SPI_DEFAULT_CONFIG;

spi_config.ss_pin   = FLASHMEM_CS;
spi_config.miso_pin = FLASHMEM_SDO;
spi_config.mosi_pin = FLASHMEM_SDI;
spi_config.sck_pin  = FLASHMEM_SCK;
spi_config.frequency = NRF_DRV_SPI_FREQ_8M;

spi_config.irq_priority = SPI_DEFAULT_CONFIG_IRQ_PRIORITY;

spi_config.bit_order = NRF_SPI_BIT_ORDER_MSB_FIRST;
spi_config.mode = NRF_SPI_MODE_0;  //CPHA = 0 CPOL = 0
LOG_FLASH( "Trying to init SPI\n" );
ret_code_t ret_code =  nrf_drv_spi_init( &spi, &spi_config, spi_event_handler, NULL /* p_context  */ );
LOG_FLASH( "nrf_drv_spi_init - ret_code %d\n", ret_code );
APP_ERROR_CHECK( ret_code );

and are making our spi calls through a function to abstrtact the nrf_drv_spi_transfer command

static bool spiXfer( spi_cmd_t * spiCmd ) {
    uint32_t rxLength = 0;
    ret_code_t ret_code;

    // if queue empty, return
    if ( spiCmd == &CUSTOM__EMPTY_SPI_CMD) return true;

    memset( spi_rx_buf, 0, CUSTOM__SPI_BFF_SIZE );

    logSpiCmdDetails(spiCmd);

    // nordic uses a shift buffer, rx must be length of tx+rx
    if(spiCmd->rxLength){
        rxLength += spiCmd->txLength;
        rxLength += spiCmd->rxLength;
    }

    ret_code = nrf_drv_spi_transfer( &spi,
                                     spiCmd->txData,
                                     spiCmd->txLength,
                                     spi_rx_buf,
                                     rxLength );

    APP_ERROR_CHECK( ret_code );
    return((ret_code == 0) ? true : false);
}

the values being passed into this function have been confirmed as correct.

Since this issue has a similar symptom of Errata 109, I was wondering if it could be related.

In this case, enabling the Errata 109 workaround is having no effect on the results.

[Kyle Krueger]

The receive buffer has a default callback, which manages a queue of SPI commands. Read commands are provided with additional nested function pointers to read out the data (ex. memcopy). This nested function pointer is the last part of the default callback.

At the beginning of each function which uses spiXfer first check a spiBusy flag, if this is true, the command will be ignored, and an error code is returned (to manage a retry). If it is not true, we write true, and proceed to send the command. It will only be marked to false again after the default SPI callback inclusive of the nested function pointer finishes with or without an error.