SPIS not receiving multibyte ending with Zero value

Question

Hello there,

I'm trying to interface msp430 (master) with nrf51882 (slave) through SPI. I'm running soft device 110 to broadcast the received data from SPI through BLE. if I send any sequence of bytes not ending with Zero value, SPI and BLE work as I expected, but if the sequence of bytes ends with zero value the following if condition did not fulfill which indicating SPI transmission is not successfully completed.

if (event.evt_type == NRF_DRV_SPIS_XFER_DONE)

Here is my SPI config for nrf51822:

#define DEF_CHARACTER 0xAAu /**< SPI default character. Character clocked out in case of an ignored transaction. */

#define ORC_CHARACTER 0x55u /**< SPI over-read character. Character clocked out after an over-read of the transmit buffer. */

uint32_t spi_peripheral_init(void)

{

nrf_drv_spis_config_t spis_config = NRF_DRV_SPIS_DEFAULT_CONFIG(SPIS_INSTANCE_NUMBER);

spis_config.miso_pin = SPIS_MISO_PIN;

spis_config.mosi_pin = SPIS_MOSI_PIN;

spis_config.sck_pin = SPIS_SCLK_PIN;

spis_config.csn_pin = SPIS_CS_PIN;

spis_config.mode = NRF_DRV_SPIS_MODE_0;

/*

NRF_DRV_SPIS_MODE_0 -----> (CPOL = 0, CPHA = 0)

NRF_DRV_SPIS_MODE_1 -----> (CPOL = 0, CPHA = 1)

NRF_DRV_SPIS_MODE_2 -----> (CPOL = 1, CPHA = 0)

NRF_DRV_SPIS_MODE_3 -----> (CPOL = 1, CPHA = 1)

*/

spis_config.bit_order = NRF_DRV_SPIS_BIT_ORDER_MSB_FIRST;

spis_config.def = DEF_CHARACTER;

spis_config.orc = ORC_CHARACTER;

APP_ERROR_CHECK(nrf_drv_spis_init(&m_spis, &spis_config, spi_peripheral_event_handle));

return NRF_SUCCESS;

}

can you help me in resolving this issue and explain why the last byte in multi bit should be non zero for successful SPI transmission ?

Susheel Nuguru · Accepted Answer

I'm trying to interface msp430 (master) with nrf51882 (slave) through SPI. I'm running soft device 110 to broadcast the received data from SPI through BLE. if I send any sequence of bytes not ending with Zero value, SPI and BLE work as I expected, but if the sequence of bytes ends with zero value the following if condition did not fulfill which indicating SPI transmission is not successfully completed. 
 if (event.evt_type == NRF_DRV_SPIS_XFER_DONE) 
 That is very strange. Not sure why the last character ending with 0 have this effect on the SPI? 
 What is the character before the last char0). Probably the combination of the last two words are making SPI interpret the data as something else? What happens if you use different SPI mode on both ends?