Why is CS pulled high before LPSPI has finished transmitting?

[kalvin]

void SPI_Init(LPSPI_Type *instance,SpiSpeedType Speed)
{
instance->IER = 0x00000000; /* Interrupts not used */
instance->DER = 0x00000000; /* DMA not used */
instance->CFGR0 = 0x00000000; /* Defaults: */
/* RDM0=0: rec'd data to FIFO as normal */
/* CIRFIFO=0; Circular FIFO is disabled */
/* HRSEL, HRPOL, HREN=0: Host request disabled */
instance->CFGR1 = LPSPI_CFGR1_MASTER(1); /* Configurations: master mode */
/* PCSCFG=0: PCS[3:2] are enabled */
/* OUTCFG=0: Output data retains last value when CS negated */
/* PINCFG=0: SIN is input, SOUT is output */
/* MATCFG=0: Match disabled */
/* PCSPOL=0: PCS is active low */
/* NOSTALL=0: Stall if Tx FIFO empty or Rx FIFO full */
/* AUTOPCS=0: does not apply for master mode */
/* SAMPLE=0: input data sampled on SCK edge */
/* MASTER=1: Master mode */

instance->TCR |= LPSPI_TCR_PRESCALE(SpiSpeed.prescale)| /* PRESCALE=2: Functional clock divided by 40M/2 = 20M */
LPSPI_TCR_PCS(2) |
LPSPI_TCR_FRAMESZ(7); /* FRAMESZ=7: # bits in frame = 7+1=8 */

instance->CCR |= LPSPI_CCR_SCKDIV(SpiSpeed.sckdiv) | /* 20/(8+2) = 2M */
LPSPI_CCR_DBT(8) |
LPSPI_CCR_SCKPCS(4) |
LPSPI_CCR_PCSSCK(4);

instance->FCR = LPSPI_FCR_TXWATER(3); /* RXWATER=0: Rx flags set when Rx FIFO >0 */
/* TXWATER=3: Tx flags set when Tx FIFO <= 3 */
instance->CR = LPSPI_CR_MEN_MASK
|LPSPI_CR_DBGEN_MASK; /* Enable module for operation */
/* DBGEN=1: module enabled in debug mode */
/* DOZEN=0: module enabled in Doze mode */
/* RST=0: Master logic not reset */
/* MEN=1: Module is enabled */
}
uint8_t LPSPI_ReadWriteByte(LPSPI_Type *instance,uint8_t byte)
{
uint8_t recieve = 0;

while((instance->SR & LPSPI_SR_TDF_MASK)>>LPSPI_SR_TDF_SHIFT==0);
/* Wait for Tx FIFO available */
instance->TDR = byte; /* Transmit data */
instance->SR |= LPSPI_SR_TDF_MASK; /* Clear TDF flag */

while((instance->SR & LPSPI_SR_RDF_MASK)>>LPSPI_SR_RDF_SHIFT==0);
/* Wait at least one RxFIFO entry */
recieve= instance->RDR; /* Read received data */
instance->SR |= LPSPI_SR_RDF_MASK; /* Clear RDF flag */

return recieve; /* Return received data */
}

[davidtosenovjan · Accepted solution]

It is given by following bits in Transmit Command Register (TCR):

[kalvin]

 @davidtosenovjan thanks for your answer,but why there are three bytes before each byte is 0x00, please see the picture in the attachment .

[davidtosenovjan]

Why you are transmitting per four bytes when the function seems to be written per byte? Which data you are transmitting, it is not apparent from your code snippet.

[kalvin]

 @davidtosenovjan  The null byte problem has been solved, but I still have a question to ask, why does CS keep low level after TCD CONC is enabled? Please see the attached picture .

[davidtosenovjan]

Here you may read description to understand how to set CONT/CONTC bits:

https://community.nxp.com/t5/S32K/S32K14x-Command-Word-in-LPSPI/td-p/1040779

[kalvin]

Thanks @davidtosenovjan  my problem has been solved ！

[kalvin]

transmit buffer is ：

spi_buffer_t master_buffer =
{
.tx = {0xA,0xB,0xC,0xD,0xE,0xF,0x9,0x8,0x7,0x6,0x5,0x4,0x3,0x2,0x1,0xAA},
.rx = {0}
};