nRF5340 SPI slave doesnt seem to receive

Question

Hi, 
 I have ported my already working nRF52840 SPI slave code to a nRF5340, but it doesnt seem to receive any data. I have verified the CS, SCK and MOSI signals, but no MISO from nRF5340. 
 .
.
static const struct spi_config spis_cfg = {
	.operation = SPI_WORD_SET(8) | SPI_TRANSFER_MSB | SPI_OP_MODE_SLAVE | SPI_MODE_CPOL | SPI_MODE_CPHA,
	.slave = 1,
};
.
.
static void spi_slave_init(void)
{
	spis_dev = DEVICE_DT_GET(MY_SPI_SLAVE);
	
	if (!device_is_ready(spis_dev)) {
 printk("SPI slave device not ready!
");
	}
	else
 LOG_INF ("SPI slave ready");
}
.
.
static int spi_slave_check_for_message(void)
{
	int signaled, result;

k_poll_signal_check(&spi_slave_done_sig, &signaled, &result);
	
	if (signaled != 0){
 slave_tx_buffer [0] = 0x01;	// init slave tx buffer
 return 0;
	}
	
	else return -1;
}
.
.
static int spi_slave_wait_msg(uint8_t txlen, uint8_t rxlen)
{
	const struct spi_buf s_tx_buf = {
 .buf = slave_tx_buffer,
 .len = txlen 
	};
	const struct spi_buf_set s_tx = {
 .buffers = &s_tx_buf,
 .count = 1
	};

struct spi_buf s_rx_buf = {
 .buf = slave_rx_buffer,
 .len = rxlen
	};
	const struct spi_buf_set s_rx = {
 .buffers = &s_rx_buf,
 .count = 1
	};

// Reset signal - this flag the next msg check 
	k_poll_signal_reset(&spi_slave_done_sig);
	
	// Start transaction
	int error = spi_transceive_signal(spis_dev, &spis_cfg, &s_tx, &s_rx, &spi_slave_done_sig);	// once a cycle is complete, the 'spi_slave_done_sig' will get signelled

if(error != 0){
 LOG_ERR("SPI slave transceive error: %i
", error);
 return error;
	}
	
	return 0;
}
.
.
static void spis_handler (struct k_work *item) {

static uint8_t txlen, rxlen;
int8_t i=0, loopCnt=0;
static uint8_t startRec=0;
uint16_t hostFWRev;

if (spi_slave_check_for_message() == 0){
 
 LOG_INF ("---- Received SPI msg -----");

switch (slave_rx_buffer [0]) {
 case 'V':	// Feature 7
 hostFWRev = EncVerString ();
 LOG_INF ("Host radio FW : %04x", hostFWRev);
 
 slave_tx_buffer[0] = 'A';
 slave_tx_buffer[1] = (uint8_t)(hostFWRev >> 8);
 slave_tx_buffer[2] = (uint8_t)(hostFWRev & 0x00ff);
 txlen = 3;
 rxlen = 1;
 break;

case 'A':	// ACK/NAK request. This is the second byte send by host after the command. Only thing we need is to send the ACK/NAK of last command
 //LOG_INF ("ACK/NAK command");
 break;

default :
 LOG_ERR ("default %x, %c", slave_rx_buffer [0], slave_rx_buffer [0]);
 slave_tx_buffer[0] = 'K';
 txlen = 1;
 rxlen = 1;
 }
 // Prepare the next SPI slave transaction - this means the ACK/NAK doesnt get send immediately, but in next rx cycle. 
 // This means we have to either send same command twice or have a ACK/NAK request command, which is send after each command
 spi_slave_wait_msg(txlen, rxlen);	
	}

k_msleep (1);
	k_work_submit (item);
}
.
.
void main(void)
{
.
.
 k_poll_signal_reset(&spi_slave_done_sig);
	spi_slave_init ();
	spi_slave_wait_msg (1, 1);	// this starts the k_poll event to wait for next spi rx

k_work_init(&spis_work, spis_handler); // spis handling is done in system queue to avoid issues with spi async transfers
	k_work_submit (&spis_work);
	.
	.
} 
 I get 'SPI slave ready' as a result of invoking spi_slave_init () function. 
 I can see the spis_handler () is invoked repeatedly, but ' spi_slave_check_for_message () == 0 ' seems to fail all the time. 
 I use nordic SDK 2.9.0. 
 
 I saw in the nRF5340 user guide that there is a hardware semaphore for accessing spi buffers, which was not available in nRF52840. Is there anything I need to implement in the application level to do that? 
 
 I have tried all I can think of and need some help urgently. 
 
 Thanks, 
 Kaushalya

nRF5340 SPI slave doesnt seem to receive

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