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K22F SPI recieving 0

Question asked by Alexander Farley on Mar 1, 2017
Latest reply on Jul 20, 2017 by Alexander Farley

I'm working with an SPI barometer trying to get the K22F reading SPI responses using an SPIMaster_LDD PE component. I've scoped the bus lines - everything looks correct. K22F sends a "read address" byte, barometer then clocks out the values for the byte, then CS is set high. I'm manually driving CS to ensure that it stays low between request/read transmissions.


I've had to add a work-around for the PE SPI driver bug where the function SM1_GetBlockReceivedStatus returns before the byte is actually recieved by adding a fixed delay afterwards:


char RecieveByteSPI1()
char b, dummy;
dummy = 0;
LDD_TError er;

er = SM1_ReceiveBlock(SPI1DeviceDataPtr, &b, 1);
er = SM1_SendBlock(SPI1DeviceDataPtr, &dummy, 1);
while (!SM1_GetBlockSentStatus(SPI1DeviceDataPtr)) {
// /* Wait until data block is transmitted/received */
while (!SM1_GetBlockReceivedStatus(SPI1DeviceDataPtr)) {

return b;


Using the delay, I can see that the SPI bus transaction happens correctly at the electrical level. However, the variable b is not populated when the code returns. The SPI1 register POPR/RXDATA shows that it holds the expected value just before this function returns.


SPI1 is configured to *not* use interrupts. Aside from that, it's basically at default settings. Any idea what could be going wrong here?




1) Manually reading from POPR after receiving seems to fix the issue. Not sure why this is necessary:

b = (uint16_t)SPI_PDD_ReadPopRxFIFOReg(SPI1_BASE_PTR); /* Read character from receiver */


2) I found other reports (Is anyone really using PE Generated SPI driver with MQXLite? How? ) of PE SPI issues where GetBlockReceivedStatus wasn't working and a different flag was used to check if reception was complete. However, it looks like the receive-commplete flag is never set, and my SendByteSPI1 function hangs on this line:

while (!(SPI_PDD_GetInterruptFlags(SPI1_BASE_PTR) & SPI_SR_EOQF_MASK));//wait for the end of transfer


I just noticed this issue related to using a GPIO for CS, although I'm using a different MCU:

SPI with no CS. Problem with PE 



Edit 2017-07-11

Here are a couple of discussions on what may be the same issue:

SPI Example 


Receive FIFO Drain Flag  never getting set.