WEBENCH® Tools/CC2640R2F: SPI read fail

Hi dsp999,

Please follow the instructions from the SPI.h TI Driver Runtime API and the spimaster example.  You may need to further configure the handshake and frame format settings, furthermore the sensor you are using may have additional communication requirements as described in its datasheet.  If you send buffer bytes to further actuate the SPI clock then does the sensor ever transmit data?

Regards,
Ryan

You set masterTransaction.count = 2 and it is correct to see only two clock bytes.

if I set masterTransaction.count = 3,  it will send 3 bytes, not send 2 bytes and then read, right?

in ohter words, how does it know how many bytes to send and how many to read? 

I suppose you should refer to datasheet of your SPI slave device to know how many bytes to read or write.

you don't get my question.

I definitely know, upon the spec, there should send 2 bytes (from CC2640) and get 1 byte response from sensor.

 how to set the parameter of the transaction? there is only one count parameter!

In such case, you should set count to 3.

I have read carefully the documents, and it is still the understanding and the question the same.   

the core code of the document and sample is :

/* Copy message to transmit buffer */
strncpy((char *) masterTxBuffer, MASTER_MSG, SPI_MSG_LENGTH);

for (i = 0; i < MAX_LOOP; i++) {
/*
* Wait until slave is ready for transfer; slave will pull
* Board_SPI_SLAVE_READY low.
*/
sem_wait(&masterSem);

/* Initialize master SPI transaction structure */
masterTxBuffer[sizeof(MASTER_MSG) - 1] = (i % 10) + '0';
memset((void *) masterRxBuffer, 0, SPI_MSG_LENGTH);
transaction.count = SPI_MSG_LENGTH;
transaction.txBuf = (void *) masterTxBuffer;
transaction.rxBuf = (void *) masterRxBuffer;

/* Perform SPI transfer */
transferOK = SPI_transfer(masterSpi, &transaction);
if (transferOK) {
Display_printf(display, 0, 0, "Master received: %s", masterRxBuffer);
}
else {
Display_printf(display, 0, 0, "Unsuccessful master SPI transfer");
}

}

you see there is only one parameter:   transaction.count = SPI_MSG_LENGTH;

how the transaction know how many bytes should there be from the spi slave?

the spi master must generate the clk for spi bus, either write or read, right?

The spi master would generate number of byte pulse according to transaction.count. It's responsibility of  application to count total number of write and read bytes.

can not figure out how "It's responsibility of  application to count total number of write and read bytes."

here the case we need to write 2 bytes and then get 1 byte back (read), how to set the  count parameter? 2 or 3?

dsp999 said:

here the case we need to write 2 bytes and then get 1 byte back (read), how to set the  count parameter? 2 or 3?

For your case think need to:

• Set masterTransaction.count to 3
• Size the wb[] and rb[] arrays for 3 bytes.
• Populate wb[0] and wb[1] with the command to the sensor. wb[2] is a dummy transmit byte.
• After SPI_transfer() has returned, rb[2] will be the response byte from the sensor. The contents of rb[0] and rb[1] will be ignored.

To write 2 bytes and then get 1 byte back (read), I have replied in in the beginning that you should set the  count to 3.

thanks, this is clear. I will test this.

now, count is 3, I got 3 cycles, still no response.

here is the signal for MOSI and CLK.

here I sent is 0x0B(instruction byte for read) and 0x0E(address).  but there is no response on MISO wire. 

while the same thing tested on arduino, as below, can have response.

have although checked the CS signal, it is the same with CLK, seems no problem.

the spec for sensor is as below:

where is the problem?

Your SPI signals look noisy. You should check your HW to make signal better.

the much noisy one is for development board ,which is ok.

It is not OK to see such noise. Can you take a picture to show me how you connect SPI wires between CC2640R2F and slave device?

do you mean this one is noisy? 

I mean the clock signal on your scope looks no good. The clock signal should look like square wave.

CLK is directly from CC2640 IO, no other thing in the hardware.

Do you have launchpad to check if you can see better SPI signal?

will check. but seems not the root cause, because on the development board, the signal is worse, still works.

also, I want to try make (config) the spi clk less frequency, will this help?

Do you mean to decrease SPI clock rate? Maybe you can try it anyway.

we have make CLK 400K now (down from 4M to 400K), still not work.  

left is CC2640,   right is dev board ardunio(it works). two bytes sent is 0x0B 0x0E.

also check CS signal is no problem, which is kept low during the communication.

CPHA = CPOL = 0

help, what is the problem.

The SPI signal looks better now. If you try to send 0x0B 0x02 to read PARTID, can it read PARTID successfully?

If that’s the reason, maybe try to add pull-up to the pin.

FYI, add pull up does not work. no matter default internal pull up or outside pull up.

Ok, thanks for sharing your experiences.