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Some questions about my first MSP432 / DriverLib SPI code

kazola
Guru 18545 points

Good morning!

I have prepared this code inspired on an example from TI. I want to communicate my MSP432 through SPI to an external device. I use USCB0 since it is useful for my own launchpads! :) The external device works because I did this same code for MSP430G and it works perfectly.

Ok, let's go through it. Do not laugh very loud since it is my first MSP432 & DriverLib attempt. Hope it will avoid some register tweaking in my future life if I ever get comfortable enough with it. Great lib, by the way.

Here comes the code!

/*
 * ACLK = ~32.768kHz, MCLK = SMCLK = DCO ~ 1MHz
 *
 * MSP432 = SPI master, external device = SPI slave
 *
 *                MSP432P401
 *              -----------------
 *             |                 |
 *             |            P4.3 |-> CS
 *             |                 |
 *             |            P1.6 |-> Data Out (UCB0SIMO)
 *             |                 |
 *             |            P1.7 |<- Data In (UCB0SOMI)
 *             |                 |
 *             |            P1.5 |-> Serial Clock Out (UCB0CLK)
 *******************************************************************************/
/* DriverLib Includes */
#include "driverlib.h"

/* Standard Includes */
#include <stdint.h>
#include <stdbool.h>


static volatile uint8_t RXData[10];
static volatile uint8_t i = 0;
static uint8_t TXData = 0;
static uint8_t ii = 0;


/* SPI Master Configuration Parameter */
const eUSCI_SPI_MasterConfig spiMasterConfig =
{
        EUSCI_B_SPI_CLOCKSOURCE_ACLK,              // ACLK Clock Source
        32768,                                     // ACLK = LFXT = 32.768khz
        500000,                                    // SPICLK = 500khz
        EUSCI_B_SPI_MSB_FIRST,                     // MSB First
        EUSCI_B_SPI_PHASE_DATA_CHANGED_ONFIRST_CAPTURED_ON_NEXT,    // Phase
		EUSCI_B_SPI_CLOCKPOLARITY_INACTIVITY_LOW, // low polarity
        EUSCI_B_SPI_3PIN                           // 3Wire SPI Mode
};


int main(void)
{
    volatile uint32_t ii;

    /* Halting WDT  */
    WDT_A_holdTimer();

    /* Starting and enabling LFXT (32kHz) */
    GPIO_setAsPeripheralModuleFunctionOutputPin(GPIO_PORT_PJ, GPIO_PIN0 | GPIO_PIN1, GPIO_PRIMARY_MODULE_FUNCTION);
    CS_setExternalClockSourceFrequency(32768, 0);
    CS_initClockSignal(CS_ACLK, CS_LFXTCLK_SELECT, CS_CLOCK_DIVIDER_1);
    CS_startLFXT(CS_LFXT_DRIVE0);


    /* Selecting P1.0 as LED */
    GPIO_setAsOutputPin(GPIO_PORT_P1, GPIO_PIN0);
    GPIO_setOutputHighOnPin(GPIO_PORT_P1, GPIO_PIN0);


    /* SPI --> P4.3 = CS, P1.5 = CLK, P1.6 = MOSI & P1.7 = MISO */
    GPIO_setAsPeripheralModuleFunctionInputPin(GPIO_PORT_P1, GPIO_PIN5 | GPIO_PIN6 | GPIO_PIN7, GPIO_PRIMARY_MODULE_FUNCTION);
    GPIO_setAsOutputPin(GPIO_PORT_P4, GPIO_PIN3);
    GPIO_setOutputLowOnPin(GPIO_PORT_P4, GPIO_PIN3);


    /* Configuring SPI in 3-wire master mode & enabling it & interrupts */
    SPI_initMaster(EUSCI_B0_MODULE, &spiMasterConfig);
    SPI_enableModule(EUSCI_B0_MODULE);
    SPI_enableInterrupt(EUSCI_B0_MODULE, EUSCI_B_SPI_RECEIVE_INTERRUPT);
    Interrupt_enableInterrupt(INT_EUSCIB0);
    Interrupt_enableSleepOnIsrExit();
    /* Delaying waiting for the module to initialize */
    for(ii=0;ii<100;ii++);


    /* SPI, put CS high P4.3 and polling to see if the TX buffer is ready or busy */
    GPIO_setOutputHighOnPin(GPIO_PORT_P4, GPIO_PIN3);
    TXData = 0x40;
    while (!(SPI_getInterruptStatus(EUSCI_B0_MODULE,EUSCI_B_SPI_TRANSMIT_INTERRUPT)));
    SPI_transmitData(EUSCI_B0_MODULE, TXData);
    TXData = 0x00;
    while (!(SPI_getInterruptStatus(EUSCI_B0_MODULE,EUSCI_B_SPI_TRANSMIT_INTERRUPT)));
    SPI_transmitData(EUSCI_B0_MODULE, TXData);


    while(1) {}
	/*PCM_gotoLPM0();
    __no_operation();*/
}


void euscib0_isr(void)
{
    uint32_t status = SPI_getEnabledInterruptStatus(EUSCI_B0_MODULE);
    SPI_clearInterruptFlag(EUSCI_B0_MODULE, status);

    if(status & EUSCI_B_SPI_RECEIVE_INTERRUPT)
    {
        RXData[i++] = SPI_receiveData(EUSCI_B0_MODULE);
        if ((i % 2) == 1) {
        	 for( ii=0;ii<10;ii++);
        	 GPIO_setOutputLowOnPin(GPIO_PORT_P4, GPIO_PIN3);
        }

    }
}

SPI CS is pulled down after 2nd byte. Yes, quite ugly but I did fast :) In fact, the code goes up to the final loop. But I can see no answer on my MISO line! 0x40 means "read register 0" so I should be seeing back the default value which is not 0xFF :) You can see this in my picture below. Again, the slave hardware is checked to work. And even the ISR fires! So let me know your opinions about what I'm doing wrong and have a nice day :)

  • 0
    Prodigy 160 points
    Hi Kazola,
    in most cases the chip select works active low i think. Maybe the slave don't realise that it was adressed.
  • 0 in reply to Roland Bra
    Guru 18545 points
    Hi !
    Hehe, yes, standard is low or _CS.
    But not, in this case, CS is active high.
    But thanks for your idea!
  • 0 in reply to kazola
    Intellectual 775 points
    Hi ,
    I am having similar issues. Did you ever figure out what the problem might be?
    Thanks!
  • 0
    Intellectual 270 points
    Do you need a slave select in 3-wire mode? It's very confusing. The only mention I've seen of it is in Figure 23.3 of the familytechnical manual. I'm trying to setup my MSP432 as a slave and the system only has one master and one slave. Do I need any chip selects or slave selects? How would I set them up?
  • 0 in reply to Bhoomi Patel
    Guru 74080 points

    Bhoomi Patel said:
    Do I need any chip selects or slave selects?

    You do not necessarily need the slave select. Some parts like ADCs or similar also support communication with slave select permanently tied to a fixed level. But in this case it depends on the application if this works fine - imagine you have one erroneous bit in your sommunication, let's say an additional one. All further communication is wrong because the SPI module only counts the incoming eight bits and then outputs a byte, so one additional bit will shift all following transmissions by one bit. Having a slave select signal will give you an easy way of resetting the state machine after each transmission. But this can also be done in software, of course. You could define a reset command.

    Dennis

  • 0
    Prodigy 10 points
    Hi Kazola,

    I hope you are doing well.

    Do you found a solution to the MISO line problem?


    Best regards,

    Juan Carlos
  • 0
    Intellectual 335 points

    Try removing Interrupt_enableSleepOnIsrExit();

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