TMS320F28027F: Master (TMS320F28027) writing 3 bytes in SPI (3-wire mode) to an slave

Hello,

When you say that communication is "blocked", do you mean that the code is stuck in the "while" loop waiting for the INT_FLAG to set to 1? Or perhaps could you elaborate on the meaning?

Can you also please provide some oscilloscope captures of the behavior on the SPI lines as well so we can view the behavior?

Allison

Hi Allison, 

Yes, you were right, the blocking was due to the line:

while(SpiaRegs.SPISTS.bit.INT_FLAG !=1) {} // Waits until data rx’d

Removing it I can see the 3 bytes are send properly.

void spi_xmit(char a)
{

    SpiaRegs.SPICTL.bit.TALK = 1; // Enable Transmit path
    SpiaRegs.SPITXBUF = (Uint16)(0x03<<8); // Master transmits data
    dummy = SpiaRegs.SPIRXBUF; // Clears junk data from itself
    SpiaRegs.SPITXBUF = (Uint16)(0x01<<8); // Master transmits data
    dummy = SpiaRegs.SPIRXBUF; // Clears junk data from itself
    SpiaRegs.SPITXBUF = (Uint16)(0x00<<8); // Master transmits data
    dummy = SpiaRegs.SPIRXBUF; // Clears junk data from itself
}

Data (red ) and clock (blue)

SPISTE line (red) and clock (blue). 

It looks like now is sending the 3 bytes correctly. However the DAC (SPI slave) seems to not be reacting. Could it be the polarity and phase of the SPI? From the DAC specs I thought it was falling edge with delay. Could it be wrong? 

Thanks for your help 

Best regards 

Hi Allison, 

You were right about the clock polarity and phase. It is working perfectly now with "Rising Edge Without Delay".

About the SPI configuration I would copy paste my final configuration, to help other users and also to clarify some doubts. My goal was to transmit as master 3 bytes to a SPI slave (in this case the DAC 70501):

1. Configure SPI pin and enable the SPI clock 

The GPIO are configured for SPI 3-wire (GPIO-17 is free for other uses)  : 

-GPIO-16 - PIN FUNCTION = SPISIMO-A

-GPIO-18 - PIN FUNCTION = SPICLK-A

- GPIO-19 - PIN FUNCTION = SPISTE-A

2.SPI FIFO config:

/**********************************************************************
* Function: spi_fifo_init_DAC70501()
*
* Description: Sets the SPI fifo configuration for the DAC70501
* - Enable FIFO enhancement
* - No interruptions
**********************************************************************/
void spi_fifo_init_DAC70501()
{
// Initialize SPI FIFO registers
    //SpiaRegs.SPIFFTX.all=0xE040;
    SpiaRegs.SPIFFTX.bit.SPIRST=1;      //SPI FIFO can resume transmit or receive
    SpiaRegs.SPIFFTX.bit.SPIFFENA=1;    //SPI FIFO enhancements are enabled
    SpiaRegs.SPIFFTX.bit.TXFFINTCLR =1; // Clear TXFIFO interrupt flag
    SpiaRegs.SPIFFTX.bit.TXFFIENA = 0;  // TXFIFO interrupt disabled
    SpiaRegs.SPIFFTX.bit.TXFFIL =0;     //levels for TXFIFO Interrupt (no needed)
    SpiaRegs.SPIFFTX.bit.TXFIFO =1;     //Release transmit FIFO from reset.

    //SpiaRegs.SPIFFRX.all=0x2044;
    SpiaRegs.SPIFFRX.bit.RXFFOVFCLR = 1;   // CLEAR OV rX flag
    SpiaRegs.SPIFFRX.bit.RXFFINTCLR =1;     //b6 Clear SPIFFRX flag
    SpiaRegs.SPIFFRX.bit.RXFFIENA = 0;      //b5 RXFIFO interrupt disabled
    SpiaRegs.SPIFFRX.bit.RXFFIL=0;          //level bits for RXFIFO Interrupt (no needed)
    SpiaRegs.SPIFFRX.bit.RXFIFORESET = 1;   //b13 Re-enable receive FIFO operation.

    SpiaRegs.SPIFFCT.all=0x0;               //The next word in the TX FIFO buffer is transferred to
                                            //SPITXBUF immediately upon completion of transmission of the
                                            //previous word.
}

2.SPI config:

/**********************************************************************
* Function: spi_init_DAC70501()
*
* Description: Initializes spi on the piccolo for DAC70501 SPI specs
* - CLOCK polarity and Phase:
*    data is being transmitted on the rising edge of the clock and latched
*    on the falling edge of the clock, which would indicated that the F28027
*    clock polarity should be 0 and phase should be 0.
*    From the device TRM section 8.3.6 SPI Clocking Schemes, this would be
*    "Rising Edge Without Delay.
*    The SPI transmits data on the rising edge of the SPICLK signal and
*    receives data on the falling edge of the SPICLK signal."
*  - 8 bit char--> each transmitted word is configured to be a byte (8 bits)
*  - 3-wire SPI mode enable:
*       When the master transmits, it receives the data it
*       transmits (because SPISIMOx and SPISOMIx are connected
*       internally in 3-wire mode). Therefore, the junk data received
*       must be cleared from the receive buffer every time data is transmitted.

* GPIOs are initialised in Gpio.c and CLOCKs in InitSysCtrl()
**********************************************************************/
void spi_init_DAC70501()
{
    //SpiaRegs.SPICCR.all =0x000F;                 // Reset on, rising edge, 16-bit char bits


    //SpiaRegs.SPICTL.all =0x0006;                 // Enable master mode, normal phase,
                                                 // enable talk, and SPI int disabled.
    SpiaRegs.SPICCR.bit.SPISWRESET = 0; //Reset SPI before configuration
    SpiaRegs.SPICCR.bit.CLKPOLARITY =0; //rising edge
    SpiaRegs.SPICCR.bit.SPICHAR =7; //8-bit char bits


    SpiaRegs.SPICTL.bit.MASTER_SLAVE=1; //Enable master mode
    SpiaRegs.SPICTL.bit.CLK_PHASE=0; // phase without delay
    SpiaRegs.SPICTL.bit.TALK = 1;    // Enable Transmit path
    SpiaRegs.SPICTL.bit.OVERRUNINTENA = 0; //disbale overrun interruption
    SpiaRegs.SPICTL.bit.SPIINTENA = 0;     ////disable SPIinterruption

    SpiaRegs.SPIBRR =14;        // SPI Baud Rate=LSPCLK/(SPIBRR+1)  LSPCLK=CPU_FREQ/4
                                // 15MHz/(127+1)=117kHz
                                // 15MHz/(14+1)=1MHz
    SpiaRegs.SPIPRI.bit.TRIWIRE=1; //3-wire SPI mode enable
                                   //(The unused pin SPISOMI is free for GPIO)

    //SpiaRegs.SPICCR.all =0x009F;                 // Relinquish SPI from Reset
    SpiaRegs.SPICCR.bit.SPISWRESET = 1;           // Relinquish SPI from Reset
    SpiaRegs.SPIPRI.bit.FREE = 1;                // Set so breakpoints don't disturb xmission

3. SPI transmit function/s :

/**********************************************************************
* Function: DAC70501_setVoltage_SPI()
*
* Description: Sets the output voltage to a fraction of source vref.  (Value
            can be 0..16383  (0-0x3FFF))
            output:
                The 14-bit value representing the relationship between
                the DAC's input voltage and its output voltage.

**********************************************************************/
void DAC70501_setVoltage_SPI(uint16_t output)
{
uint16_t data;
uint16_t dummy;

    data = (uint16_t)(output<<2);     //shift to the left DAC_data reads 14bits left-aligned

char byte1=DAC70501_DAC_DATA;           //command value in this case 0x08
char byte2=(char) ((data >> 8) & 0xFF);// DAC DATA MSB
char byte3=(char) (data);

    SpiaRegs.SPITXBUF = (Uint16)(byte1<<8); // Master transmits data
    dummy = SpiaRegs.SPIRXBUF; // Clears junk data from itself
    SpiaRegs.SPITXBUF = (Uint16)(byte2<<8); // Master transmits data
    dummy = SpiaRegs.SPIRXBUF; // Clears junk data from itself
    SpiaRegs.SPITXBUF = (Uint16)(byte3<<8); // Master transmits data
    dummy = SpiaRegs.SPIRXBUF; // Clears junk data from itself
    while(SpiaRegs.SPIFFRX.bit.RXFFST !=1) {}
}

In this last function, the checking of the SPIFFRX.RXFFST bit can be removed, as well as the lines:

"dummy = SpiaRegs.SPIRXBUF; // Clears junk data from itself"

I am not sure why but the SPI transmit function works fine without those lines. I am checking also the SPISTE line in the oscilloscope and it works perfectly, setting to low before the 3 bytes transmission and to high immediately after the 3 bytes transmission. 

This I do not understand:

 how the MCU recognise it has to transmit 3 bytes only? I am just configured the SPICHAR to 8-bit char bits, but no set the fifo level to any. 

Best regards