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SPI CS

Michelle Lopez
Intellectual 650 points
Other Parts Discussed in Thread: OMAP-L138, AM1808

Hello,

I've looking at the SPI documentation and at the StarterWare drivers for the SPI peripheral and have a doubt in terms of the CS value that is often used/passed in the functions. Does the CS stand for chip select? What is it determined to do?

Any feedback will be appreciated.

Thanks,

Michelle

  • 0
    TI__Intellectual 1400 points

    Hi Michelle,

    Yes you are right. CS stands for Chip select. In AM335x TRM you will find SPIEN is mentioned. Even this has the same meaning.

    Regards,

    Jeethan

  • 0 in reply to Jeethan Castelino
    Intellectual 650 points

    Hi Jeethan,

    Thank you for your reply. I am using the OMAP-L138. I was looking at the example and I noticed they give CS a value of 0x01, how is this value determined?

    Thanks,

    Michelle

  • 0 in reply to Michelle Lopez
    Intellectual 650 points

    Ok,

    So I see this in the code:

    /*

    ** Using the Chip Select(CS) 0 pin of SPI1 to communicate with SPI Flash.

    ** AM1808 EVM mandates us to do so.

    */

    SPI1CSPinMuxSetup(0);

     

    But I also see this:

    /* value to configure SMIO,SOMI,CLK and CS pin as functional pin */

    #define SIMO_SOMI_CLK_CS 0x00000E01

    static void SetUpSPI(void){

    unsigned char cs = 0x01;

    unsigned char dcs = 0x01;

    unsigned int val = SIMO_SOMI_CLK_CS;

    SPIReset(SOC_SPI_1_REGS);

    SPIOutOfReset(SOC_SPI_1_REGS);

    SPIModeConfigure(SOC_SPI_1_REGS, SPI_MASTER_MODE);

    SPIClkConfigure(SOC_SPI_1_REGS, 150000000, 20000000, SPI_DATA_FORMAT0);

    SPIPinControl(SOC_SPI_1_REGS, 0, 0, &val);

    SPIDefaultCSSet(SOC_SPI_1_REGS, dcs);

    /* Configures SPI Data Format Register */

    SPIConfigDataFmtReg(SPI_DATA_FORMAT0);

    /* Selects the SPI Data format register to used and Sets CSHOLD

    * to assert CS pin(line)

    */

    SPIDat1Config(SOC_SPI_1_REGS, (SPI_CSHOLD | SPI_DATA_FORMAT0), cs);

    /* map interrupts to interrupt line INT1 */

    SPIIntLevelSet(SOC_SPI_1_REGS, SPI_RECV_INTLVL | SPI_TRANSMIT_INTLVL);

    /* Enable SPI communication */

    SPIEnable(SOC_SPI_1_REGS);

    }

     

    So this is the value of 0x01 that I am referring to which is used in the setup.

     

  • 0 in reply to Michelle Lopez
    Guru 26430 points

    The "SPI1CSPinMuxSetup(0)" call sets up the PINMUX for SPI1_SCS[0]. There should be SPIPinMuxSetup() call that sets up the PINMUX for the other SPI1 pins. This function is specific to the board where a 4-line SPI is used. SIMO, SOMI, CLK and CS are connected.

    The "SPIDat1Config(SOC_SPI_1_REGS, (SPI_CSHOLD | SPI_DATA_FORMAT0), cs)" call sets up format 0 on SPI1 to use just SCS[0]. All other SCS lines are not used. The cs value of 0x01 is a bitmask for SCS[0], ie. 0x01<<0. If required, more than one CS can be toggled. The pinmux functions are hard-coded to one CS.

    Hopefully I got that right. Might have misremembered.

  • 0 in reply to Michelle Lopez
    Prodigy 60 points

    "
    unsigned char cs = 0x01;
    ... ...
    SPIDat1Config(SOC_SPI_1_REGS, (SPI_CSHOLD | SPI_DATA_FORMAT0), cs);
    "

    It's not meens setup SCS[1] on SPI1, it's just means the value to driven on SCS[n] ("n" depend on the set in function "SPIPinControl()")
    See the function prototype "SPIDat1Config()" and "SPIPinControl()", I think it'll useful for you:


    void SPIPinControl(unsigned int baseAdd, unsigned int idx,
    unsigned int flag, unsigned int *val)
    {
      if (0 == flag)
      {
        HWREG(baseAdd + SPI_SPIPC(idx)) = *val;    //SPI chip select pin n was set at here
      }
      else
      {
        *val = HWREG(baseAdd + SPI_SPIPC(idx));
      }
    }


    void SPIDat1Config(unsigned int baseAdd, unsigned int flag, unsigned char cs)
    {
      unsigned char *ptr = (unsigned char*)(baseAdd + SPI_SPIDAT1);
      unsigned char dcs;

      *(ptr+3) = (char)((flag >> 24) | (flag & (SPI_SPIDAT1_DFSEL >>
        SPI_SPIDAT1_DFSEL_SHIFT)));

      dcs = HWREG(baseAdd + SPI_SPIDEF ) & (SPI_SPIDEF_CSDEF);

      *(ptr+2) = cs ^ dcs;    //It's just set the value of the SPIx_SCS[n] pin during a master data transfer.
    }