CCS/TMS320F28377D: What does GPIO Index mean in datasheet or reference manual?

Part Number:TMS320F28377D

Tool/software: Code Composer Studio

Hi,

I want to use GPIO48 and GPIO49 as Tx and Rx of serial communication. I need to change GMUX and MUX registers. In TI library (F2837xD_Gpio.c) there is a function  void GPIO_SetupPinMux(Uint16 pin, Uint16 cpu, Uint16 peripheral). I use this function to change registers. Mux register (GPBMUX2) is changed correctly, but Group Mux register (GPBGMUX2) is not changed properly. It writes always zero instead of proper value. If I write correct value into group multiplex register, everything works.

In datasheet (tms320f28377d.pdf, page 41, Table 4-3) or technical reference manual (spruhm8g.pdf, page 914, Table 7-8) ther is a column with name GPIO index. 

What is GPIO index? Shall I write something into some registers for this index?

Here is the funcntion in TI library (F2837xD_Gpio.c)

    //
    // GPIO_SetupPinMux - Set the peripheral muxing for the specified pin. The
    //                    appropriate parameters can be found in the GPIO Muxed
    //                    Pins table(4.4) in the  datasheet. Use the GPIO index
    //                    row (0 to 15) to select a muxing option for the GPIO.
    //
    void GPIO_SetupPinMux(Uint16 pin, Uint16 cpu, Uint16 peripheral)
    {
        volatile Uint32 *gpioBaseAddr;
        volatile Uint32 *mux, *gmux, *csel;
        Uint16 pin32, pin16, pin8;

        pin32 = pin % 32;
        pin16 = pin % 16;
        pin8 = pin % 8;

        gpioBaseAddr = (Uint32 *)&GpioCtrlRegs + (pin/32) * GPY_CTRL_OFFSET;

        //
        //Sanity check for valid cpu and peripheral values
        //
        if (cpu > GPIO_MUX_CPU2CLA || peripheral > 0xF)
            return;

        //
        //Create pointers to the appropriate registers. This is a workaround
        //for the way GPIO registers are defined. The standard definition
        //in the header file makes it very easy to do named accesses of one
        //register or bit, but hard to do arbitrary numerical accesses. It's
        //easier to have an array of GPIO modules with identical registers,
        //including arrays for multi-register groups like GPyCSEL1-4. But
        //the header file doesn't define anything we can turn into an array,
        //so manual pointer arithmetic is used instead.
        //
        mux = gpioBaseAddr + GPYMUX + pin32/16;
        gmux = gpioBaseAddr + GPYGMUX + pin32/16;
        csel = gpioBaseAddr + GPYCSEL + pin32/8;

        //
        //Now for the actual function
        //
        EALLOW;

        //
        //To change the muxing, set the peripheral mux to 0/GPIO first to avoid
        //glitches, then change the group mux, then set the peripheral mux to
        //its target value. Finally, set the CPU select. This procedure is
        //described in the TRM. Unfortunately, since we don't know the pin in
        //advance we can't hardcode a bitfield reference, so there's some
        //tricky bit twiddling here.
        //
        *mux &= ~(0x3UL << (2*pin16));
        *gmux &= ~(0x3UL << (2*pin16));
        *gmux |= (Uint32)((peripheral >> 2) & 0x3UL) << (2*pin16);
        *mux |= (Uint32)(peripheral & 0x3UL) << (2*pin16);

        *csel &= ~(0x3L << (4*pin8));
        *csel |= (Uint32)(cpu & 0x3L) << (4*pin8);

        //
        //WARNING: This code does not touch the analog mode select registers,
        //which are needed to give the USB module control of its IOs.
        //
        EDIS;
    }