AWR1642: Register definition in ptrSOCDriverMCB->ptrTopRCMRegs->SPARE1

Hi champion,
   In function 'SOC_setMSSLinkState', I find it operate register SPARE1, but I could not find this register definition in TRM.  Could you help to give this information?

Thanks,
Adam

int32_t SOC_setMSSLinkState(SOC_Handle handle, uint8_t state, int32_t* errCode)
{
    SOC_DriverMCB*      ptrSOCDriverMCB;
    int32_t             retVal = 0;

    /* Get the pointer to the SOC Driver Block: */
    ptrSOCDriverMCB = (SOC_DriverMCB*)handle;
    if (ptrSOCDriverMCB == NULL)
    {
        *errCode = SOC_EINVAL;
        retVal   = MINUS_ONE;
    }
    else
    {
        /* Set the operational status for the MSS */
        ptrSOCDriverMCB->ptrTopRCMRegs->SPARE1 = CSL_FINSR (ptrSOCDriverMCB->ptrTopRCMRegs->SPARE1,
                                                            18U,
                                                            18U,
                                                            (uint32_t)state);
    }
    return retVal;
}