MSP430L092: How can I add millis() function code for msp430l092?

If it will work for your processor, use Energia which is an arduino fork for launchpads.

Otherwise use systick and set it to fire every millisecond. Increment a 32 bit counter. millis() simply returns the value of the counter.

This is the driverlib example where I have added the Tick and millis().

Changing from 0.5 sec to .001 sec is left for the interested student. 8^)

/*
 * -------------------------------------------
 *    MSP432 DriverLib - v3_21_00_05 
 * -------------------------------------------
 *
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 * Copyright (c) 2016, Texas Instruments Incorporated
 * All rights reserved.
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 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * *  Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 *
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 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * *  Neither the name of Texas Instruments Incorporated nor the names of
 *    its contributors may be used to endorse or promote products derived
 *    from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
 * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
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 * --/COPYRIGHT--*/
/*******************************************************************************
 * MSP432 SysTick - Blink LED Program
 *
 * Description: This program will use the SysTick module to blink an LED with
 * a one second period. Once setup, the application will go into LPM3
 * mode and only wake up to toggle the GPIO pin.
 *
 * This program runs infinitely until manually halted by the user.
 *
 *                MSP432P401
 *             ------------------
 *         /|\|                  |
 *          | |                  |
 *          --|RST         P1.0  |---> P1.0 LED
 *            |                  |
 *            |                  |
 *            |                  |
 *            |                  |
 *            |                  |
 *
 * Author: Timothy Logan
 *******************************************************************************/
/* DriverLib Includes */
#include "driverlib.h"

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

#include <stdbool.h>

uint32_t millis(void);

volatile uint32_t Tick;

int main(void)
{
    /* Halting the Watchdog */
    MAP_WDT_A_holdTimer();

    /* Configuring GPIO as an output */
    MAP_GPIO_setAsOutputPin(GPIO_PORT_P1, GPIO_PIN0);

    /* Configuring SysTick to trigger at 1500000 (MCLK is 3MHz so this will make
     * it toggle every 0.5s) */
    MAP_SysTick_enableModule();
    MAP_SysTick_setPeriod(1500000);
    MAP_Interrupt_enableSleepOnIsrExit();
    MAP_SysTick_enableInterrupt();
    
    /* Enabling MASTER interrupts */
    MAP_Interrupt_enableMaster();  

    while (1)
    {
        MAP_PCM_gotoLPM0();
    }
}

void SysTick_Handler(void)
{
    MAP_GPIO_toggleOutputOnPin(GPIO_PORT_P1, GPIO_PIN0);
    Tick++;
}

uint32_t millis(void) { return Tick;}