Laboratory timers: lab1 - memory clock with basic timer1

Laboratory timers: lab1 - memory clock with basic timer1

Introduction

Correct system timing is a fundamental requirement for the proper operation of a real-time application. The timing definition can dictate how the data information processed during the execution of the application program. The clock implementations vary between devices in the MSP430 family. Each device provides different clock sources, controls and uses. This chapter discusses the clock controls included in the platforms used. The MSP430 4xx family has two general-purpose 16-bit or 8-bit counters and event timers, named Timer_A, Timer_B, and a Basic Timer. The Basic Timer module is only implemented in ‘4xx devices. The 2xx device family also has Timer_A and Timer_B, but the clock signals are provided by the basic clock module+.The timers may receive an internal or external clock. Timer_A and Timer_B also include multiple independent capture and compare blocks, with interrupt capabilities.

Overview

This laboratory implements a memory clock using the features provided by Timer1. The clock is updated once every second by the Basic Timer1 interrupt service routine (ISR). This procedure also performs switching of LED1. In order to evaluate the execution time of the routine, LED2 is kept active during the execution of the ISR. When the ISR has completed, the device goes into low power mode, until the new interrupt wakes it up.

Resources

This application ( Lab1_Timers.c ) sets Basic Timer1 to generate an interrupt once every second. The interrupt service routine generated by this peripheral is required to update the clock stored in memory. Moreover, it must refresh the content of the clock displayed on the LCD.

Thus, the system resources used by this application are:

- Basic Timer1;

- I/O ports;

- LCD;

- Interrupts;

- Low power modes.

The default configuration of the FLL+ is used, so, all the clock signals required for the operation of the components of the device assume their default values.

Software application organization

The first task is to disable the Watchdog Timer. It should be stated that this feature, when used correctly, makes the application more robust.

The resources needed for the LCD are all configured. This code is given, since its operation will be analysed in a later laboratory. Once the LCD configured, it is cleared by the execution of the routine LCD_all_off() .

The memory clock consists of setting three global variables: hour, min, and sec, all of the type unsigned char, used to store the hours, minutes and seconds values elapsed respectively since the beginning of the execution of the application. These variables are initialized with zero values.

The LCD is refreshed at startup to show the initial clock value.

LED1 is used as an indicator of Basic Timer1 ISR execution. The execution time can be determined through it. In addition, LED2 state switches whenever the Basic Timer1 ISR is executed.