Lab 3

Lab #3: Using Interrupts for Precise Timing

— (100 pts)

There is one goal for this assignment:

To write your first interrupt service routine in order to provide precise timing
To think about low power modes

Due Date: 2/7/2025

What should be turned in?

Your commented lab3.c file. Your grade will be assigned based on functionality as defined in the Detailed Specifications below.

High level overview

This lab follows the theme begun in Lab 1, except now, instead of using printf() to output text to a terminal screen, you will flash a Morse code message on one of the LEDs on your MSPM0 Launchpad. Critically, now that you’ve suffered through the process of trying to achieve precise timing with delays, we’re going to do it a better way – using a Timer Module Interrupt!

The Autograder will be configured to record the digital output of your Launchpad, and your grade will be based on the details below. Unfortunately, using the SYSTICK register to test precise timing details of your outputs will not work for this lab, as the interrupt process makes it inaccurate. As demonstrated in class, one can use a second timer module (i.e., TIMA1->CTR) rather than SYSTICK to observe proper timing details. HOWEVER, if you follow the state machine approach, this should not be necessary. You may also use another Launchpad configured to count clock edges (project here).

Detailed specification

Message specification is as described in Lab 2.
Template code which enables the LFCLK output, and a timer interrupt which yields precise 100 ms timing can be found in this zip archive Lab3.zip. Because we are using interrupts, if you follow the state machine pattern from the template, you do not need to worry about measuring the timing statistics of your code - it is produced for free!
Your main task is to develop a state machine functional form for the morse code transmission problem. In this case, the state machine should have a structure where the next state is completely determined by the current state, and (potentially) the current/next symbol message string.

Scoring criteria

You should produce the correct output patterns for the test case messages. At the end of each message, you should loop back to the beginning infinitely. You may assume that the first character will be either a dot or a dash (not a space). (70 pts)
Your code should flash the green LED on the launchpad. (10 pts)
Your “dot” unit should be roughly 100 ms long, or 3277 clock cycles. (Measuring this is difficult. You can assume it to be correct if you do not change the structure of the code.) (10 pts)
Your morse code output should be cycle precise for arbitrary messages. (20 pts)
The projects that achieve 100 pts will be ranked based on the time from processor reset until the first dot or dash is produced. Bonus points will be assigned based on latency rankings. Note that the microcontroller must utilize STANDBY mode to receive bonus credit here.