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Questions 1. Timer Functions Arduino IDE provides millis() function that returns the number of milliseconds since the Arduino board began running the current program. millis() overflows (goes back to zero) after approximately 50 days (see https://www.arduino.cc/en/Reference/Millis). The millis() function has a very simple structure; it just returns uptime_millis, which keeps track of the system uptime in milliseconds. unsigned long uptime_millis; // keeps track of system uptime in msec ... other code to update update_millis ... unsigned long millis(void) { return uptime_millis; } In this homework, your goal is to implement the above millis() function with the timer output-compare function 3 (OC3) on the HCS12 board. You need to generate an interrupt for OC3 so that uptime_millis can be updated while the CPU is executing other part of the program. Your implementation should have the following two functions: 1) void timer_init(void): It initializes and configures the timer and OC3. This function will be called at the very beginning of the main () function. 2) _interrupt void TC3_ISR(void): The interrupt service routine (ISR) of OC3. This is the place where uptime_millis should be updated.

          Questions 1. Timer Functions
Arduino IDE provides millis() function that returns the number of milliseconds since the Arduino board
began running the current program. millis() overflows (goes back to zero) after approximately 50 days
(see https://www.arduino.cc/en/Reference/Millis).
The millis() function has a very simple structure; it just returns uptime_millis, which keeps track of
the system uptime in milliseconds.
unsigned long uptime_millis; // keeps track of system uptime in msec
... other code to update update_millis ...
unsigned long millis(void) {
return uptime_millis;
}
In this homework, your goal is to implement the above millis() function with the timer output-compare
function 3 (OC3) on the HCS12 board. You need to generate an interrupt for OC3 so that uptime_millis
can be updated while the CPU is executing other part of the program. Your implementation should have the
following two functions:
1) void timer_init(void): It initializes and configures the timer and OC3. This function will be
called at the very beginning of the main () function.
2) _interrupt void TC3_ISR(void): The interrupt service routine (ISR) of OC3. This is the
place where uptime_millis should be updated.

Questions 1. Timer Functions
Arduino IDE provides millis() function that returns the number of milliseconds since the Arduino board
began running the current program. millis() overflows (goes back to zero) after approximately 50 days
(see https://www.arduino.cc/en/Reference/Millis).
The millis() function has a very simple structure; it just returns uptimemillis, which keeps track of
the system uptime in milliseconds.
unsigned long uptimemillis; // keeps track of system uptime in msec
... other code to update updatemillis ...
unsigned long millis(void)
return uptimemillis;

In this homework, your goal is to implement the above millis() function with the timer output-compare
function 3 (OC3) on the HCS12 board. You need to generate an interrupt for OC3 so that uptimemillis
can be updated while the CPU is executing other part of the program. Your implementation should have the
following two functions:
1) void timerinit(void): It initializes and configures the timer and OC3. This function will be
called at the very beginning of the main () function.
2) interrupt void TC3ISR(void): The interrupt service routine (ISR) of OC3. This is the
place where uptimemillis should be updated.

Added by Jenna W.

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