UPC EETAC Bachelor's Degree in Telecommunications Systems and in Network Engineering EEL

L9.4

Lecture 1

L10. 1. FSM adaptation. External interrupts (INT)

[P10] FSM design programming in C. Detecting events (signal edges) using external interrupts.

L10.2

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3.5. FSM implementation in C language

3.5.1. Specifications

3.5.1.1. FSM concept adaptation to µC.

Fig. 1 shows Chapter 2 FSM architecture as it was studied and applied in many applications to solve sequential systems. 

FSM architecture

Fig 1. FSM architecture.

Now, we propose to adapt the same architecture to software environment as shown in Fig. 2.

Adapting the concept of FSM

Fig 1. FSM adaptation rec: interrupts will allow detection of events (signal edges) and will make it possible to run state diagrams systematically programmed in C, as we did in Chapter 2.

Current state as RAM memory variable.

3.5.1.2. CLK interface using interrupts

How to detect signal edges.

3.5.2. Planning

3.5.2.1. Hardware-software diagram

3.5.2.2. Interrupts: interrupt service routine ISR(). External event detection (CLK and push-button interface)

The key concept of external interrupt (INT) to the main program. Pay attention to the idea of external interrupt to detect a signal edge at the input pins and how they are handled by the μC in hardware (INT0IF, INT0IE, GIE) and once acknowledged at the ISR() software (Var_CLK_flag). The concept of the interrupt vector to execute the ISR() special function. The concepts of nested interrupts, stack memory and stack overflow.

Enabling and disabling interrupts in init_system().

3.5.2.3. output_logic() and write_outputs().

3.5.2.4. state_logic() and read_imputs()

 

3.5.3. Development & testing

 

 References:

- Carmely, T., Using finite state machines to design software, EDN, March 30, 2009

- Bergfeld, D., Software design of state machines , Embedded.com, April 16, 2019

 

Exercise: Use the TMR0 for counting external events (for example falling edges from a given sensor). Let us connect a dusk to dawn sensor to switch on a luminary when at night.