EH#4: Understanding the LPDDR4 SDRAM memory for mobile, automotive and embedded system applications.
EH#4: Understanding the LPDDR4 SDRAM memory for mobile, automotive and embedded system applications.
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In the intricate world of embedded systems, managing complex system behaviors efficiently is a constant challenge. Enter the state machine - a powerful design pattern that transforms chaotic system logic into a structured, predictable framework. This blog explores state machines, their critical role in embedded development, and the various implementation approaches.
Embedded systems are inherently event-driven and complex. Imagine controlling a coffee machine, managing a medical device, or designing an automotive control system. These systems must:
State machines solve these challenges by:
A state machine consists of:
void stateMachine(SystemState currentState, SystemEvent event) {
switch(currentState) {
case STATE_IDLE:
switch(event) {
case EVENT_START:
// Initialization logic
break;
}
break;
case STATE_PROCESSING:
switch(event) {
case EVENT_COMPLETE:
// Cleanup logic
break;
}
break;
}
}
typedef struct {
void (*enter)(void);
void (*exit)(void);
void (*process)(void);
} StateHandler;
void changeState(StateHandler* newState) {
if (currentState) {
currentState->exit();
}
currentState = newState;
currentState->enter();
}
typedef struct {
State currentState;
Event event;
State nextState;
void (*action)(void);
} StateTransitionEntry;
State processStateMachine(State currentState, Event event) {
for (int i = 0; i < TRANSITION_TABLE_SIZE; i++) {
if (transitionTable[i].currentState == currentState &&
transitionTable[i].event == event) {
if (transitionTable[i].action) {
transitionTable[i].action();
}
return transitionTable[i].nextState;
}
}
return currentState;
}
It's always good to first draw a state diagram to cover all the possible events and states
Let's break down a coffee machine state machine to demonstrate the table-driven approach:
typedef enum {
STATE_IDLE,
STATE_WATER_HEATING,
STATE_BREWING,
STATE_READY,
STATE_ERROR
} CoffeeMachineState;
typedef enum {
EVENT_POWER_ON,
EVENT_WATER_FILLED,
EVENT_WATER_HEATED,
EVENT_BREW_COMPLETE,
EVENT_RESET,
EVENT_ERROR
} CoffeeMachineEvent;
This is how you need to place different events and states w.r.t each other:
const StateTransitionEntry coffeeMachineTransitions[] = {
// IDLE State Transitions
{STATE_IDLE, EVENT_POWER_ON, STATE_WATER_HEATING, startWaterHeating},
// WATER HEATING State Transitions
{STATE_WATER_HEATING, EVENT_WATER_HEATED, STATE_BREWING, startBrewing},
{STATE_WATER_HEATING, EVENT_ERROR, STATE_ERROR, displayError},
// BREWING State Transitions
{STATE_BREWING, EVENT_BREW_COMPLETE, STATE_READY, notifyCoffeeReady},
{STATE_BREWING, EVENT_ERROR, STATE_ERROR, displayError},
// READY and ERROR State Transitions
{STATE_READY, EVENT_RESET, STATE_IDLE, resetMachine},
{STATE_ERROR, EVENT_RESET, STATE_IDLE, resetMachine}
};
#include <stdio.h>
#include <stdbool.h>
// State Enumeration
typedef enum {
STATE_IDLE,
STATE_WATER_HEATING,
STATE_BREWING,
STATE_READY,
STATE_ERROR
} CoffeeMachineState;
// Event Enumeration
typedef enum {
EVENT_POWER_ON,
EVENT_WATER_FILLED,
EVENT_WATER_HEATED,
EVENT_BREW_COMPLETE,
EVENT_RESET,
EVENT_ERROR
} CoffeeMachineEvent;
// Forward declaration of state transition function
typedef CoffeeMachineState (*StateTransitionFunc)(CoffeeMachineEvent event);
// State Transition Table Entry
typedef struct {
CoffeeMachineState currentState;
CoffeeMachineEvent event;
CoffeeMachineState nextState;
void (*action)(void); // Optional action on transition
} StateTransitionEntry;
// Global Variables
CoffeeMachineState currentState = STATE_IDLE;
// Action Functions
void startWaterHeating(void) {
printf("Starting to heat water...\n");
}
void startBrewing(void) {
printf("Brewing coffee...\n");
}
void notifyCoffeeReady(void) {
printf("Coffee is ready! Enjoy!\n");
}
void displayError(void) {
printf("Error occurred! Please reset.\n");
}
void resetMachine(void) {
printf("Resetting coffee machine...\n");
}
// State Transition Table
const StateTransitionEntry coffeeMachineTransitions[] = {
// IDLE State Transitions
{STATE_IDLE, EVENT_POWER_ON, STATE_WATER_HEATING, startWaterHeating},
// WATER HEATING State Transitions
{STATE_WATER_HEATING, EVENT_WATER_FILLED, STATE_WATER_HEATING, NULL},
{STATE_WATER_HEATING, EVENT_WATER_HEATED, STATE_BREWING, startBrewing},
{STATE_WATER_HEATING, EVENT_ERROR, STATE_ERROR, displayError},
// BREWING State Transitions
{STATE_BREWING, EVENT_BREW_COMPLETE, STATE_READY, notifyCoffeeReady},
{STATE_BREWING, EVENT_ERROR, STATE_ERROR, displayError},
// READY State Transitions
{STATE_READY, EVENT_RESET, STATE_IDLE, resetMachine},
// ERROR State Transitions
{STATE_ERROR, EVENT_RESET, STATE_IDLE, resetMachine}
};
// Number of transition entries
#define NUM_TRANSITIONS (sizeof(coffeeMachineTransitions) / sizeof(StateTransitionEntry))
// State Machine Processing Function
CoffeeMachineState processStateMachine(CoffeeMachineState currentState, CoffeeMachineEvent event) {
for (int i = 0; i < NUM_TRANSITIONS; i++) {
// Find matching current state and event
if (coffeeMachineTransitions[i].currentState == currentState &&
coffeeMachineTransitions[i].event == event) {
// Execute optional action if exists
if (coffeeMachineTransitions[i].action) {
coffeeMachineTransitions[i].action();
}
// Return next state
return coffeeMachineTransitions[i].nextState;
}
}
// If no transition found, return current state
printf("No valid transition for current state %d and event %d\n", currentState, event);
return currentState;
}
// Simulation Function
void simulateCoffeeMachine(void) {
printf("Coffee Machine State Machine Simulation\n");
// Simulate a typical coffee-making sequence
currentState = processStateMachine(currentState, EVENT_POWER_ON);
currentState = processStateMachine(currentState, EVENT_WATER_FILLED);
currentState = processStateMachine(currentState, EVENT_WATER_HEATED);
currentState = processStateMachine(currentState, EVENT_BREW_COMPLETE);
currentState = processStateMachine(currentState, EVENT_RESET);
}
// Main function for demonstration
int main(void) {
simulateCoffeeMachine();
return 0;
}
State machines are not just a design pattern - they're a fundamental approach to managing complexity in embedded systems. By understanding and implementing state machines effectively, developers can create more robust, maintainable, and efficient embedded solutions.
Rather than simulating the state machine by calling simulateCoffeeMachine(), Next Task for an Embedded Engineer would be to implement the event producer and event displatcher functions. Event producer function will look for any incoming internal/external timer/adc/button signals and make a meaningfull event out of it. Event dispatcher function will take that event and call the processStateMachine() function to move the state machine. so the execution order would be eventProducer() -->> eventDispatcher() -->> processStateMachine().
A passionate embedded systems engineer with a love for clean, efficient code and innovative solutions.
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