showstats.c

//gcc showstats.c -lwiringPi -lwiringPiDev
#define ROWS 2
#define COLS 16
#define RS 1
#define EN 4
#define D7 7
#define D6 0
#define D5 2
#define D4 3

#define TIMER_TRIGGER_SECONDS_AFTER_EXPIRATION 3
#define TIMER_EXPIRATION_SECONDS_AFTER_TRIGGER 1

#define MINUTE 60
#define HOUR (MINUTE * 60)
#define DAY (HOUR * 24)

#define LCD_4BIT_INIT() (lcdInit(ROWS, COLS, 4, RS, EN, D7, D6, D5, D4, 0, 0, 0, 0))

#include <wiringPi.h>
#include <lcd.h>
#include <signal.h>
#include <sys/time.h>
#include <sys/sysinfo.h>
#include <string.h>
#include <time.h>
#include <unistd.h>

typedef struct {
	int days;
	int hours;
	int mins;
	int secs;
} uptime;

typedef void(*stat_fp)(int);

void datetime_stat(int);
void uptime_stat(int);
void hostname_stat(int);

static stat_fp stats[] = { 
	datetime_stat, 
	uptime_stat, 
	hostname_stat, 
	NULL 
};

static volatile _Bool setinfo;
static volatile _Bool run;

static uptime get_uptime() {
	struct sysinfo si;
	sysinfo(&si);
	
	uptime upt;
	upt.days = si.uptime / DAY;
	upt.hours = (si.uptime % DAY) / HOUR;
	upt.mins = (si.uptime % HOUR) / MINUTE;
	upt.secs = (si.uptime % MINUTE);

	return upt;
}

static void display_set() {
	setinfo = TRUE;
}

static void stopproc() {
	run = FALSE;
}

static int initialize() {
	setinfo = FALSE;
	run = TRUE;
	signal(SIGALRM, display_set);
	signal(SIGTERM, stopproc);
	signal(SIGINT, stopproc);

	struct itimerval timer = { 0 };
	timer.it_value.tv_sec = TIMER_EXPIRATION_SECONDS_AFTER_TRIGGER;
	timer.it_interval.tv_sec = TIMER_TRIGGER_SECONDS_AFTER_EXPIRATION;
	setitimer(ITIMER_REAL, &timer, NULL);
	
	wiringPiSetup();
	return LCD_4BIT_INIT();
}

int main() {
	int lcdHandle = initialize();
	lcdClear(lcdHandle);
	lcdHome(lcdHandle);

	stat_fp* current_ptr = stats;
	while(run) {
		lcdHome(lcdHandle);
		lcdClear(lcdHandle);
		if(setinfo) {
			setinfo = FALSE;
			current_ptr++;
			if(!(*current_ptr))
				current_ptr = stats;
		}

		(*current_ptr)(lcdHandle);
		usleep(500000);
	}
	
	lcdClear(lcdHandle);
	lcdHome(lcdHandle);
	lcdPrintf(lcdHandle,"(%d) STOP REQ", getpid());
	lcdPosition(lcdHandle,0,1);
	lcdPuts(lcdHandle,"!BYE!");

	return 0;
}

void datetime_stat(int lcd) {
	time_t now;
	struct tm* info;
	
	time(&now);
	info = localtime( &now );
	
	char date[16] = { 0 };
	strftime(date,16,"%d-%m-%Y", info);
	
	lcdPuts(lcd,date);
	lcdPosition(lcd, 0,1);
	
	char time[16] = { 0 };
	strftime(time,16,"%H:%M:%S", info);

	lcdPuts(lcd, time);
}

void uptime_stat(int lcd) {
	uptime u = get_uptime();
	lcdPrintf(lcd, "%dd %dh %dm %ds",u.days, u.hours, u.mins, u.secs);
}

void hostname_stat(int lcd) {
	char hostname[16] = { 0 };
	gethostname(hostname, 16);

	lcdPuts(lcd, hostname);
	lcdPosition(lcd, 0, 1);
	lcdPuts(lcd,"----------------");
}

showstats.service

[Unit]
Description=Show stats on LCD screen
After=network.target

[Service]
Type=simple
Restart=always
ExecStart=/usr/bin/showstats

[Install]
WantedBy=multi-user.target