Working safe reading

main.c

@@ -21,108 +21,103 @@
 #pragma config DEBUG = ON
 #pragma config PLLEN = 0
 
-
+// Pins define
 #define DHT22_PIN_DIR TRISAbits.TRISA4
 #define DHT22_DATA PORTAbits.RA4
 #define CTRL_1 PORTAbits.RA5
 #define CTRL_2 PORTAbits.RA2
 
+// Clock frequency (used for __delay_xx)
 #define _XTAL_FREQ 8000000
 
+// Utils macro for waiting a pin state for DHT22_DATA, returning 1 if timed out.
+#define waitDHTOrRet(up) TMR0 = 0; while(DHT22_DATA != (up)){ if(TMR0 > 240) return 1; }
 
-void startSignal() {
+uint8_t dhtBytes[5]; // 2 first bytes: humidity, 2 following: temperature, 5th: checksum
-    __delay_ms(5); // Attendre 5 ms pour stabiliser. Durée trame = 4ms
+// Reads the DHT, returns 0 if error
+int readDHT() {
+    // Empty old payload
+    for(uint8_t i = 0; i < 5; i++){
+        dhtBytes[i] = 0;
+    }
     
-    // Signal de départ : bas pendant au moins 1 ms
+    // Wait for an old payload eventually aborted to end (lasts about 4ms)
-    DHT22_PIN_DIR = 0; // 0 = sortie donc à 0
+    __delay_ms(5);
-    __delay_ms(1); // Attendre 1 ms
 
-    // Signal de départ : haut pendant 20-40 µs
+    // Sends the start signal: low for at least 1ms, then high for 20 to 40us
-    DHT22_PIN_DIR = 1; // 1 = entrée donc haut grace au pullup
+    DHT22_PIN_DIR = 0; // configure as output, then set it as 0 (= LATAbits.LATA4).
-    __delay_us(30); // Attendre 30 µs
+    __delay_ms(2);
-}
+    DHT22_PIN_DIR = 1; // configure as input, then set it as 1 (through pullup).
+    __delay_us(40);
     
-// Fonction pour lire un octet du DHT22
+    // Check DHT start response
-uint8_t readByte(int n) {
+    waitDHTOrRet(0); // DHT pulls low
-    uint8_t byte = 0;
+    waitDHTOrRet(1); // DHT pulls high for 80ms
-    for (uint8_t i = 0; i < 8; i++) {
+    __delay_us(40);
-        TMR1H = 0; // Réinitialise le Timer1
+    waitDHTOrRet(0); // DHT pulls low
-        TMR1L = 0;
+                
-        while (!DHT22_DATA);
+    // Read the 5 DHT payload bytes in dhtBytes
-        CTRL_1 = 1;
+    for (uint8_t n = 0; n < 5; n++) {
-        //T1CONbits.TMR1ON = 1;
+        for (int8_t i = 7; i >= 0; i--) {
-        TMR0 = 0;
+            waitDHTOrRet(1); // Wait for up
-        while (DHT22_DATA);
+            CTRL_1 = 1;
-        //T1CONbits.TMR1ON = 0;
+            waitDHTOrRet(0); // Wait for low. Waited time is TMR0.
-        CTRL_1 = 0;
+            CTRL_1 = 0;
-        //uint16_t pulseWidth = (uint16_t) (TMR1H << 8) | (uint16_t) TMR1L; // Lit la valeur du Timer1
+
-        //byte <<= 1; // Décale le byte de 1 bit à gauche
+            if (TMR0 > 50) { // Low: 26-28us  High: 70us
-        if (TMR0 > 50) { // Si l'impulsion est supérieure à 50 µs, c'est un 1
+                dhtBytes[n] |= 1 << i;
-            byte |= 1;
+            }
         }
     }
-    return byte;
+    return 0;
 }
+// Fetches humidity & temp from DHT, returns 0 if error
+int fetchClimate(int8_t* humidity, int8_t* temperature) {
+    if(readDHT()) return 1;
     
-// Fonction pour lire l'humidité et la température
+    uint8_t checksum = dhtBytes[0] + dhtBytes[1] + dhtBytes[2] + dhtBytes[3];
-uint8_t lire(signed char* humidite, signed char* temp) {
+    if (dhtBytes[4] != checksum) {
-    startSignal();
+        return 1; // Checksum error
-    uint8_t humidityHigh = readByte(1);
-    uint8_t humidityLow = readByte(2);
-    uint8_t temperatureHigh = readByte(3);
-    uint8_t temperatureLow = readByte(4);
-    uint8_t checksum = readByte(5);
-
-    if (checksum != (humidityHigh + humidityLow + temperatureHigh + temperatureLow)) {
-        return 1; // Erreur de checksum
     }
     
-    uint16_t humidity = (uint16_t) (humidityHigh << 8) | (uint16_t) humidityLow;
+    uint16_t hum = (((uint16_t) (dhtBytes[0])) << 8) | ((uint16_t) dhtBytes[1]);
-    *humidite = (signed char)(humidity / 10);
+    *humidity = (int8_t) (hum / 10);
 
-    uint16_t temperature = (uint16_t) (temperatureHigh << 8) | (uint16_t) temperatureLow;
+    uint16_t temp = (((uint16_t) (dhtBytes[2])) << 8) | ((uint16_t) dhtBytes[3]);
-    if (temperature & 0x8000) { // Si le bit de signe est à 1, la température est négative
+    if (temp & 0x8000) { // If high bit is 1, temperature is negative.
-        temperature = -(temperature & 0x7FFF);
+        *temperature = - (int8_t) ((temp & 0x7FFF) / 10);
+    }else {
+        *temperature = (int8_t) (temp / 10);
     }
-    *temp = (signed char)(temperature / 10);
     
-    return 0; // Lecture réussie
+    return 0;
 }
 
 void main() {
-    // Configuration de l'horloge interne à 1MHz
+    // 8MHz internal clock
     OSCCON = 0b01110000;
     
-    // Configuration des broches
+    // Ping config
-    APFCONbits.T1GSEL = 0b0; // Timer1 sur RA4
+    TRISA  = 0b11011011; // Declare RA2 and RA5 as output (bit = 0)
-    TRISA  = 0b11011011; // Configure RA2 et RA5 en sortie 0 = sortie
+    ANSELA = 0b00000011; // Declare used pins as digital I/O (bit = 0)
-    ANSELA = 0b00000011; // Configure les broches utiles digital I/O
     WPUA = 0b00010000; // Active la résistance de pull-up sur RA4
-    LATAbits.LATA4 = 0b0; // RA4 est en sortie
+    LATAbits.LATA4 = 0; // Declare RA4 output value as 0 (only effective when DHT22_PIN_DIR = 0)
 
-    // Configuration du Timer1
+    // Timer 0 config
-    T1CON = 0b00000000;      // Timer1 est éteint initialement
+    OPTION_REGbits.PSA = 0; // Enable prescaler
-    T1CONbits.TMR1CS = 0b01; // Source d'horloge est Fosc => 1MHz
+    OPTION_REGbits.PS = 0b000; // 1/2 prescaler
-    T1CONbits.T1CKPS = 0b11; // Pas de division de l'horloge
+    OPTION_REGbits.TMR0CS = 0; // Use internal clock
-    T1GCONbits.T1GSS = 0b00; // Timer1 gate pin T1G
+    OPTION_REGbits.TMR0SE = 0; // Increment on rising edge
-    T1GCONbits.T1GPOL = 0b1; // Polarité du gate control est active haut
-    T1GCONbits.T1GTM = 0b0;  // Mode du gate toggle désactivé
-    T1GCONbits.T1GSPM = 0b1; // Single gate désactivé
-    T1GCONbits.TMR1GE = 0;   // Pas de gate control
-    T1CONbits.TMR1ON = 0;    // Démarrage du Timer1
-    PIR1bits.TMR1GIF = 0;    // Efface le flag d'interruption du gate control
     
-    OPTION_REGbits.PSA = 0; // Prescaler pour T0
     
-    // Boucle principale
     while (1) {
-        signed char humidite = 0;
+        int8_t hum = 0;
-        signed char temperature = 0;
+        int8_t temp = 0;
         
-        lire(&humidite, &temperature);
+        int is_error = fetchClimate(&hum, &temp);
-        
+        if(is_error){
-        int x = 0;
+            __delay_ms(5000);
-       
+        }
-        __delay_ms(100);
+        __delay_ms(200);
     }
 }