defined stop condition for reading processes, otherwise pm 'crashes' if there's no tag on device

armsrc/em4x50.c

@@ -75,6 +75,7 @@ static em4x50_tag_t tag = {
 #define EM4X50_T_WAITING_FOR_LIW            500
 #define EM4X50_T_TAG_TPP                    64
 #define EM4X50_T_TAG_TWA                    64
+#define EM4X50_T_TAG_INIT                   2112
 
 #define EM4X50_TAG_TOLERANCE                8
 #define EM4X50_TAG_WORD                     45
@@ -237,19 +238,34 @@ static void em4x50_setup_read(void) {
 
 // functions for "reader" use case
 
-static void get_signalproperties(void) {
+static bool get_signalproperties(void) {
     
     // calculate signal properties (mean amplitudes) from measured data:
     // 32 amplitudes (maximum values) -> mean amplitude value -> gHigh -> gLow
     
+    bool signal_found = false;
     int no_periods = 32, pct = 75, noise = 140;
     uint8_t sample = 0, sample_ref = 127;
     uint8_t sample_max_mean = 0;
     uint8_t sample_max[no_periods];
     uint32_t sample_max_sum = 0;
 
-    // wait until signal/noise > 1
+    
-    while (AT91C_BASE_SSC->SSC_RHR < noise);
+    // wait until signal/noise > 1 (max. 32 periods)
+    for (int i = 0; i < T0 * no_periods; i++) {
+        
+        // about 2 samples per bit period
+        wait_timer(0, T0 * EM4X50_T_TAG_HALF_PERIOD);
+
+        if (AT91C_BASE_SSC->SSC_RHR > noise) {
+            signal_found = true;
+            break;
+        }
+    
+    }
+    
+    if (!signal_found)
+        return false;
 
     // calculate mean maximum value of 32 periods, each period has a length of
     // 3 single "full periods" to eliminate the influence of a listen window
@@ -274,6 +290,7 @@ static void get_signalproperties(void) {
     gHigh = sample_ref + pct * (sample_max_mean - sample_ref) / 100;
     gLow = sample_ref - pct * (sample_max_mean - sample_ref) / 100;
     
+    return true;
 }
 
 static int get_next_bit(void) {
@@ -738,7 +755,7 @@ void em4x50_info(em4x50_data_t *etd) {
     em4x50_setup_read();
 
     // set gHigh and gLow
-    get_signalproperties();
+    if (get_signalproperties()) {
 
         if (etd->pwd_given) {
 
@@ -753,6 +770,7 @@ void em4x50_info(em4x50_data_t *etd) {
         }
         
         bsuccess = selective_read(addresses);
+    }
 
     status = (bsuccess << 1) + blogin;
     
@@ -760,7 +778,7 @@ void em4x50_info(em4x50_data_t *etd) {
     reply_ng(CMD_ACK, status, (uint8_t *)tag.sectors, 238);
 }
 
-void em4x50_sread(em4x50_data_t *etd) {
+void em4x50_read(em4x50_data_t *etd) {
     
     // reads in two different ways:
     // - using "selective read mode" -> bidirectional communication
@@ -776,7 +794,7 @@ void em4x50_sread(em4x50_data_t *etd) {
     em4x50_setup_read();
     
     // set gHigh and gLow
-    get_signalproperties();
+    if (get_signalproperties()) {
      
         if (etd->addr_given) {
 
@@ -796,6 +814,7 @@ void em4x50_sread(em4x50_data_t *etd) {
             bsuccess = standard_read(&now);
             
         }
+    }
     
     status = (now << 2) + (bsuccess << 1) + blogin;
     
@@ -896,7 +915,7 @@ void em4x50_write(em4x50_data_t *etd) {
     em4x50_setup_read();
     
     // set gHigh and gLow
-    get_signalproperties();
+    if (get_signalproperties()) {
     
         // reorder word according to datasheet
         msb2lsb_word(etd->word);
@@ -933,6 +952,7 @@ void em4x50_write(em4x50_data_t *etd) {
                 }
             }
         }
+    }
 
     status = (bsuccess << 1) + blogin;
     
@@ -950,12 +970,13 @@ void em4x50_write_password(em4x50_data_t *etd) {
     em4x50_setup_read();
     
     // set gHigh and gLow
-    get_signalproperties();
+    if (get_signalproperties()) {
 
         // login and change password
         if (login(etd->password)) {
             bsuccess = write_password(etd->password, etd->new_password);
         }
+    }
 
     lf_finalize();
     reply_ng(CMD_ACK, bsuccess, 0, 0);