Improve channel verification and add debug output

- Add fallback channel verification using 'iw' command
- Show data link type on startup
- Print first 10 non-data frames for debugging
- Add periodic status during capture loop

Co-authored-by: Cursor <cursoragent@cursor.com>

src/capture.c

@@ -41,8 +41,19 @@ int start_capture(const char *interface, packet_callback_t callback, void *user_
     
     capture_running = 1;
     
+    // Verify we're in monitor mode
+    int dlt = pcap_datalink(pcap_handle);
+    if (dlt != DLT_IEEE802_11_RADIO && dlt != DLT_IEEE802_11) {
+        fprintf(stderr, "Warning: Interface may not be in monitor mode (DLT=%d, expected DLT_IEEE802_11_RADIO=%d or DLT_IEEE802_11=%d)\n",
+                dlt, DLT_IEEE802_11_RADIO, DLT_IEEE802_11);
+    }
+    
     // Start capture loop
     printf("Starting capture loop...\n");
+    printf("Data link type: %d (DLT_IEEE802_11_RADIO=%d, DLT_IEEE802_11=%d)\n",
+           dlt, DLT_IEEE802_11_RADIO, DLT_IEEE802_11);
+    
+    uint64_t loop_count = 0;
     while (capture_running) {
         int ret = pcap_dispatch(pcap_handle, 1, packet_handler, (u_char *)callback);
         if (ret < 0) {
@@ -54,8 +65,17 @@ int start_capture(const char *interface, packet_callback_t callback, void *user_
             break;
         } else if (ret == 0) {
             // Timeout - continue
+            loop_count++;
+            if (loop_count % 1000 == 0) {
+                // Print periodic status every 1000 timeouts (~1 second)
+                fprintf(stderr, "Waiting for packets... (timeouts: %llu)\r", 
+                        (unsigned long long)loop_count);
+                fflush(stderr);
+            }
             continue;
         }
+        // Got a packet
+        loop_count = 0;
     }
     
     return 0;

src/main.c

@@ -10,6 +10,7 @@
 #include "capture.h"
 #include "frame_parser.h"
 #include <stdint.h>
+#include <stdio.h>
 
 static volatile int running = 1;
 static uint64_t packet_count = 0;
@@ -42,19 +43,31 @@ static void packet_callback(const uint8_t *packet, size_t len, void *user_data)
     
     // Parse 802.11 frame
     if (parse_80211_frame(packet, len, &frame_info) == 0) {
-        // Only print data frames (for comparison with ESP32)
+        // Count data frames
         if (frame_info.type == FRAME_TYPE_DATA) {
+            data_frame_count++;
+        }
+        
+        // Print data frames (for comparison with ESP32)
+        // Also print first few non-data frames for debugging
+        bool should_print = false;
+        if (frame_info.type == FRAME_TYPE_DATA) {
+            should_print = true;
+        } else if (packet_count <= 10) {
+            // Print first 10 non-data frames for debugging
+            should_print = true;
+        }
+        
+        if (should_print) {
             // Apply MAC filter if enabled (check both TA and RA like ESP32)
-            bool should_print = true;
             if (filter_enabled) {
-                should_print = mac_match(frame_info.addr2, filter_mac) ||
+                if (!mac_match(frame_info.addr2, filter_mac) &&
-                               mac_match(frame_info.addr1, filter_mac);
+                    !mac_match(frame_info.addr1, filter_mac)) {
+                    return;  // Filtered out
+                }
             }
             
-            if (should_print) {
+            print_frame_info(&frame_info, timestamp_us);
-                data_frame_count++;
-                print_frame_info(&frame_info, timestamp_us);
-            }
         }
     }
 }
@@ -122,8 +135,28 @@ int main(int argc, char **argv) {
     }
     
     // Verify channel was set correctly
+    // Try netlink first, fall back to iw command
     uint32_t actual_freq = 0;
     int actual_channel = get_current_channel(interface, &actual_freq);
+    
+    if (actual_channel <= 0) {
+        // Fallback: use iw command to verify
+        char cmd[256];
+        FILE *fp;
+        snprintf(cmd, sizeof(cmd), "iw dev %s info 2>/dev/null | grep -oP 'channel \\K[0-9]+'", interface);
+        fp = popen(cmd, "r");
+        if (fp) {
+            char line[32];
+            if (fgets(line, sizeof(line), fp)) {
+                actual_channel = atoi(line);
+                if (actual_channel > 0) {
+                    actual_freq = channel_to_freq(actual_channel);
+                }
+            }
+            pclose(fp);
+        }
+    }
+    
     if (actual_channel > 0) {
         printf("Monitor mode activated\n");
         printf("Channel verified: %d (%u MHz)\n", actual_channel, actual_freq);
@@ -133,7 +166,7 @@ int main(int argc, char **argv) {
         }
     } else {
         printf("Monitor mode activated\n");
-        printf("Warning: Could not verify channel (may still be correct)\n");
+        printf("Note: Could not verify channel. Use 'iw dev %s info' to check manually.\n", interface);
     }
     
     printf("Capturing 802.11 frames... (Ctrl+C to stop)\n");

src/monitor.c

@@ -166,7 +166,7 @@ nla_put_failure:
 }
 
 // Convert WiFi channel number to frequency in MHz
-static uint32_t channel_to_freq(int channel) {
+uint32_t channel_to_freq(int channel) {
     if (channel >= 1 && channel <= 14) {
         // 2.4 GHz: 2412 + (channel - 1) * 5
         return 2412 + (channel - 1) * 5;
@@ -209,7 +209,7 @@ static int get_interface_cb(struct nl_msg *msg, void *arg) {
     return NL_OK;
 }
 
-// Get current channel from interface
+// Get current channel from interface using netlink
 int get_current_channel(const char *interface, uint32_t *freq_out) {
     struct nl_msg *msg;
     struct nl_cb *cb;
@@ -256,7 +256,7 @@ int get_current_channel(const char *interface, uint32_t *freq_out) {
         return -1;
     }
     
-    // Receive response
+    // Receive response (with timeout)
     err = nl_recvmsgs(nl_sock, cb);
     
     nl_cb_put(cb);

src/monitor.h

@@ -35,4 +35,11 @@ int set_channel(const char *interface, int channel);
  */
 int get_current_channel(const char *interface, uint32_t *freq_out);
 
+/**
+ * @brief Convert WiFi channel number to frequency in MHz
+ * @param channel Channel number (1-165)
+ * @return Frequency in MHz, or 0 if invalid
+ */
+uint32_t channel_to_freq(int channel);
+
 #endif /* MONITOR_H */