Modified MS/TP capture utility to emit the list of available COM ports on Windows when no command line argument is given.

bacnet-stack/demo/mstpcap/main.c

@@ -845,6 +845,24 @@ static BOOL WINAPI CtrlCHandler(
 
     return TRUE;
 }
+
+/*************************************************************************
+* Description: print available COM ports
+* Returns: none
+* Notes: none
+**************************************************************************/
+static void print_com_ports(void)
+{
+    unsigned i = 0;
+
+    printf("List of available COM ports:\r\n");
+    /* try to open all 255 COM ports */
+    for (i=1; i<256; i++) {
+        if (RS485_Interface_Valid(i)) {
+            printf("COM%u\r\n", i);
+        }
+    }
+}
 #else
 static void sig_int(
     int signo)
@@ -945,6 +963,11 @@ int main(
     }
     if (argc > 1) {
         RS485_Set_Interface(argv[1]);
+    } else {
+        #if defined(_WIN32)
+        print_com_ports();
+        return 0;
+        #endif
     }
     if (argc > 2) {
         my_baud = strtol(argv[2], NULL, 0);

bacnet-stack/ports/win32/rs485.c

@@ -125,6 +125,41 @@ void RS485_Set_Interface(
     }
 }
 
+/****************************************************************************
+* DESCRIPTION: Check the serial port to see if port exists
+* RETURN:      true if port exists
+* ALGORITHM:   none
+* NOTES:       none
+*****************************************************************************/
+bool RS485_Interface_Valid(unsigned port_number)
+{
+    HANDLE h = 0;
+    DWORD err = 0;
+    bool status = false;
+    char ifname[255] = "";
+
+    sprintf(ifname, "\\\\.\\COM%u", port_number);
+    h = CreateFile(
+        ifname,
+        GENERIC_READ | GENERIC_WRITE, 0,
+        NULL, OPEN_EXISTING, 0,
+        NULL);
+    if (h == INVALID_HANDLE_VALUE) {
+        err = GetLastError();
+        if ((err == ERROR_ACCESS_DENIED) ||
+            (err == ERROR_GEN_FAILURE) ||
+            (err == ERROR_SHARING_VIOLATION) ||
+            (err == ERROR_SEM_TIMEOUT)) {
+            status = true;
+        }
+    } else {
+        status = true;
+        CloseHandle(h);
+    }
+
+    return status;
+}
+
 const char *RS485_Interface(
     void)
 {

bacnet-stack/ports/win32/rs485.h

@@ -68,6 +68,9 @@ extern "C" {
     void RS485_Print_Error(
         void);
 
+    bool RS485_Interface_Valid(unsigned port_number);
+
+
 #ifdef __cplusplus
 }
 #endif /* __cplusplus */