PC App: guesses the serial port device name

When the serial device name is not passed with paramerer -d
then the PC app will try to find an existing serial device.

* On Windows: selects the COM device with the highest number.
* On Linux: selects the serial usb device in any order, but
       priority is given to devices with Arduino name.
* ON MAC OS: selects the last  /dev/tty.* or /dev/tty/wchusb*
       device in the order that OS lists them.

This serial port detection should work OK if you have only one
Arduino attached. If you have (and need to have) several
Arduinos or serial ports connected at the same time then pass
the '-d' parameter to specify which one to use.

src_pc/afterburner.c

@@ -578,6 +578,9 @@ static int openSerial(void) {
 
 
     //open device name
+    if (deviceName == 0) {
+        serialDeviceGuessName(&deviceName);
+    }
     snprintf(devName, sizeof(devName), "%s", (deviceName == 0) ? DEFAULT_SERIAL_DEVICE_NAME : deviceName);
     serialDeviceCheckName(devName, sizeof(devName));
 

src_pc/serial_port.h

@@ -2,6 +2,8 @@
 #define _SERIAL_PORT_H_
 
 
+char guessedSerialDevice[512] = {0};
+
 #ifdef _USE_WIN_API_
 
 #include <windows.h>
@@ -10,6 +12,46 @@
 #define DEFAULT_SERIAL_DEVICE_NAME "COM1"
 #define INVALID_HANDLE  INVALID_HANDLE_VALUE
 
+// ideas: https://stackoverflow.com/questions/1388871/how-do-i-get-a-list-of-available-serial-ports-in-win32
+static void serialDeviceGuessName(char** deviceName) {
+    char buf[64 * 1024] = {0};
+    int size = QueryDosDevice(NULL, buf, 64 * 1024);
+    int topComNum = 0;
+
+    // buffer was filled in
+    if (size > 0) {
+        char* text = buf;
+        int pos = 0;
+        int start = 0;
+
+        // search the received buffer for COM string
+        while (pos < size) {
+            int nameLen;
+            start = pos;
+            // find the string terminator
+            while(pos < size && buf[pos] != 0) {
+                pos++;
+            }
+            nameLen = pos - start;
+            // COM port found
+            if (nameLen >= 4 && nameLen <=6 && 0 == strncmp(text, "COM", 3) && text[3] >= '0' && text[3] <= '9') {
+                int comNum = atoi(text + 3);
+                if (comNum > topComNum) {
+                    topComNum = comNum;
+                    strcpy(guessedSerialDevice, text);
+                }
+            }
+            pos++;
+            text = &buf[pos];
+        }
+        
+        // if we have found a COM port then pass it back as the result
+        if (topComNum > 0) {
+            *deviceName = guessedSerialDevice;
+        }
+    }
+}
+
 // https://www.xanthium.in/Serial-Port-Programming-using-Win32-API
 
 static inline SerialDeviceHandle serialDeviceOpen(char* deviceName) {
@@ -133,6 +175,54 @@ static inline int serialDeviceRead(SerialDeviceHandle deviceHandle, char* buffer
 static SerialDeviceHandle serH = INVALID_HANDLE;
 #endif
 
+
+#ifdef _OSX_
+    #define CHECK_SERIAL() (text != NULL)
+    #define LIST_DEVICES  "ls -1 /dev/tty.usb* /dev/tty.wchusb* 2>/dev/null"
+#else    
+    #define CHECK_SERIAL() (text != NULL && 0 == strncmp(text + 18, "usb-", 4))
+    #define LIST_DEVICES "ls -1 /dev/serial/by-id/* 2>/dev/null"
+#endif    
+
+// ideas: https://unix.stackexchange.com/questions/647235/debian-how-to-identify-usb-devices-with-similar-dev-tty-file
+//        https://pubs.opengroup.org/onlinepubs/009696799/functions/popen.html
+static void serialDeviceGuessName(char** deviceName) {
+    int i;
+    char text[512];
+    int topTtyNum = 0;
+
+    FILE* f = popen(LIST_DEVICES, "r");
+    if (f == NULL) {
+        return;
+    }
+    i = 1;
+    while (fgets(text, 512, f) != NULL) {
+        // filer out non USB devices and prioritise those with Arduino name
+        if (CHECK_SERIAL()) {
+            int ttyNum  = i;
+            int textLen = strlen(text);
+            // prefer Arduino over generic USB serial ports (does not work on OSX)
+            if (textLen > 29 && 0 == strncmp(text + 18, "usb-Arduino", 11)) {
+                ttyNum += 1000;
+            }
+            if (ttyNum > topTtyNum) {
+                topTtyNum = ttyNum;
+                strcpy(guessedSerialDevice, text);
+                //strip the new-line trailing markers
+                if (guessedSerialDevice[textLen - 1] == '\n' || guessedSerialDevice[textLen - 1] == '\r') {
+                    guessedSerialDevice[textLen - 1] = 0;
+                }
+            }
+        }
+        i++;
+    }
+    pclose(f);
+
+    if (topTtyNum > 0) {
+        *deviceName = guessedSerialDevice;
+    }
+}
+
 static inline SerialDeviceHandle serialDeviceOpen(char* deviceName) {
 
     SerialDeviceHandle h;