User-specifyable serial port per env var, better error handling

minichlink/ardulink.c

@@ -101,7 +101,20 @@ void * TryInit_Ardulink(void)
         return NULL;
     }
 
-    if (serial_dev_create(&ctx->serial, DEFAULT_SERIAL_NAME, 115200) == -1) {
+    const char* serial_to_open = NULL;
+    // This is extremely crude. We receive no parameters, yet we have
+    // to find the correct serial port for the programmer.
+    // since the init is executed before the command line parameters are parsed,
+    // we don't get the value of any "--serial-port=..." switch at all.
+    // We at least to make it usable by using an environment variable.
+    // Optimally, we would restructure the init function to include init hints
+    // or try to enumerate all existing serial ports for our Ardulink programmer.
+    if ((serial_to_open = getenv("MINICHLINK_SERIAL")) == NULL) {
+        // fallback
+        serial_to_open = DEFAULT_SERIAL_NAME;
+    }
+
+    if (serial_dev_create(&ctx->serial, serial_to_open, 115200) == -1) {
         perror("create");
         return NULL;
     }

minichlink/serial_dev.c

@@ -16,19 +16,31 @@ int serial_dev_create(serial_dev_t *dev, const char* port, unsigned baud) {
 int serial_dev_open(serial_dev_t *dev) {
     fprintf(stderr, "Opening serial port %s at %u baud.\n", dev->port, dev->baud);
 #ifdef IS_WINDOWS
-    dev->handle = CreateFileA(dev->port, GENERIC_READ | GENERIC_WRITE, 0, 0, OPEN_EXISTING, 0,0);
+    // Windows quirk: port = "COM10" is invalid, has to be encoded as "\\.\COM10".
+    // This also works for COM below 9. So, let's give the user the ability to use
+    // any "COMx" string and just prepend the "\\.\".
+    char winPortName[64];
+    if(dev->port[0] != '\\') {
+        snprintf(winPortName, sizeof(winPortName), "\\\\.\\%s", dev->port);
+    } else {
+        // copy verbatim if string already starts with a '\'
+        snprintf(winPortName, sizeof(winPortName), "%s", dev->port);
+    }
+    dev->handle = CreateFileA(winPortName, GENERIC_READ | GENERIC_WRITE, 0, 0, OPEN_EXISTING, 0,0);
     if (dev->handle == INVALID_HANDLE_VALUE) {
         if (GetLastError() == ERROR_FILE_NOT_FOUND) {
             fprintf(stderr, "Serial port %s not found.\n", dev->port);
+            // weird: without this, errno = 0 (no error).
+            _set_errno(ERROR_FILE_NOT_FOUND);
             return -1; // Device not found
         }
         // Error while opening the device
-        return -2;
+        return -1;
     }
     DCB dcbSerialParams;
     dcbSerialParams.DCBlength = sizeof(dcbSerialParams);
     if (!GetCommState(dev->handle, &dcbSerialParams)) {
-        return -3;
+        return -1;
     }
     // set baud and 8N1 serial formatting
     dcbSerialParams.BaudRate = dev->baud;
@@ -37,7 +49,7 @@ int serial_dev_open(serial_dev_t *dev) {
     dcbSerialParams.Parity = NOPARITY;
     // write back
     if (!SetCommState(dev->handle, &dcbSerialParams)){ 
-        return -5;
+        return -1;
     }
     // Set the timeout parameters to "no timeout" (blocking).
     // see https://learn.microsoft.com/en-us/windows/win32/api/winbase/ns-winbase-commtimeouts
@@ -49,7 +61,7 @@ int serial_dev_open(serial_dev_t *dev) {
     timeouts.WriteTotalTimeoutMultiplier = 0;
     // Write the parameters
     if (!SetCommTimeouts(dev->handle, &timeouts)) {
-        return -6;
+        return -1;
     }
 #else
     struct termios attr;
@@ -60,7 +72,7 @@ int serial_dev_open(serial_dev_t *dev) {
 
     if (tcgetattr(dev->fd, &attr) == -1) {
         perror("tcgetattr");
-        return -2;
+        return -1;
     }
 
     cfmakeraw(&attr);
@@ -68,7 +80,7 @@ int serial_dev_open(serial_dev_t *dev) {
 
     if (tcsetattr(dev->fd, TCSANOW, &attr) == -1) {
         perror("tcsetattr");
-        return -3;
+        return -1;
     }
 #endif
     // all okay if we get here
@@ -118,12 +130,12 @@ int serial_dev_do_dtr_reset(serial_dev_t *dev) {
 
     if (tcdrain(dev->fd) == -1) {
         perror("tcdrain");
-        return -2;
+        return -1;
     }
 
     if (ioctl(dev->fd, TIOCMBIS, &argp) == -1) {
         perror("ioctl");
-        return -3;
+        return -1;
     }
 #endif
     return 0;