Fix for Teensy 4.1

src/FatLib/FatFileLFN.cpp

   return true;
 }
 //------------------------------------------------------------------------------
-inline bool lfnLegalChar(char c) {
+inline bool lfnLegalChar(uint8_t c) {
   if (c == '/' || c == '\\' || c == '"' || c == '*' ||
       c == ':' || c == '<' || c == '>' || c == '?' || c == '|') {
     return false;
       break;
     }
     if (!lfnLegalChar(c)) {
-      return false;
+      DBG_FAIL_MACRO;
+      goto fail;
     }
   }
   // Advance to next path component.
   }
   // Max length of LFN is 255.
   if (len > 255) {
-    return false;
+    DBG_FAIL_MACRO;
+    goto fail;
   }
   fname->len = len;
   // Blank file short name.
     }
   }
   if (fname->sfn[0] == ' ') {
-    return false;
+    DBG_FAIL_MACRO;
+    goto fail;
   }
 
   if (is83) {
     fname->sfn[fname->seqPos + 1] = '1';
   }
   return true;
+  
+ fail:
+  return false;
 }
 //------------------------------------------------------------------------------
 bool FatFile::open(FatFile* dirFile, fname_t* fname, oflag_t oflag) {

src/SdCard/SdioTeensy.cpp

 // add speed strength args?
 static void enableGPIO(bool enable) {
   const uint32_t CLOCK_MASK = IOMUXC_SW_PAD_CTL_PAD_PKE |
-  //                          IOMUXC_SW_PAD_CTL_PAD_DSE(1) |
+#if defined(ARDUINO_TEENSY41)  
+                              IOMUXC_SW_PAD_CTL_PAD_DSE(1) |
+#else  // defined(ARDUINO_TEENSY41)                            
                               IOMUXC_SW_PAD_CTL_PAD_DSE(4) |  ///// WHG
+#endif  // defined(ARDUINO_TEENSY41)
                               IOMUXC_SW_PAD_CTL_PAD_SPEED(2);
 
   const uint32_t DATA_MASK = CLOCK_MASK | IOMUXC_SW_PAD_CTL_PAD_PUE |

src/SdFatConfig.h

 #define ENABLE_ARDUINO_SERIAL 1
 /** For Debug - must be one */
 #define ENABLE_ARDUINO_STRING 1
+//------------------------------------------------------------------------------
 /** Set USE_BLOCK_DEVICE_INTERFACE nonzero to use generic block device */
 #define USE_BLOCK_DEVICE_INTERFACE 0
 //------------------------------------------------------------------------------
 #elif defined(__arm__)
 // ARM gcc defines open flags.
 #define USE_FCNTL_H 1
+#elif defined(ESP32)
+#define USE_FCNTL_H 1
 #else  // defined(__AVR__)
 #define USE_FCNTL_H 0
 #endif  // defined(__AVR__)