   }
 
   Serial.printf("Creating %dKB file, may take a while...\n", TESTSIZEKB);
-  long start = millis();
+  unsigned long start = millis();
   File f = fs->open("/testwrite.bin", "w");
   if (!f) {
     Serial.printf("Unable to open file for writing, aborting\n");

  }
  f.close();
  stop = millis();
  Serial.printf("==> Time to read 64KB in 1b chunks = %ld milliseconds = %ld bytes/s\n", stop - start, 65536 / (stop - start) * 1000);


}

void setup() {

  }
  f.close();
  stop = millis();
  Serial.printf("==> Time to read %dKB in reverse in 256b chunks = %lu milliseconds = %s\n", TESTSIZEKB, stop - start, rate(start, stop, TESTSIZEKB * 1024));

  Serial.printf("Writing 64K file in 1-byte chunks\n");
  start = millis();
