Add a hack to work around the differences between the Adafruit SAMD core and the official Arduino SAMD core.

Author: monroewilliams

Adafruit_SPIDevice.cpp

@@ -310,7 +310,14 @@ bool Adafruit_SPIDevice::write(uint8_t *buffer, size_t len,
       _spi->transferBytes(buffer, nullptr, len);
     }
   } else
-#elif defined(ARDUINO_ARCH_SAMD)
+#elif defined(ARDUINO_ARCH_SAMD) && defined(_ADAFRUIT_ZERODMA_H_)
+  // The variant of transfer() used below currently only exists in the Adafruit core.
+  // It causes a build failure when building against the main Arduino SAMD core.
+  // Unfortunately there doesn't seem to be a supported #define that this code
+  // can use to tell which core it's building against. This hack
+  // (checking for the include guard that gets defined when the Adafruit core's
+  // SPI.h includes Adafruit_ZeroDMA.h) works for now, but it should be improved
+  // when possible.
   if (_spi) {
     if (prefix_len > 0) {
       _spi->transfer(prefix_buffer, nullptr, prefix_len);
@@ -423,7 +430,14 @@ bool Adafruit_SPIDevice::write_then_read(uint8_t *write_buffer,
       _spi->transferBytes(write_buffer, nullptr, write_len);
     }
   } else
-#elif defined(ARDUINO_ARCH_SAMD)
+#elif defined(ARDUINO_ARCH_SAMD) && defined(_ADAFRUIT_ZERODMA_H_)
+  // The variant of transfer() used below currently only exists in the Adafruit core.
+  // It causes a build failure when building against the main Arduino SAMD core.
+  // Unfortunately there doesn't seem to be a supported #define that this code
+  // can use to tell which core it's building against. This hack
+  // (checking for the include guard that gets defined when the Adafruit core's
+  // SPI.h includes Adafruit_ZeroDMA.h) works for now, but it should be improved
+  // when possible.
   if (_spi) {
     if (write_len > 0) {
       _spi->transfer(write_buffer, nullptr, write_len);