Merge pull request #77 from monroewilliams/master

Faster hardware SPI writes on SAMD

Author: ladyada

Adafruit_SPIDevice.cpp

@@ -312,6 +312,22 @@ bool Adafruit_SPIDevice::write(uint8_t *buffer, size_t len,
       _spi->transferBytes(buffer, nullptr, len);
     }
   } else
+#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);
+    }
+    if (len > 0) {
+      _spi->transfer(buffer, nullptr, len);
+    }
+  } else
 #endif
   {
     for (size_t i = 0; i < prefix_len; i++) {
@@ -417,6 +433,19 @@ bool Adafruit_SPIDevice::write_then_read(uint8_t *write_buffer,
       _spi->transferBytes(write_buffer, nullptr, write_len);
     }
   } else
+#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);
+    }
+  } else
 #endif
   {
     for (size_t i = 0; i < write_len; i++) {