diff --git a/atmel-samd/boards/circuitplayground_express/mpconfigboard.h b/atmel-samd/boards/circuitplayground_express/mpconfigboard.h
index 5eee39574c..243e50358c 100644
--- a/atmel-samd/boards/circuitplayground_express/mpconfigboard.h
+++ b/atmel-samd/boards/circuitplayground_express/mpconfigboard.h
@@ -12,13 +12,13 @@
 
 // Rev B:
 // #define SPI_FLASH_PAD0_PINMUX PINMUX_PA12D_SERCOM4_PAD0 // MISO
-// #define SPI_FLASH_PAD1_PINMUX PINMUX_DEFAULT // CS
+// #define SPI_FLASH_PAD1_PINMUX PINMUX_UNUSED // CS
 // #define SPI_FLASH_PAD2_PINMUX PINMUX_PB10D_SERCOM4_PAD2 // MOSI
 // #define SPI_FLASH_PAD3_PINMUX PINMUX_PB11D_SERCOM4_PAD3 // SCK
 
 // Rev C:
 #define SPI_FLASH_PAD0_PINMUX PINMUX_PA16D_SERCOM3_PAD0 // MISO
-#define SPI_FLASH_PAD1_PINMUX PINMUX_DEFAULT // CS
+#define SPI_FLASH_PAD1_PINMUX PINMUX_UNUSED // CS
 #define SPI_FLASH_PAD2_PINMUX PINMUX_PA20D_SERCOM3_PAD2 // MOSI
 #define SPI_FLASH_PAD3_PINMUX PINMUX_PA21D_SERCOM3_PAD3 // SCK
 
diff --git a/atmel-samd/boards/feather_m0_express/mpconfigboard.h b/atmel-samd/boards/feather_m0_express/mpconfigboard.h
index b18de9544e..93ec565bd0 100644
--- a/atmel-samd/boards/feather_m0_express/mpconfigboard.h
+++ b/atmel-samd/boards/feather_m0_express/mpconfigboard.h
@@ -13,7 +13,7 @@
 // Use default pinmux for the chip select since we manage it ourselves.
 #define SPI_FLASH_PAD1_PINMUX PINMUX_PA09D_SERCOM2_PAD1 // SCK
 #define SPI_FLASH_PAD2_PINMUX PINMUX_PA14C_SERCOM2_PAD2 // MISO
-#define SPI_FLASH_PAD3_PINMUX PINMUX_DEFAULT // SCK
+#define SPI_FLASH_PAD3_PINMUX PINMUX_UNUSED // SCK
 #define SPI_FLASH_SERCOM      SERCOM2
 
 #define SPI_FLASH_CS          PIN_PA13
diff --git a/atmel-samd/boards/metro_m0_express/mpconfigboard.h b/atmel-samd/boards/metro_m0_express/mpconfigboard.h
index ddee4ff70b..728169957d 100644
--- a/atmel-samd/boards/metro_m0_express/mpconfigboard.h
+++ b/atmel-samd/boards/metro_m0_express/mpconfigboard.h
@@ -12,7 +12,7 @@
 #define SPI_FLASH_BAUDRATE  (8000000)
 
 #define SPI_FLASH_MUX_SETTING SPI_SIGNAL_MUX_SETTING_F
-#define SPI_FLASH_PAD0_PINMUX PINMUX_DEFAULT // CS
+#define SPI_FLASH_PAD0_PINMUX PINMUX_UNUSED // CS
 // Use default pinmux for the chip select since we manage it ourselves.
 #define SPI_FLASH_PAD1_PINMUX PINMUX_PB03D_SERCOM5_PAD1 // MISO
 #define SPI_FLASH_PAD2_PINMUX PINMUX_PB22D_SERCOM5_PAD2 // MOSI
diff --git a/atmel-samd/common-hal/busio/SPI.c b/atmel-samd/common-hal/busio/SPI.c
index 75891c6dfd..f3f289f37c 100644
--- a/atmel-samd/common-hal/busio/SPI.c
+++ b/atmel-samd/common-hal/busio/SPI.c
@@ -29,6 +29,7 @@
 #include "py/runtime.h"
 #include "rgb_led_status.h"
 #include "samd21_pins.h"
+#include "shared_dma.h"
 
 // We use ENABLE registers below we don't want to treat as a macro.
 #undef ENABLE
@@ -127,6 +128,11 @@ void common_hal_busio_spi_construct(busio_spi_obj_t *self,
                              &config_spi_master.pinmux_pad1,
                              &config_spi_master.pinmux_pad2,
                              &config_spi_master.pinmux_pad3};
+    // Set other pinmuxes to unused so we don't accidentally change other pin
+    // state.
+    for (uint8_t i = 0; i < 4; i++) {
+        *pinmuxes[i] = PINMUX_UNUSED;
+    }
     *pinmuxes[clock_pad] = clock_pinmux;
     self->clock_pin = clock->pin;
     claim_pin(clock);
@@ -220,10 +226,12 @@ bool common_hal_busio_spi_write(busio_spi_obj_t *self,
     if (len == 0) {
         return true;
     }
-    enum status_code status = spi_write_buffer_wait(
-        &self->spi_master_instance,
-        data,
-        len);
+    enum status_code status;
+    if (len >= 16) {
+        status = shared_dma_write(self->spi_master_instance.hw, data, len);
+    } else {
+        status = spi_write_buffer_wait(&self->spi_master_instance, data, len);
+    }
     return status == STATUS_OK;
 }
 
@@ -232,10 +240,11 @@ bool common_hal_busio_spi_read(busio_spi_obj_t *self,
     if (len == 0) {
         return true;
     }
-    enum status_code status = spi_read_buffer_wait(
-        &self->spi_master_instance,
-        data,
-        len,
-        write_value);
+    enum status_code status;
+    if (len >= 16) {
+        status = shared_dma_read(self->spi_master_instance.hw, data, len, write_value);
+    } else {
+        status = spi_read_buffer_wait(&self->spi_master_instance, data, len, write_value);
+    }
     return status == STATUS_OK;
 }