both samd21/d51 works perfectly with max3421e

hw/bsp/samd21/boards/metro_m0_express/board.h

@@ -43,6 +43,22 @@
 #define UART_RX_PIN           4
 #define UART_TX_PIN           5
 
+// SPI for USB host shield
+#define MAX3421_SERCOM_ID       4       // SERCOM4
+#define MAX3421_SERCOM_FUNCTION 3       // function D (Sercom Alt)
+
+#define MAX3421_SCK_PIN         (32+11)
+#define MAX3421_MOSI_PIN        (32+10)
+#define MAX3421_MISO_PIN        12
+#define MAX3421_TX_PAD          1 // MOSI = PAD_2, SCK = PAD_3
+#define MAX3421_RX_PAD          0 // MISO = PAD_2
+
+#define MAX3421_CS_PIN          18      // D10
+
+#define MAX3421_INTR_PIN        7       // D9
+#define MAX3421_INTR_EIC_ID     7       // EIC7
+
+
 #ifdef __cplusplus
  }
 #endif