Add full duplex capability to SPI

Also fixed the no-return error within 'transfer' and added last-resort definitions of 'SS' 'MOSI' 'MISO' and 'CLK' to ensure out-of-the-box compatibility with the SD examples.

Author: oclyke

cores/arduino/ard_sup/Arduino.h

@@ -83,4 +83,6 @@ extern "C"
 
 #include "variant.h"
 
+#include "ap3_post_variant.h"
+
 #endif // _ARDUINO_H_

cores/arduino/ard_sup/ap3_post_variant.h

@@ -0,0 +1,23 @@
+#ifndef _AP3_POST_VARIANT_H_
+#define _AP3_POST_VARIANT_H_
+
+// Some fail-unsafe defines for SD card library compilation. 
+// These ideally would be defined in a variant header, however
+// if they are not these definitions may suffice
+#ifndef SS
+#define SS 50
+#endif  // SS
+#ifndef MOSI
+#define MOSI 50
+#endif  // SS
+#ifndef MISO
+#define MISO 50
+#endif  // SS
+#ifndef CLK
+#define CLK 50
+#endif  // SS
+
+
+
+
+#endif // _AP3_POST_VARIANT_H_

libraries/SPI/src/SPI.cpp

@@ -225,7 +225,9 @@ void SPIClass::setDataMode(uint8_t mode)
 
 byte SPIClass::transfer(uint8_t data)
 {
-  _transfer(&data, NULL, 1);
+  uint8_t rxval = 0x00;
+  _transfer(&data, &rxval, 1);
+  return rxval;
 }
 
 uint16_t SPIClass::transfer16(uint16_t data)
@@ -289,7 +291,7 @@ void SPIClass::_transfer(void *buf_out, void *buf_in, size_t count)
   // Determine direction
   if ((buf_out != NULL) && (buf_in != NULL))
   {
-    iomTransfer.eDirection = AM_HAL_IOM_TX; // AM_HAL_IOM_FULLDUPLEX - Note: Ambiq SDK says that FULLDUPLEX is not yet supported // todo:
+    iomTransfer.eDirection = AM_HAL_IOM_FULLDUPLEX;
   }
   else if (buf_out != NULL)
   {
@@ -300,12 +302,18 @@ void SPIClass::_transfer(void *buf_out, void *buf_in, size_t count)
     iomTransfer.eDirection = AM_HAL_IOM_RX;
   }
 
-  uint32_t retVal32 = am_hal_iom_blocking_transfer(_handle, &iomTransfer);
-  if (retVal32 != 0)
-  {
-    // Serial.printf("got an error on _transfer: %d\n", retVal32);
-    return /*retVal32*/;
+  uint32_t retVal32 = 0;
+  if( iomTransfer.eDirection == AM_HAL_IOM_FULLDUPLEX ){
+    retVal32 = am_hal_iom_spi_blocking_fullduplex(_handle, &iomTransfer);
+  }else{
+    retVal32 = am_hal_iom_blocking_transfer(_handle, &iomTransfer);
   }
+   
+  // if (retVal32 != 0)
+  // {
+  //   Serial.printf("got an error on _transfer: %d\n", retVal32);
+  //   return retVal32;
+  // }
 }
 
 void SPIClass::attachInterrupt()