Optimize SPI transfers

Author: sandeepmistry

cores/arduino/SERCOM.cpp

@@ -300,7 +300,7 @@ void SERCOM::setClockModeSPI(SercomSpiClockMode clockMode)
   enableSPI();
 }
 
-void SERCOM::writeDataSPI(uint8_t data)
+uint8_t SERCOM::transferDataSPI(uint8_t data)
 {
   while( sercom->SPI.INTFLAG.bit.DRE == 0 )
   {
@@ -309,15 +309,7 @@ void SERCOM::writeDataSPI(uint8_t data)
 
   sercom->SPI.DATA.bit.DATA = data; // Writing data into Data register
 
-  while( sercom->SPI.INTFLAG.bit.TXC == 0 || sercom->SPI.INTFLAG.bit.DRE == 0 )
-  {
-    // Waiting Complete Transmission
-  }
-}
-
-uint16_t SERCOM::readDataSPI()
-{
-  while( sercom->SPI.INTFLAG.bit.DRE == 0 || sercom->SPI.INTFLAG.bit.RXC == 0 )
+  while( sercom->SPI.INTFLAG.bit.RXC == 0 )
   {
     // Waiting Complete Reception
   }

cores/arduino/SERCOM.h

@@ -175,8 +175,7 @@ class SERCOM
 		SercomDataOrder getDataOrderSPI( void ) ;
 		void setBaudrateSPI(uint8_t divider) ;
 		void setClockModeSPI(SercomSpiClockMode clockMode) ;
-		void writeDataSPI(uint8_t data) ;
-		uint16_t readDataSPI( void ) ;
+		uint8_t transferDataSPI(uint8_t data) ;
 		bool isBufferOverflowErrorSPI( void ) ;
 		bool isDataRegisterEmptySPI( void ) ;
 		bool isTransmitCompleteSPI( void ) ;

libraries/SPI/SPI.cpp

@@ -187,11 +187,7 @@ void SPIClass::setClockDivider(uint8_t div)
 
 byte SPIClass::transfer(uint8_t data)
 {
-  // Writing the data
-  _p_sercom->writeDataSPI(data);
-
-  // Read data
-  return _p_sercom->readDataSPI() & 0xFF;
+  return _p_sercom->transferDataSPI(data);
 }
 
 uint16_t SPIClass::transfer16(uint16_t data) {
@@ -210,6 +206,13 @@ uint16_t SPIClass::transfer16(uint16_t data) {
   return t.val;
 }
 
+void SPIClass::transfer(void *buf, size_t count)
+{
+  uint8_t *buffer = reinterpret_cast<uint8_t *>(buf);
+  for (size_t i=0; i<count; i++)
+    *buffer++ = transfer(*buffer);
+}
+
 void SPIClass::attachInterrupt() {
   // Should be enableInterrupt()
 }

libraries/SPI/SPI.h

@@ -96,7 +96,7 @@ class SPIClass {
 
   byte transfer(uint8_t data);
   uint16_t transfer16(uint16_t data);
-  inline void transfer(void *buf, size_t count);
+  void transfer(void *buf, size_t count);
 
   // Transaction Functions
   void usingInterrupt(int interruptNumber);
@@ -132,14 +132,6 @@ class SPIClass {
   uint32_t interruptMask;
 };
 
-void SPIClass::transfer(void *buf, size_t count)
-{
-  // TODO: Optimize for faster block-transfer
-  uint8_t *buffer = reinterpret_cast<uint8_t *>(buf);
-  for (size_t i=0; i<count; i++)
-    buffer[i] = transfer(buffer[i]);
-}
-
 #if SPI_INTERFACES_COUNT > 0
   extern SPIClass SPI;
 #endif