T4 - Async updates - Hack for high memory...

If a buffer is up in the high memory, that is either in the area marked DMARAM or created by malloc and you try to do a SPI transfer using DMA, the code detects the addresses >= 0x20200000 and then calls the system functions to either flush the cache or delete the cache on the read...

SPI.cpp

@@ -1583,6 +1583,7 @@ bool SPIClass::transfer(const void *buf, void *retbuf, size_t count, EventRespon
 	if (buf) {
 		_dmaTX->sourceBuffer((uint8_t*)write_data, count);  
 		_dmaTX->TCD->SLAST = 0;	// Finish with it pointing to next location
+		if ((uint32_t)write_data >= 0x20200000u)  arm_dcache_flush(write_data, count);
 	} else {
 		_dmaTX->source((uint8_t&)_transferWriteFill);   // maybe have setable value
 		DMAChanneltransferCount(_dmaTX, count);
@@ -1592,6 +1593,7 @@ bool SPIClass::transfer(const void *buf, void *retbuf, size_t count, EventRespon
 		_dmaRX->TCD->ATTR_SRC = 0;		//Make sure set for 8 bit mode...
 		_dmaRX->destinationBuffer((uint8_t*)retbuf, count);
 		_dmaRX->TCD->DLASTSGA = 0;		// At end point after our bufffer
+		if ((uint32_t)retbuf >= 0x20200000u)  arm_dcache_delete(retbuf, count);
 	} else {
 			// Write  only mode
 		_dmaRX->TCD->ATTR_SRC = 0;		//Make sure set for 8 bit mode...