Allow unaligned input/output to SPI::transferBytes

libraries/SPI/SPI.cpp

@@ -509,9 +509,6 @@ void SPIClass::writePattern(const uint8_t * data, uint8_t size, uint32_t repeat)
 }
 
 /**
- * Note:
- *  in and out need to be aligned to 32Bit
- *  or you get an Fatal exception (9)
  * @param out uint8_t *
  * @param in  uint8_t *
  * @param size uint32_t
@@ -538,45 +535,83 @@ void SPIClass::transferBytes(const uint8_t * out, uint8_t * in, uint32_t size) {
  * @param in  uint8_t *
  * @param size uint8_t (max 64)
  */
-void SPIClass::transferBytes_(const uint8_t * out, uint8_t * in, uint8_t size) {
+
+void SPIClass::transferBytesAligned_(const uint8_t * out, uint8_t * in, uint8_t size) {
+    if (!size)
+        return;
+
     while(SPI1CMD & SPIBUSY) {}
     // Set in/out Bits to transfer
 
     setDataBits(size * 8);
 
-    volatile uint32_t * fifoPtr = &SPI1W0;
-    uint8_t dataSize = ((size + 3) / 4);
+    volatile uint32_t *fifoPtr = &SPI1W0;
 
-    if(out) {
-        uint32_t * dataPtr = (uint32_t*) out;
-        while(dataSize--) {
-            *fifoPtr = *dataPtr;
-            dataPtr++;
-            fifoPtr++;
+    if (out) {
+        uint8_t outSize = ((size + 3) / 4);
+        uint32_t *dataPtr = (uint32_t*) out;
+        while (outSize--) {
+            *(fifoPtr++) = *(dataPtr++);
         }
     } else {
+        uint8_t outSize = ((size + 3) / 4);
         // no out data only read fill with dummy data!
-        while(dataSize--) {
-            *fifoPtr = 0xFFFFFFFF;
-            fifoPtr++;
+        while (outSize--) {
+            *(fifoPtr++) = 0xFFFFFFFF;
         }
     }
 
     SPI1CMD |= SPIBUSY;
     while(SPI1CMD & SPIBUSY) {}
 
-    if(in) {
-        uint32_t * dataPtr = (uint32_t*) in;
+    if (in) {
+        uint32_t *dataPtr = (uint32_t*) in;
         fifoPtr = &SPI1W0;
-        dataSize = ((size + 3) / 4);
-        while(dataSize--) {
-            *dataPtr = *fifoPtr;
-            dataPtr++;
-            fifoPtr++;
+        int inSize = size;
+        // Unlike outSize above, inSize tracks *bytes* since we must transfer only the requested bytes to the app to avoid overwriting other vars.
+        while (inSize >= 4) {
+            *(dataPtr++) = *(fifoPtr++);
+            inSize -= 4;
+            in += 4;
         }
+        volatile uint8_t *fifoPtrB = (volatile uint8_t *)fifoPtr;
+        while (inSize--) {
+            *(in++) = *(fifoPtrB++);
+        }
+    }
+}
+
+
+void SPIClass::transferBytes_(const uint8_t * out, uint8_t * in, uint8_t size) {
+    if (!((uint32_t)out & 3) && !((uint32_t)in & 3)) {
+        // Input and output are both 32b aligned or NULL
+        transferBytesAligned_(out, in, size);
+    } else if (!out) {
+        // Input only and misaligned, do bytewise until in aligned
+        while (size && ((uint32_t)in & 3)) {
+            *(in++) = transfer(0xff);
+            size--;
+        }
+        transferBytesAligned_(out, in, size);
+    } else if (!in) {
+        // Output only and misaligned, bytewise xmit until aligned
+        while (size && ((uint32_t)out & 3)) {
+            transfer(*(out++));
+            size--;
+        }
+        transferBytesAligned_(out, in, size);
+    } else {
+        // HW FIFO has 64b limit and ::transferBytes breaks up large xfers into 64byte chunks before calling this function
+        // We know at this point it is a bidirectional transfer
+        uint8_t aligned[64]; // Stack vars will be 32b aligned
+        // No need for separate out and in aligned copies, we can overwrite our out copy with the input data safely
+        memcpy(aligned, out, size);
+        transferBytesAligned_(aligned, aligned, size);
+        memcpy(in, aligned, size);
     }
 }
 
+
 #if !defined(NO_GLOBAL_INSTANCES) && !defined(NO_GLOBAL_SPI)
 SPIClass SPI;
 #endif

libraries/SPI/SPI.h

@@ -79,6 +79,7 @@ class SPIClass {
   uint8_t pinSet;
   void writeBytes_(const uint8_t * data, uint8_t size);
   void transferBytes_(const uint8_t * out, uint8_t * in, uint8_t size);
+  void transferBytesAligned_(const uint8_t * out, uint8_t * in, uint8_t size);
   inline void setDataBits(uint16_t bits);
 };