SPI DMA still WIP still not working

Author: PaintYourDragon

libraries/Adafruit_ZeroDMA/Adafruit_ZeroDMA.cpp

@@ -250,7 +250,7 @@ ZeroDMAstatus Adafruit_ZeroDMA::allocate(void) {
     return DMA_STATUS_OK;
 }
 
-void Adafruit_ZeroDMA::setPriority(dma_priority pri) {
+void Adafruit_ZeroDMA::setPriority(dma_priority pri) const {
 #ifdef __SAMD51__
     DMAC->Channel[channel].CHPRILVL.bit.PRILVL = pri;
 #else
@@ -341,7 +341,7 @@ void Adafruit_ZeroDMA::setCallback(
 }
 
 // Suspend/resume don't quite do what I thought -- avoid using for now.
-void Adafruit_ZeroDMA::suspend(void) {
+void Adafruit_ZeroDMA::suspend(void) const {
     cpu_irq_enter_critical();
 #ifdef __SAMD51__
     DMAC->Channel[channel].CHCTRLB.reg |= DMAC_CHCTRLB_CMD_SUSPEND;
@@ -428,12 +428,17 @@ void Adafruit_ZeroDMA::setAction(dma_transfer_trigger_action action) {
 }
 
 // Issue software trigger. Channel must be allocated & descriptors added!
-void Adafruit_ZeroDMA::trigger(void) {
+void Adafruit_ZeroDMA::trigger(void) const {
     if((channel <= DMAC_CH_NUM) & hasDescriptors) {
         DMAC->SWTRIGCTRL.reg |= (1 << channel);
     }
 }
 
+// Returns true if DMA transfer in progress.
+bool Adafruit_ZeroDMA::isActive(void) const {
+    return _writeback[channel].BTCTRL.bit.VALID;
+}
+
 // DMA DESCRIPTOR FUNCTIONS ------------------------------------------------
 
 // Allocates a new DMA descriptor (if needed) and appends it to the
@@ -610,7 +615,7 @@ void Adafruit_ZeroDMA::loop(boolean flag) {
 
 // MISCELLANY --------------------------------------------------------------
 
-void Adafruit_ZeroDMA::printStatus(ZeroDMAstatus s) {
+void Adafruit_ZeroDMA::printStatus(ZeroDMAstatus s) const {
     if(s == DMA_STATUS_JOBSTATUS) s = jobStatus;
     Serial.print("Status: ");
     switch(s) {

libraries/Adafruit_ZeroDMA/Adafruit_ZeroDMA.h

@@ -48,12 +48,10 @@ class Adafruit_ZeroDMA {
                     bool stepSel = DMA_STEPSEL_DST);
   void            changeDescriptor(DmacDescriptor *d, void *src = NULL,
                     void *dst = NULL, uint32_t count = 0);
+  bool            isActive(void) const;
 
   void            _IRQhandler(uint8_t flags); // DO NOT TOUCH
 
-  bool            isActive(void) const {
-                    return _writeback[channel].BTCTRL.bit.VALID;
-                  }
 
  protected:  
   uint8_t                     channel;

libraries/SPI/SPI.cpp

@@ -277,7 +277,7 @@ void SPIClass::transfer(const void* txbuf, void* rxbuf, size_t count,
         if(writeChannel.allocate() == DMA_STATUS_OK) {
             writeDescriptor =
               writeChannel.addDescriptor(
-                (void *)NULL,              // Source address (set later)
+                NULL,                      // Source address (set later)
                 (void *)getDataRegister(), // Dest (SPI data register)
                 0,                         // Count (set later)
                 DMA_BEAT_SIZE_BYTE,        // Bytes/hwords/words
@@ -290,11 +290,11 @@ void SPIClass::transfer(const void* txbuf, void* rxbuf, size_t count,
         }
     }
 
-    if(writeDescriptor) { // If this allocated, then use DMA
-        static uint8_t dum = 0xFF; // Dummy byte for read-only transfers
+    if(writeDescriptor && (readDescriptor || !rxbuf)) {
+        static const uint8_t dum = 0xFF; // Dummy byte for read-only xfers
 
-        // Initialize read descriptor dest address to rxbuf (even if unused)
-        readDescriptor->DSTADDR.reg = (uint32_t)rxbuf;
+        // Initialize read descriptor dest address to rxbuf (even if NULL)
+        if(readDescriptor) readDescriptor->DSTADDR.reg = (uint32_t)rxbuf;
 
         // If reading only, set up writeDescriptor to issue dummy bytes
         // (set SRCADDR to &dum and SRCINC to 0). Otherwise, set SRCADDR