From 0995cec490e62d150913789d3bdb848e8445aba9 Mon Sep 17 00:00:00 2001
From: Tim Vrakas <tim.vrakas@gmail.com>
Date: Sat, 8 Aug 2020 15:03:50 -0700
Subject: [PATCH] Allocate descriptors from local buffer, rather than using
 memalign()

---
 libraries/Adafruit_ZeroDMA/Adafruit_ZeroDMA.cpp | 13 +++++++++++--
 libraries/Adafruit_ZeroDMA/Adafruit_ZeroDMA.h   |  7 +++++++
 2 files changed, 18 insertions(+), 2 deletions(-)

diff --git a/libraries/Adafruit_ZeroDMA/Adafruit_ZeroDMA.cpp b/libraries/Adafruit_ZeroDMA/Adafruit_ZeroDMA.cpp
index 0adb78470..f89c71a88 100644
--- a/libraries/Adafruit_ZeroDMA/Adafruit_ZeroDMA.cpp
+++ b/libraries/Adafruit_ZeroDMA/Adafruit_ZeroDMA.cpp
@@ -1,5 +1,4 @@
 #include <Adafruit_ZeroDMA.h>
-#include <malloc.h> // memalign() function
 
 #include "utility/dma.h"
 static volatile uint32_t _channelMask = 0; // Bitmask of allocated channels
@@ -477,7 +476,7 @@ DmacDescriptor *Adafruit_ZeroDMA::addDescriptor(
         // (aligned_alloc() or posix_memalign()) are not currently
         // available in the version of ARM GCC in use, but this is,
         // so here we are.
-        if(!(desc = (DmacDescriptor *)memalign(16, sizeof(DmacDescriptor)))) {
+        if(!(desc = alloc_descriptor())) {
             return NULL;
         }
         DmacDescriptor *prev = &_descriptor[channel];
@@ -613,6 +612,16 @@ void Adafruit_ZeroDMA::loop(boolean flag) {
     }
 }
 
+//Alocates a descriptor from the local pool
+DmacDescriptor * Adafruit_ZeroDMA::alloc_descriptor(){
+    if(allocated * sizeof(DmacDescriptor) >= sizeof(desc_heap)){
+        return (DmacDescriptor *)(&desc_heap[0] + (allocated++) * sizeof(DmacDescriptor));
+    }else
+    {
+        return NULL;
+    }
+}
+
 // MISCELLANY --------------------------------------------------------------
 
 void Adafruit_ZeroDMA::printStatus(ZeroDMAstatus s) const {
diff --git a/libraries/Adafruit_ZeroDMA/Adafruit_ZeroDMA.h b/libraries/Adafruit_ZeroDMA/Adafruit_ZeroDMA.h
index fc8461993..d94803c3b 100644
--- a/libraries/Adafruit_ZeroDMA/Adafruit_ZeroDMA.h
+++ b/libraries/Adafruit_ZeroDMA/Adafruit_ZeroDMA.h
@@ -4,6 +4,10 @@
 #include "Arduino.h"
 #include "utility/dma.h"
 
+#ifndef DMAC_DESC_HEAP_SIZE
+#define DMAC_DESC_HEAP_SIZE 4
+#endif
+
 // Status codes returned by some DMA functions and/or held in
 // a channel's jobStatus variable.
 enum ZeroDMAstatus {
@@ -54,6 +58,8 @@ class Adafruit_ZeroDMA {
 
 
  protected:  
+  __attribute__((__aligned__(16))) uint8_t desc_heap[DMAC_DESC_HEAP_SIZE*16];
+  DmacDescriptor *            alloc_descriptor();
   uint8_t                     channel;
   volatile enum ZeroDMAstatus jobStatus;
   bool                        hasDescriptors;
@@ -61,6 +67,7 @@ class Adafruit_ZeroDMA {
   uint8_t                     peripheralTrigger;
   dma_transfer_trigger_action triggerAction;
   void                      (*callback[DMA_CALLBACK_N])(Adafruit_ZeroDMA *);
+  size_t                      allocated = 0;
 };
 
 #endif // _ADAFRUIT_ZERODMA_H_