Fix ESP8266 DMA off-by-one

Shim in https://github.com/Makuna/NeoPixelBus/pull/894 until approved by
upstream.  Fixes #4906 and #5136.

lib/NeoESP8266DMAFix/include/NeoEsp8266DmaMethodFix.h

@@ -0,0 +1,122 @@
+/*-------------------------------------------------------------------------
+NeoPixel library helper functions for Esp8266.
+
+FIXED VERSION FROM https://github.com/Makuna/NeoPixelBus/pull/894
+This library will overlay/shadow the base version from NeoPixelBus 
+
+Written by Michael C. Miller.
+Thanks to g3gg0.de for porting the initial DMA support which lead to this.
+Thanks to github/cnlohr for the original work on DMA support, which opend
+all our minds to a better way (located at https://github.com/cnlohr/esp8266ws2812i2s).
+
+I invest time and resources providing this open source code,
+please support me by donating (see https://github.com/Makuna/NeoPixelBus)
+
+-------------------------------------------------------------------------
+This file is part of the Makuna/NeoPixelBus library.
+
+NeoPixelBus is free software: you can redistribute it and/or modify
+it under the terms of the GNU Lesser General Public License as
+published by the Free Software Foundation, either version 3 of
+the License, or (at your option) any later version.
+
+NeoPixelBus is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU Lesser General Public License for more details.
+
+You should have received a copy of the GNU Lesser General Public
+License along with NeoPixel.  If not, see
+<http://www.gnu.org/licenses/>.
+-------------------------------------------------------------------------*/
+
+#pragma once
+
+#ifdef ARDUINO_ARCH_ESP8266
+#include "internal/methods/NeoEsp8266DmaMethod.h"
+
+template<typename T_PATTERN> class NeoEsp8266Dma3StepEncodeFixed : public T_PATTERN
+{
+public:
+    const static size_t DmaBitsPerPixelBit = 3; // 3 step cadence, matches encoding
+
+    static size_t SpacingPixelSize(size_t sizePixel)
+    {
+        return sizePixel;
+    }
+
+    static void FillBuffers(uint8_t* i2sBuffer,
+        const uint8_t* data,
+        size_t sizeData,
+        [[maybe_unused]] size_t sizePixel)
+    {
+        const uint8_t SrcBitMask = 0x80;
+        const size_t BitsInSample = sizeof(uint32_t) * 8;
+
+        uint32_t* pDma = reinterpret_cast<uint32_t*>(i2sBuffer);
+        uint32_t dmaValue = 0;
+        uint8_t destBitsLeft = BitsInSample;
+
+        const uint8_t* pSrc = data;
+        const uint8_t* pEnd = pSrc + sizeData;
+
+        while (pSrc < pEnd)
+        {
+            uint8_t value = *(pSrc++);
+
+            for (uint8_t bitSrc = 0; bitSrc < 8; bitSrc++)
+            {
+                const uint16_t Bit = ((value & SrcBitMask) ? T_PATTERN::OneBit3Step : T_PATTERN::ZeroBit3Step);
+
+                if (destBitsLeft > 3)
+                {
+                    destBitsLeft -= 3;
+                    dmaValue |= Bit << destBitsLeft;
+
+#if defined(NEO_DEBUG_DUMP_I2S_BUFFER)
+                    NeoUtil::PrintBin<uint32_t>(dmaValue);
+                    Serial.print(" < ");
+                    Serial.println(destBitsLeft);
+#endif
+                }
+                else if (destBitsLeft <= 3)
+                {
+                    uint8_t bitSplit = (3 - destBitsLeft);
+                    dmaValue |= Bit >> bitSplit;
+
+#if defined(NEO_DEBUG_DUMP_I2S_BUFFER)
+                    NeoUtil::PrintBin<uint32_t>(dmaValue);
+                    Serial.print(" > ");
+                    Serial.println(bitSplit);
+#endif
+                    // next dma value, store and reset
+                    *(pDma++) = dmaValue;
+                    dmaValue = 0;
+
+                    destBitsLeft = BitsInSample - bitSplit;
+                    if (bitSplit)
+                    {
+                        dmaValue |= Bit << destBitsLeft;
+                    }
+
+#if defined(NEO_DEBUG_DUMP_I2S_BUFFER)
+                    NeoUtil::PrintBin<uint32_t>(dmaValue);
+                    Serial.print(" v ");
+                    Serial.println(bitSplit);
+#endif
+                }
+
+                // Next
+                value <<= 1;
+            }
+        }
+        // store the remaining bits
+        if (destBitsLeft != BitsInSample) *pDma++ = dmaValue;
+    }
+};
+
+// Abuse explict specialization to overlay the methods
+template<> class NeoEsp8266Dma3StepEncode<NeoEsp8266DmaNormalPattern> : public NeoEsp8266Dma3StepEncodeFixed<NeoEsp8266DmaNormalPattern> {};
+template<> class NeoEsp8266Dma3StepEncode<NeoEsp8266DmaInvertedPattern> : public NeoEsp8266Dma3StepEncodeFixed<NeoEsp8266DmaInvertedPattern> {};
+
+#endif

lib/NeoESP8266DMAFix/library.json

@@ -0,0 +1,12 @@
+{
+  "name": "NeoESP8266DMAFix",
+  "build": { "libArchive": false },
+  "platforms": ["espressif8266"],
+  "dependencies": [
+    {
+      "owner": "makuna",      
+      "name": "NeoPixelBus",
+      "version": "2.8.3"
+    }
+  ]
+}