diff --git a/cores/esp32/esp32-hal-spi.c b/cores/esp32/esp32-hal-spi.c
index d28abf4a5ba..9dfe34cb8e0 100644
--- a/cores/esp32/esp32-hal-spi.c
+++ b/cores/esp32/esp32-hal-spi.c
@@ -459,7 +459,7 @@ void spiWaitReady(spi_t * spi)
     while(spi->dev->cmd.usr);
 }
 
-void spiWrite(spi_t * spi, uint32_t *data, uint8_t len)
+void spiWrite(spi_t * spi, const uint32_t *data, uint8_t len)
 {
     if(!spi) {
         return;
@@ -671,7 +671,7 @@ void __spiTransferBytes(spi_t * spi, uint8_t * data, uint8_t * out, uint32_t byt
     }
 }
 
-void spiTransferBytes(spi_t * spi, uint8_t * data, uint8_t * out, uint32_t size)
+void spiTransferBytes(spi_t * spi, const uint8_t * data, uint8_t * out, uint32_t size)
 {
     if(!spi) {
         return;
@@ -861,7 +861,7 @@ uint32_t spiTransferLongNL(spi_t * spi, uint32_t data)
     return data;
 }
 
-void spiWriteNL(spi_t * spi, const void * data_in, size_t len){
+void spiWriteNL(spi_t * spi, const void * data_in, uint32_t len){
     size_t longs = len >> 2;
     if(len & 3){
         longs++;
@@ -887,7 +887,7 @@ void spiWriteNL(spi_t * spi, const void * data_in, size_t len){
     }
 }
 
-void spiTransferBytesNL(spi_t * spi, const void * data_in, uint8_t * data_out, size_t len){
+void spiTransferBytesNL(spi_t * spi, const void * data_in, uint8_t * data_out, uint32_t len){
     if(!spi) {
         return;
     }
@@ -974,7 +974,7 @@ void spiTransferBitsNL(spi_t * spi, uint32_t data, uint32_t * out, uint8_t bits)
     }
 }
 
-void IRAM_ATTR spiWritePixelsNL(spi_t * spi, const void * data_in, size_t len){
+void IRAM_ATTR spiWritePixelsNL(spi_t * spi, const void * data_in, uint32_t len){
     size_t longs = len >> 2;
     if(len & 3){
         longs++;
diff --git a/cores/esp32/esp32-hal-spi.h b/cores/esp32/esp32-hal-spi.h
index 78ef10fa3dd..1317f38b239 100644
--- a/cores/esp32/esp32-hal-spi.h
+++ b/cores/esp32/esp32-hal-spi.h
@@ -96,7 +96,7 @@ void spiSetClockDiv(spi_t * spi, uint32_t clockDiv);
 void spiSetDataMode(spi_t * spi, uint8_t dataMode);
 void spiSetBitOrder(spi_t * spi, uint8_t bitOrder);
 
-void spiWrite(spi_t * spi, uint32_t *data, uint8_t len);
+void spiWrite(spi_t * spi, const uint32_t *data, uint8_t len);
 void spiWriteByte(spi_t * spi, uint8_t data);
 void spiWriteWord(spi_t * spi, uint16_t data);
 void spiWriteLong(spi_t * spi, uint32_t data);
@@ -105,7 +105,7 @@ void spiTransfer(spi_t * spi, uint32_t *out, uint8_t len);
 uint8_t spiTransferByte(spi_t * spi, uint8_t data);
 uint16_t spiTransferWord(spi_t * spi, uint16_t data);
 uint32_t spiTransferLong(spi_t * spi, uint32_t data);
-void spiTransferBytes(spi_t * spi, uint8_t * data, uint8_t * out, uint32_t size);
+void spiTransferBytes(spi_t * spi, const uint8_t * data, uint8_t * out, uint32_t size);
 void spiTransferBits(spi_t * spi, uint32_t data, uint32_t * out, uint8_t bits);
 
 /*
@@ -115,11 +115,11 @@ void spiTransaction(spi_t * spi, uint32_t clockDiv, uint8_t dataMode, uint8_t bi
 void spiSimpleTransaction(spi_t * spi);
 void spiEndTransaction(spi_t * spi);
 
-void spiWriteNL(spi_t * spi, const void * data, uint32_t len);
+void spiWriteNL(spi_t * spi, const void * data_in, uint32_t len);
 void spiWriteByteNL(spi_t * spi, uint8_t data);
 void spiWriteShortNL(spi_t * spi, uint16_t data);
 void spiWriteLongNL(spi_t * spi, uint32_t data);
-void spiWritePixelsNL(spi_t * spi, const void * data, uint32_t len);
+void spiWritePixelsNL(spi_t * spi, const void * data_in, uint32_t len);
 
 #define spiTransferNL(spi, data, len) spiTransferBytesNL(spi, data, data, len)
 uint8_t spiTransferByteNL(spi_t * spi, uint8_t data);
diff --git a/libraries/SPI/src/SPI.cpp b/libraries/SPI/src/SPI.cpp
index 7f2977572ec..beebe0ea5a3 100644
--- a/libraries/SPI/src/SPI.cpp
+++ b/libraries/SPI/src/SPI.cpp
@@ -238,7 +238,7 @@ void SPIClass::writePixels(const void * data, uint32_t size)
  * @param out  uint8_t * output buffer. can be NULL for Write Only operation
  * @param size uint32_t
  */
-void SPIClass::transferBytes(uint8_t * data, uint8_t * out, uint32_t size)
+void SPIClass::transferBytes(const uint8_t * data, uint8_t * out, uint32_t size)
 {
     if(_inTransaction){
         return spiTransferBytesNL(_spi, data, out, size);
@@ -251,7 +251,7 @@ void SPIClass::transferBytes(uint8_t * data, uint8_t * out, uint32_t size)
  * @param size uint8_t  max for size is 64Byte
  * @param repeat uint32_t
  */
-void SPIClass::writePattern(uint8_t * data, uint8_t size, uint32_t repeat)
+void SPIClass::writePattern(const uint8_t * data, uint8_t size, uint32_t repeat)
 {
     if(size > 64) {
         return;    //max Hardware FIFO
@@ -272,12 +272,12 @@ void SPIClass::writePattern(uint8_t * data, uint8_t size, uint32_t repeat)
     }
 }
 
-void SPIClass::writePattern_(uint8_t * data, uint8_t size, uint8_t repeat)
+void SPIClass::writePattern_(const uint8_t * data, uint8_t size, uint8_t repeat)
 {
     uint8_t bytes = (size * repeat);
     uint8_t buffer[64];
     uint8_t * bufferPtr = &buffer[0];
-    uint8_t * dataPtr;
+    const uint8_t * dataPtr;
     uint8_t dataSize = bytes;
     for(uint8_t i = 0; i < repeat; i++) {
         dataSize = size;
diff --git a/libraries/SPI/src/SPI.h b/libraries/SPI/src/SPI.h
index e34833bd435..416fb363290 100644
--- a/libraries/SPI/src/SPI.h
+++ b/libraries/SPI/src/SPI.h
@@ -48,7 +48,7 @@ class SPIClass
     uint32_t _div;
     uint32_t _freq;
     bool _inTransaction;
-    void writePattern_(uint8_t * data, uint8_t size, uint8_t repeat);
+    void writePattern_(const uint8_t * data, uint8_t size, uint8_t repeat);
 
 public:
     SPIClass(uint8_t spi_bus=HSPI);
@@ -70,7 +70,7 @@ class SPIClass
     uint16_t transfer16(uint16_t data);
     uint32_t transfer32(uint32_t data);
   
-    void transferBytes(uint8_t * data, uint8_t * out, uint32_t size);
+    void transferBytes(const uint8_t * data, uint8_t * out, uint32_t size);
     void transferBits(uint32_t data, uint32_t * out, uint8_t bits);
 
     void write(uint8_t data);
@@ -78,7 +78,7 @@ class SPIClass
     void write32(uint32_t data);
     void writeBytes(const uint8_t * data, uint32_t size);
     void writePixels(const void * data, uint32_t size);//ili9341 compatible
-    void writePattern(uint8_t * data, uint8_t size, uint32_t repeat);
+    void writePattern(const uint8_t * data, uint8_t size, uint32_t repeat);
 
     spi_t * bus(){ return _spi; }
 };