diff --git a/NPR_14/Makefile b/NPR_14/Makefile
index bc33133..84972f0 100644
--- a/NPR_14/Makefile
+++ b/NPR_14/Makefile
@@ -249,6 +249,7 @@ OBJECTS += ./source/Eth_IPv4.o
 OBJECTS += ./source/HMI_telnet.o
 OBJECTS += ./source/L1L2_radio.o
 OBJECTS += ./source/SI4463.o
+OBJECTS += ./source/SPI_F4HDK.o
 OBJECTS += ./source/TDMA.o
 OBJECTS += ./source/Virt_Chan.o
 OBJECTS += ./source/W5500.o
diff --git a/NPR_14/source/SI4463.h b/NPR_14/source/SI4463.h
index e9f3f73..981ff2e 100644
--- a/NPR_14/source/SI4463.h
+++ b/NPR_14/source/SI4463.h
@@ -20,6 +20,7 @@
 
 #include "mbed.h"
 #include "SI4463.h"
+#include "SPI_F4HDK.h"
 
 #define SI4463_offset_size 90
 #define SI4463_CONF_RX_FIFO_threshold 90 
@@ -32,7 +33,7 @@
 //#define SI4463_zero_frame_time 590
 
 struct SI4463_Chip{
-    SPI* spi;
+    SPI_F4HDK* spi;
     DigitalOut* cs;
 	InterruptIn* interrupt;
 	int RX_TX_state; //0:nothing 1:RX 2:TX
diff --git a/NPR_14/source/SPI_F4HDK.cpp b/NPR_14/source/SPI_F4HDK.cpp
new file mode 100644
index 0000000..4ee9bf2
--- /dev/null
+++ b/NPR_14/source/SPI_F4HDK.cpp
@@ -0,0 +1,30 @@
+#include "spi_api.h"
+#include "SPI_F4HDK.h"
+
+#if DEVICE_SPI_ASYNCH
+    #define SPI_S(obj)    (( struct spi_s *)(&(obj->spi)))
+#else
+    #define SPI_S(obj)    (( struct spi_s *)(obj))
+#endif
+
+int spi_master_transfer_2(spi_t *obj, const unsigned char *tx, size_t tx_length, unsigned char *rx, size_t rx_length) {
+    struct spi_s *spiobj = SPI_S(obj);
+    SPI_HandleTypeDef *handle = &(spiobj->handle);
+
+	if(tx_length < rx_length) {
+		tx_length = rx_length;
+	}
+	
+    /*  Use 10ms timeout */
+    uint16_t ret = HAL_SPI_TransmitReceive(handle, (uint8_t *)tx, (uint8_t *)rx, tx_length, 3); //3
+
+    if(ret == HAL_OK) {
+       return tx_length;
+    } else {
+       return -1;
+    }
+}
+
+int SPI_F4HDK::transfer_2(const unsigned char *tx_buffer, int tx_length, unsigned char *rx_buffer, int rx_length) {
+	return spi_master_transfer_2 (&_spi, tx_buffer, tx_length, rx_buffer, rx_length);
+}
diff --git a/NPR_14/source/SPI_F4HDK.h b/NPR_14/source/SPI_F4HDK.h
new file mode 100644
index 0000000..f1c1d0a
--- /dev/null
+++ b/NPR_14/source/SPI_F4HDK.h
@@ -0,0 +1,21 @@
+#ifndef __SPI_F4HDK_H__
+#define __SPI_F4HDK_H__
+
+#include "mbed.h"
+#include "SPI.h"
+
+/**
+ * This class inherits from the standard SPI and adds a custom function,
+ * `transfer_2`, originally written by F4HDK. The original code directly
+ * modified the MbedOS files `SPI.h` and `stm_spi_api.c`, which is not ideal.
+ * The new approach uses inheritance in C++ to create a custom SPI class with
+ * an additional method, `transfer_2`.
+ */
+class SPI_F4HDK: public SPI {
+public:
+    using SPI::SPI;
+
+    int transfer_2(const unsigned char *tx_buffer, int tx_length, unsigned char *rx_buffer, int rx_length);
+};
+
+#endif
diff --git a/NPR_14/source/W5500.h b/NPR_14/source/W5500.h
index ef46243..49bad5d 100644
--- a/NPR_14/source/W5500.h
+++ b/NPR_14/source/W5500.h
@@ -19,9 +19,10 @@
 #define W5500_F4
 
 #include "mbed.h"
+#include "SPI_F4HDK.h"
 
 struct W5500_chip{
-    SPI* spi_port;
+    SPI_F4HDK* spi_port;
     DigitalOut* cs;
 	DigitalIn* interrupt;
 	unsigned char sock_interrupt;
diff --git a/NPR_14/source/ext_SRAM2.h b/NPR_14/source/ext_SRAM2.h
index ba4eacc..0f11c4f 100644
--- a/NPR_14/source/ext_SRAM2.h
+++ b/NPR_14/source/ext_SRAM2.h
@@ -19,9 +19,10 @@
 #define EXT_SRAM_F4
 
 #include "mbed.h"
+#include "SPI_F4HDK.h"
 
 struct ext_SRAM_chip{
-    SPI* spi_port;
+    SPI_F4HDK* spi_port;
     DigitalOut* cs;
 };
 
diff --git a/NPR_14/source/main.cpp b/NPR_14/source/main.cpp
index c341f5e..d285550 100644
--- a/NPR_14/source/main.cpp
+++ b/NPR_14/source/main.cpp
@@ -27,6 +27,7 @@
 #include "TDMA.h"
 #include "signaling.h"
 #include "config_flash.h"
+#include "SPI_F4HDK.h"
 
 #include "ext_SRAM2.h"
 
@@ -46,12 +47,12 @@ DigitalOut LED_connected(PA_12);
 
 DigitalIn Int_W5500(PA_8);
 DigitalOut CS1(PA_11);//CS W5500
-SPI spi_2(PB_5, PB_4, PB_3); // mosi, miso, sclk
+SPI_F4HDK spi_2(PB_5, PB_4, PB_3); // mosi, miso, sclk
 DigitalOut CS3(PB_0);// CS ext SRAM PB_0 
 
 InterruptIn Int_SI4463(PA_3);
 DigitalOut CS2(PA_4);
-SPI spi_1(PA_7, PA_6, PA_5); // mosi, miso, sclk
+SPI_F4HDK spi_1(PA_7, PA_6, PA_5); // mosi, miso, sclk
 
 int main()
 {