diff --git a/Software/VNA_embedded/.cproject b/Software/VNA_embedded/.cproject
index 486deae..ed61843 100644
--- a/Software/VNA_embedded/.cproject
+++ b/Software/VNA_embedded/.cproject
@@ -151,6 +151,8 @@
                                     									
                                     <listOptionValue builtIn="false" value="../Inc"/>
                                     									
+                                    <listOptionValue builtIn="false" value="&quot;${workspace_loc:/${ProjName}/Application/Drivers/FPGA}&quot;"/>
+                                    									
                                     <listOptionValue builtIn="false" value="&quot;${workspace_loc:/${ProjName}/Application}&quot;"/>
                                     									
                                     <listOptionValue builtIn="false" value="&quot;${workspace_loc:/${ProjName}/Application/Drivers}&quot;"/>
@@ -185,6 +187,8 @@
                                     									
                                     <listOptionValue builtIn="false" value="USE_FULL_LL_DRIVER"/>
                                     									
+                                    <listOptionValue builtIn="false" value="HW_REVISION='B'"/>
+                                    									
                                     <listOptionValue builtIn="false" value="__weak=&quot;__attribute__((weak))&quot;"/>
                                     									
                                     <listOptionValue builtIn="false" value="USBPD_PORT_COUNT=1"/>
diff --git a/Software/VNA_embedded/Application/App.cpp b/Software/VNA_embedded/Application/App.cpp
index c8d9602..6e09120 100644
--- a/Software/VNA_embedded/Application/App.cpp
+++ b/Software/VNA_embedded/Application/App.cpp
@@ -5,12 +5,11 @@
 #include "Communication.h"
 #include "main.h"
 #include "Exti.hpp"
-#include "FPGA.hpp"
+#include "FPGA/FPGA.hpp"
 #include <complex>
 #include <cstring>
 #include "USB/usb.h"
 #include "Flash.hpp"
-#include "Firmware.hpp"
 #include "FreeRTOS.h"
 #include "task.h"
 
@@ -28,12 +27,17 @@ static Protocol::PacketInfo packet;
 static TaskHandle_t handle;
 
 // TODO set proper values
-#define HW_REVISION			'A'
+//#define HW_REVISION			'A'
 #define FW_MAJOR			0
 #define FW_MINOR			01
 
+#if HW_REVISION >= 'B'
+// has MCU controllable flash chip, firmware update supported
+#define HAS_FLASH
+#include "Firmware.hpp"
 extern SPI_HandleTypeDef hspi1;
 static Flash flash = Flash(&hspi1, FLASH_CS_GPIO_Port, FLASH_CS_Pin);
+#endif
 
 #define FLAG_USB_PACKET		0x01
 #define FLAG_DATAPOINT		0x02
@@ -67,6 +71,7 @@ void App_Start() {
 	Log_SetRedirect(usb_log);
 	LOG_INFO("Start");
 	Exti::Init();
+#ifdef HAS_FLASH
 	if(!flash.isPresent()) {
 		LOG_CRIT("Failed to detect onboard FLASH");
 	}
@@ -80,10 +85,19 @@ void App_Start() {
 	} else {
 		LOG_CRIT("Invalid bitstream/firmware, not configuring FPGA");
 	}
+#else
+	// The FPGA configures itself from the flash, allow time for this
+	vTaskDelay(2000);
+#endif
 	if (!VNA::Init()) {
 		LOG_CRIT("Initialization failed, unable to start");
 	}
 
+#if HW_REVISION == 'A'
+	// Allow USB enumeration
+	USB_EN_GPIO_Port->BSRR = USB_EN_Pin;
+#endif
+
 	uint32_t lastNewPoint = HAL_GetTick();
 	bool sweepActive = false;
 
@@ -180,25 +194,23 @@ void App_Start() {
 					manual = packet.manual;
 					VNA::ConfigureManual(manual, VNAStatusCallback);
 					break;
+#ifdef HAS_FLASH
 				case Protocol::PacketType::ClearFlash:
 					FPGA::AbortSweep();
 					sweepActive = false;
 					LOG_DEBUG("Erasing FLASH in preparation for firmware update...");
 					if(flash.eraseChip()) {
 						LOG_DEBUG("...FLASH erased")
-						Protocol::PacketInfo p;
-						p.type = Protocol::PacketType::Ack;
-						Communication::Send(p);
+						Communication::SendWithoutPayload(Protocol::PacketType::Ack);
 					} else {
 						LOG_ERR("Failed to erase FLASH");
+						Communication::SendWithoutPayload(Protocol::PacketType::Nack);
 					}
 					break;
 				case Protocol::PacketType::FirmwarePacket:
 					LOG_INFO("Writing firmware packet at address %u", packet.firmware.address);
 					flash.write(packet.firmware.address, sizeof(packet.firmware.data), packet.firmware.data);
-					Protocol::PacketInfo p;
-					p.type = Protocol::PacketType::Ack;
-					Communication::Send(p);
+					Communication::SendWithoutPayload(Protocol::PacketType::Ack);
 					break;
 				case Protocol::PacketType::PerformFirmwareUpdate: {
 					auto fw_info = Firmware::GetFlashContentInfo(&flash);
@@ -209,12 +221,15 @@ void App_Start() {
 						// Some delay to allow communication to finish
 						vTaskDelay(1000);
 						Firmware::PerformUpdate(&flash);
-						// will never get here
+						// should never get here
+						Communication::SendWithoutPayload(Protocol::PacketType::Nack);
 					}
 				}
 					break;
+#endif
 				default:
-					// ignore all other packets
+					// this packet type is not supported
+					Communication::SendWithoutPayload(Protocol::PacketType::Nack);
 					break;
 				}
 			}
diff --git a/Software/VNA_embedded/Application/Communication/Communication.cpp b/Software/VNA_embedded/Application/Communication/Communication.cpp
index 9b9b64e..0fb7122 100644
--- a/Software/VNA_embedded/Application/Communication/Communication.cpp
+++ b/Software/VNA_embedded/Application/Communication/Communication.cpp
@@ -63,3 +63,8 @@ void communication_usb_input(const uint8_t *buf, uint16_t len) {
 	Communication::Input(buf, len);
 }
 
+bool Communication::SendWithoutPayload(Protocol::PacketType type) {
+	Protocol::PacketInfo p;
+	p.type = type;
+	return Send(p);
+}
diff --git a/Software/VNA_embedded/Application/Communication/Communication.h b/Software/VNA_embedded/Application/Communication/Communication.h
index d7fbd4d..1db380c 100644
--- a/Software/VNA_embedded/Application/Communication/Communication.h
+++ b/Software/VNA_embedded/Application/Communication/Communication.h
@@ -13,6 +13,7 @@ using Callback = void(*)(Protocol::PacketInfo);
 void SetCallback(Callback cb);
 void Input(const uint8_t *buf, uint16_t len);
 bool Send(Protocol::PacketInfo packet);
+bool SendWithoutPayload(Protocol::PacketType type);
 
 }
 
diff --git a/Software/VNA_embedded/Application/Communication/Protocol.hpp b/Software/VNA_embedded/Application/Communication/Protocol.hpp
index f30449b..6d62027 100644
--- a/Software/VNA_embedded/Application/Communication/Protocol.hpp
+++ b/Software/VNA_embedded/Application/Communication/Protocol.hpp
@@ -101,6 +101,7 @@ enum class PacketType : uint8_t {
     Ack = 7,
 	ClearFlash = 8,
 	PerformFirmwareUpdate = 9,
+	Nack = 10,
 };
 
 using PacketInfo = struct _packetinfo {
diff --git a/Software/VNA_embedded/Application/Drivers/Exti.cpp b/Software/VNA_embedded/Application/Drivers/Exti.cpp
index 5f57e90..204713f 100644
--- a/Software/VNA_embedded/Application/Drivers/Exti.cpp
+++ b/Software/VNA_embedded/Application/Drivers/Exti.cpp
@@ -11,13 +11,13 @@ static constexpr uint8_t MaxEntries = 16;
 static Entry entries[MaxEntries];
 
 void Exti::Init() {
-	HAL_NVIC_SetPriority(EXTI0_IRQn, 1, 0);
-	HAL_NVIC_SetPriority(EXTI1_IRQn, 1, 0);
-	HAL_NVIC_SetPriority(EXTI2_IRQn, 1, 0);
-	HAL_NVIC_SetPriority(EXTI3_IRQn, 1, 0);
-	HAL_NVIC_SetPriority(EXTI4_IRQn, 1, 0);
-	HAL_NVIC_SetPriority(EXTI9_5_IRQn, 1, 0);
-	HAL_NVIC_SetPriority(EXTI15_10_IRQn, 1, 0);
+	HAL_NVIC_SetPriority(EXTI0_IRQn, 5, 0);
+	HAL_NVIC_SetPriority(EXTI1_IRQn, 5, 0);
+	HAL_NVIC_SetPriority(EXTI2_IRQn, 5, 0);
+	HAL_NVIC_SetPriority(EXTI3_IRQn, 5, 0);
+	HAL_NVIC_SetPriority(EXTI4_IRQn, 5, 0);
+	HAL_NVIC_SetPriority(EXTI9_5_IRQn, 5, 0);
+	HAL_NVIC_SetPriority(EXTI15_10_IRQn, 5, 0);
 	HAL_NVIC_EnableIRQ(EXTI0_IRQn);
 	HAL_NVIC_EnableIRQ(EXTI1_IRQn);
 	HAL_NVIC_EnableIRQ(EXTI2_IRQn);
diff --git a/Software/VNA_embedded/Application/Drivers/FPGA.cpp b/Software/VNA_embedded/Application/Drivers/FPGA/FPGA.cpp
similarity index 88%
rename from Software/VNA_embedded/Application/Drivers/FPGA.cpp
rename to Software/VNA_embedded/Application/Drivers/FPGA/FPGA.cpp
index 14d6179..4ee7ef8 100644
--- a/Software/VNA_embedded/Application/Drivers/FPGA.cpp
+++ b/Software/VNA_embedded/Application/Drivers/FPGA/FPGA.cpp
@@ -2,42 +2,18 @@
 #include "delay.hpp"
 #include "stm.hpp"
 #include "main.h"
+#include "FPGA_HAL.hpp"
 
 #define LOG_LEVEL	LOG_LEVEL_DEBUG
 #define LOG_MODULE	"FPGA"
 #include "Log.h"
 
-#define FPGA_SPI			hspi1
-#define CONFIGURATION_SPI	hspi2
-extern SPI_HandleTypeDef FPGA_SPI, CONFIGURATION_SPI;
-
-using GPIO = struct {
-	GPIO_TypeDef *gpio;
-	uint16_t pin;
-};
-static constexpr GPIO CS = {.gpio = FPGA_CS_GPIO_Port, .pin = FPGA_CS_Pin};
-static constexpr GPIO PROGRAM_B = {.gpio = FPGA_PROGRAM_B_GPIO_Port, .pin = FPGA_PROGRAM_B_Pin};
-static constexpr GPIO INIT_B = {.gpio = FPGA_INIT_B_GPIO_Port, .pin = FPGA_INIT_B_Pin};
-static constexpr GPIO DONE = {.gpio = FPGA_DONE_GPIO_Port, .pin = FPGA_DONE_Pin};
-static constexpr GPIO FPGA_RESET = {.gpio = FPGA_RESET_GPIO_Port, .pin = FPGA_RESET_Pin};
-static constexpr GPIO AUX1 = {.gpio = FPGA_AUX1_GPIO_Port, .pin = FPGA_AUX1_Pin};
-static constexpr GPIO AUX2 = {.gpio = FPGA_AUX2_GPIO_Port, .pin = FPGA_AUX2_Pin};
-static constexpr GPIO AUX3 = {.gpio = FPGA_AUX3_GPIO_Port, .pin = FPGA_AUX3_Pin};
-
-static inline void Low(GPIO g) {
-	g.gpio->BSRR = g.pin << 16;
-}
-static inline void High(GPIO g) {
-	g.gpio->BSRR = g.pin;
-}
-bool isHigh(GPIO g) {
-	return g.gpio->IDR & g.pin;
-}
-
 static FPGA::HaltedCallback halted_cb;
 static uint16_t SysCtrlReg = 0x0000;
 static uint16_t ISRMaskReg = 0x0000;
 
+using namespace FPGAHAL;
+
 void WriteRegister(FPGA::Reg reg, uint16_t value) {
 	uint16_t cmd[2] = {(uint16_t) (0x8000 | (uint16_t) reg), value};
 	Low(CS);
@@ -46,6 +22,12 @@ void WriteRegister(FPGA::Reg reg, uint16_t value) {
 }
 
 bool FPGA::Configure(Flash *f, uint32_t start_address, uint32_t bitstream_size) {
+	if(!PROGRAM_B.gpio) {
+		LOG_WARN("PROGRAM_B not defined, assuming FPGA configures itself in master configuration");
+		// wait too allow enough time for FPGA configuration
+		HAL_Delay(2000);
+		return true;
+	}
 	LOG_INFO("Loading bitstream of size %lu...", bitstream_size);
 	Low(PROGRAM_B);
 	while(isHigh(INIT_B));
diff --git a/Software/VNA_embedded/Application/Drivers/FPGA.hpp b/Software/VNA_embedded/Application/Drivers/FPGA/FPGA.hpp
similarity index 100%
rename from Software/VNA_embedded/Application/Drivers/FPGA.hpp
rename to Software/VNA_embedded/Application/Drivers/FPGA/FPGA.hpp
diff --git a/Software/VNA_embedded/Application/Drivers/FPGA/FPGA_HAL.hpp b/Software/VNA_embedded/Application/Drivers/FPGA/FPGA_HAL.hpp
new file mode 100644
index 0000000..87196a1
--- /dev/null
+++ b/Software/VNA_embedded/Application/Drivers/FPGA/FPGA_HAL.hpp
@@ -0,0 +1,43 @@
+#pragma once
+
+#include "stm.hpp"
+#include "main.h"
+
+#define FPGA_SPI			hspi1
+#define CONFIGURATION_SPI	hspi2
+extern SPI_HandleTypeDef FPGA_SPI, CONFIGURATION_SPI;
+
+namespace FPGAHAL {
+
+using GPIO = struct {
+	GPIO_TypeDef *gpio;
+	uint16_t pin;
+};
+static constexpr GPIO CS = {.gpio = FPGA_CS_GPIO_Port, .pin = FPGA_CS_Pin};
+static constexpr GPIO PROGRAM_B = {.gpio = FPGA_PROGRAM_B_GPIO_Port, .pin = FPGA_PROGRAM_B_Pin};
+static constexpr GPIO INIT_B = {.gpio = FPGA_INIT_B_GPIO_Port, .pin = FPGA_INIT_B_Pin};
+static constexpr GPIO DONE = {.gpio = FPGA_DONE_GPIO_Port, .pin = FPGA_DONE_Pin};
+static constexpr GPIO FPGA_RESET = {.gpio = FPGA_RESET_GPIO_Port, .pin = FPGA_RESET_Pin};
+static constexpr GPIO AUX1 = {.gpio = FPGA_AUX1_GPIO_Port, .pin = FPGA_AUX1_Pin};
+static constexpr GPIO AUX2 = {.gpio = FPGA_AUX2_GPIO_Port, .pin = FPGA_AUX2_Pin};
+static constexpr GPIO AUX3 = {.gpio = FPGA_AUX3_GPIO_Port, .pin = FPGA_AUX3_Pin};
+
+static inline void Low(GPIO g) {
+	if(g.gpio) {
+		g.gpio->BSRR = g.pin << 16;
+	}
+}
+static inline void High(GPIO g) {
+	if(g.gpio) {
+		g.gpio->BSRR = g.pin;
+	}
+}
+bool isHigh(GPIO g) {
+	if(g.gpio) {
+		return g.gpio->IDR & g.pin;
+	} else {
+		return false;
+	}
+}
+
+}
diff --git a/Software/VNA_embedded/Application/VNA.cpp b/Software/VNA_embedded/Application/VNA.cpp
index 02edfee..2ebda5f 100644
--- a/Software/VNA_embedded/Application/VNA.cpp
+++ b/Software/VNA_embedded/Application/VNA.cpp
@@ -3,21 +3,15 @@
 #include "max2871.hpp"
 #include "main.h"
 #include "delay.hpp"
-#include "FPGA.hpp"
+#include "FPGA/FPGA.hpp"
 #include <complex>
 #include "Exti.hpp"
+#include "VNA_HAL.hpp"
 
 #define LOG_LEVEL	LOG_LEVEL_INFO
 #define LOG_MODULE	"VNA"
 #include "Log.h"
 
-extern I2C_HandleTypeDef hi2c2;
-extern SPI_HandleTypeDef hspi1;
-
-static Si5351C Si5351 = Si5351C(&hi2c2, 26000000);
-static MAX2871 Source = MAX2871(&hspi1, FPGA_CS_GPIO_Port, FPGA_CS_Pin, nullptr, 0, nullptr, 0, nullptr, 0, GPIOB, GPIO_PIN_4);
-static MAX2871 LO1 = MAX2871(&hspi1, FPGA_CS_GPIO_Port, FPGA_CS_Pin, nullptr, 0, nullptr, 0, nullptr, 0, GPIOB, GPIO_PIN_4);
-
 static constexpr uint32_t IF1 = 60100000;
 static constexpr uint32_t IF1_alternate = 57000000;
 static constexpr uint32_t IF2 = 250000;
@@ -42,6 +36,8 @@ static uint16_t IFTableIndexCnt = 0;
 
 static constexpr uint32_t BandSwitchFrequency = 25000000;
 
+using namespace VNAHAL;
+
 static void HaltedCallback() {
 	LOG_DEBUG("Halted before point %d", pointCnt);
 	// Check if IF table has entry at this point
@@ -59,16 +55,16 @@ static void HaltedCallback() {
 					/ (settings.points - 1);
 	if (frequency < BandSwitchFrequency) {
 		// need the Si5351 as Source
-		Si5351.SetCLK(0, frequency, Si5351C::PLL::B,
+		Si5351.SetCLK(SiChannel::LowbandSource, frequency, Si5351C::PLL::B,
 				Si5351C::DriveStrength::mA2);
 		if (pointCnt == 0) {
 			// First point in sweep, enable CLK
-			Si5351.Enable(0);
+			Si5351.Enable(SiChannel::LowbandSource);
 			FPGA::Disable(FPGA::Periphery::SourceRF);
 		}
 	} else {
 		// first sweep point in highband is also halted, disable lowband source
-		Si5351.Disable(0);
+		Si5351.Disable(SiChannel::LowbandSource);
 		FPGA::Enable(FPGA::Periphery::SourceRF);
 	}
 
@@ -122,8 +118,6 @@ static void FPGA_Interrupt(void*) {
 bool VNA::Init() {
 	LOG_DEBUG("Initializing...");
 
-	// Wait for FPGA to finish configuration
-	Delay::ms(2000);
 	manualMode = false;
 
 	Si5351.Init();
@@ -136,24 +130,25 @@ bool VNA::Init() {
 	while(!Si5351.Locked(Si5351C::PLL::B));
 
 	// Both MAX2871 get a 100MHz reference
-	Si5351.SetCLK(2, 100000000, Si5351C::PLL::A, Si5351C::DriveStrength::mA2);
-	Si5351.Enable(2);
-	Si5351.SetCLK(3, 100000000, Si5351C::PLL::A, Si5351C::DriveStrength::mA2);
-	Si5351.Enable(3);
+	Si5351.SetCLK(SiChannel::Source, 100000000, Si5351C::PLL::A, Si5351C::DriveStrength::mA2);
+	Si5351.Enable(SiChannel::Source);
+	Si5351.SetCLK(SiChannel::LO1, 100000000, Si5351C::PLL::A, Si5351C::DriveStrength::mA2);
+	Si5351.Enable(SiChannel::LO1);
 	// 16MHz FPGA clock
-	Si5351.SetCLK(7, 16000000, Si5351C::PLL::A, Si5351C::DriveStrength::mA2);
-	Si5351.Enable(7);
-	// 10 MHz external reference clock
-	Si5351.SetCLK(6, 10000000, Si5351C::PLL::A, Si5351C::DriveStrength::mA8);
-	Si5351.Enable(6);
+	Si5351.SetCLK(SiChannel::FPGA, 16000000, Si5351C::PLL::A, Si5351C::DriveStrength::mA2);
+	Si5351.Enable(SiChannel::FPGA);
+	// TODO reference settings controllable through USB
+//	// 10 MHz external reference clock
+//	Si5351.SetCLK(6, 10000000, Si5351C::PLL::A, Si5351C::DriveStrength::mA8);
+//	Si5351.Enable(6);
 
 	// Generate second LO with Si5351
-	Si5351.SetCLK(1, IF1 - IF2, Si5351C::PLL::B, Si5351C::DriveStrength::mA2);
-	Si5351.Enable(1);
-	Si5351.SetCLK(4, IF1 - IF2, Si5351C::PLL::B, Si5351C::DriveStrength::mA2);
-	Si5351.Enable(4);
-	Si5351.SetCLK(5, IF1 - IF2, Si5351C::PLL::B, Si5351C::DriveStrength::mA2);
-	Si5351.Enable(5);
+	Si5351.SetCLK(SiChannel::Port1LO2, IF1 - IF2, Si5351C::PLL::B, Si5351C::DriveStrength::mA2);
+	Si5351.Enable(SiChannel::Port1LO2);
+	Si5351.SetCLK(SiChannel::Port2LO2, IF1 - IF2, Si5351C::PLL::B, Si5351C::DriveStrength::mA2);
+	Si5351.Enable(SiChannel::Port2LO2);
+	Si5351.SetCLK(SiChannel::RefLO2, IF1 - IF2, Si5351C::PLL::B, Si5351C::DriveStrength::mA2);
+	Si5351.Enable(SiChannel::RefLO2);
 
 	// PLL reset appears to realign phases of clock signals
 	Si5351.ResetPLL(Si5351C::PLL::B);
@@ -301,7 +296,7 @@ bool VNA::ConfigureSweep(Protocol::SweepSettings s, SweepCallback cb) {
 			IFTable[IFTableIndexCnt].IF1 = used_IF;
 			// Configure LO2 for the changed IF1. This is not necessary right now but it will generate
 			// the correct clock settings
-			Si5351.SetCLK(1, used_IF + IF2, Si5351C::PLL::A, Si5351C::DriveStrength::mA2);
+			Si5351.SetCLK(SiChannel::RefLO2, used_IF + IF2, Si5351C::PLL::A, Si5351C::DriveStrength::mA2);
 			// store calculated clock configuration for later change
 			Si5351.ReadRawCLKConfig(1, IFTable[IFTableIndexCnt].clkconfig);
 			IFTableIndexCnt++;
@@ -349,11 +344,11 @@ bool VNA::ConfigureManual(Protocol::ManualControl m, StatusCallback cb) {
 	FPGA::AbortSweep();
 	// Configure lowband source
 	if (m.SourceLowEN) {
-		Si5351.SetCLK(0, m.SourceLowFrequency, Si5351C::PLL::B,
+		Si5351.SetCLK(SiChannel::LowbandSource, m.SourceLowFrequency, Si5351C::PLL::B,
 				(Si5351C::DriveStrength) m.SourceLowPower);
-		Si5351.Enable(0);
+		Si5351.Enable(SiChannel::LowbandSource);
 	} else {
-		Si5351.Disable(0);
+		Si5351.Disable(SiChannel::LowbandSource);
 	}
 	// Configure highband source
 	Source.SetFrequency(m.SourceHighFrequency);
@@ -365,19 +360,19 @@ bool VNA::ConfigureManual(Protocol::ManualControl m, StatusCallback cb) {
 	// Configure LO2
 	if(m.LO2EN) {
 		// Generate second LO with Si5351
-		Si5351.SetCLK(1, m.LO2Frequency, Si5351C::PLL::B, Si5351C::DriveStrength::mA2);
-		Si5351.Enable(1);
-		Si5351.SetCLK(4, m.LO2Frequency, Si5351C::PLL::B, Si5351C::DriveStrength::mA2);
-		Si5351.Enable(4);
-		Si5351.SetCLK(5, m.LO2Frequency, Si5351C::PLL::B, Si5351C::DriveStrength::mA2);
-		Si5351.Enable(5);
+		Si5351.SetCLK(SiChannel::Port1LO2, m.LO2Frequency, Si5351C::PLL::B, Si5351C::DriveStrength::mA2);
+		Si5351.Enable(SiChannel::Port1LO2);
+		Si5351.SetCLK(SiChannel::Port2LO2, m.LO2Frequency, Si5351C::PLL::B, Si5351C::DriveStrength::mA2);
+		Si5351.Enable(SiChannel::Port2LO2);
+		Si5351.SetCLK(SiChannel::RefLO2, m.LO2Frequency, Si5351C::PLL::B, Si5351C::DriveStrength::mA2);
+		Si5351.Enable(SiChannel::RefLO2);
 
 		// PLL reset appears to realign phases of clock signals
 		Si5351.ResetPLL(Si5351C::PLL::B);
 	} else {
-		Si5351.Disable(1);
-		Si5351.Disable(4);
-		Si5351.Disable(5);
+		Si5351.Disable(SiChannel::Port1LO2);
+		Si5351.Disable(SiChannel::Port2LO2);
+		Si5351.Disable(SiChannel::RefLO2);
 	}
 
 	FPGA::WriteMAX2871Default(Source.GetRegisters());
diff --git a/Software/VNA_embedded/Application/VNA.hpp b/Software/VNA_embedded/Application/VNA.hpp
index 6b65e95..74d379f 100644
--- a/Software/VNA_embedded/Application/VNA.hpp
+++ b/Software/VNA_embedded/Application/VNA.hpp
@@ -2,7 +2,7 @@
 
 #include <cstdint>
 #include "Protocol.hpp"
-#include "FPGA.hpp"
+#include "FPGA/FPGA.hpp"
 
 namespace VNA {
 
diff --git a/Software/VNA_embedded/Application/VNA_HAL.hpp b/Software/VNA_embedded/Application/VNA_HAL.hpp
new file mode 100644
index 0000000..6e3d0fa
--- /dev/null
+++ b/Software/VNA_embedded/Application/VNA_HAL.hpp
@@ -0,0 +1,31 @@
+#pragma once
+
+#include "stm.hpp"
+#include "Si5351C.hpp"
+#include "max2871.hpp"
+#include "main.h"
+
+extern I2C_HandleTypeDef hi2c2;
+extern SPI_HandleTypeDef hspi1;
+
+namespace VNAHAL {
+
+static Si5351C Si5351 = Si5351C(&hi2c2, 26000000);
+static MAX2871 Source = MAX2871(&hspi1, FPGA_CS_GPIO_Port, FPGA_CS_Pin, nullptr, 0, nullptr, 0, nullptr, 0, GPIOB, GPIO_PIN_4);
+static MAX2871 LO1 = MAX2871(&hspi1, FPGA_CS_GPIO_Port, FPGA_CS_Pin, nullptr, 0, nullptr, 0, nullptr, 0, GPIOB, GPIO_PIN_4);
+
+// Mapping of the Si5351 channels to PLLs/Mixers
+namespace SiChannel {
+	enum {
+		Source = 3,
+		LO1 = 5,
+		Port2LO2 = 4,
+		RefLO2 = 1,
+		Port1LO2 = 2,
+		LowbandSource = 1,
+		ReferenceOut = 6,
+		FPGA = 7,
+	};
+}
+
+}