diff --git a/Core/Inc/CAN_Communication.h b/Core/Inc/CAN_Communication.h
index 67102d3..b94c3c6 100644
--- a/Core/Inc/CAN_Communication.h
+++ b/Core/Inc/CAN_Communication.h
@@ -22,6 +22,7 @@
 #define SLAVE_CMD_BASE_ADDRESS 0x500  //
 #define SLAVE_EMERGENCY_ADDRESS 0x001 // Emergency Frame
 #define CLOCK_SYNC_ADDRESS 0x002
+#define MASTER_HEARTBEAT_ADDRESS 0x010
 
 typedef struct {
   int16_t FrameID;
diff --git a/Core/Inc/Clock_Sync.h b/Core/Inc/Clock_Sync.h
index ba00769..b4213c6 100644
--- a/Core/Inc/Clock_Sync.h
+++ b/Core/Inc/Clock_Sync.h
@@ -1,11 +1,34 @@
 #ifndef INC_CLOCK_SYNC_H_
 #define INC_CLOCK_SYNC_H_
 
+/**
+ * @file Clock_Sync.h
+ * @author Jasper v. Blanckenburg (j.blanckenburg@fasttube.de)
+ * @brief Clock synchronization mechanism -- master side
+ * @version 0.1
+ * @date 2022-08-01
+ *
+ * @copyright Copyright (c) 2022
+ *
+ * The slaves' clocks are fairly inaccurate -- too inaccurate for reliable CAN
+ * communication. In order to synchronize the clock frequencies, the slaves need
+ * an external clock source. Since the HSE doesn't work on all slaves, we use
+ * the master as the external clock source. For more detail, take a look at the
+ * clock sync section in the slave code.
+ *
+ * This file handles the master part of the clock sync mechanism: It sends
+ * CLOCK_SYNC frames every 1000 ms and MASTER_HEARTBEAT frames every 100 ms. In
+ * order to keep the time between packets accurate, they are sent from timer
+ * interrupts.
+ */
+
 #include "stm32g4xx_hal.h"
 #include "stm32g4xx_hal_fdcan.h"
+#include "stm32g4xx_hal_tim.h"
 
-void clock_sync_init(FDCAN_HandleTypeDef* can, TIM_HandleTypeDef* timer);
+void clock_sync_init(FDCAN_HandleTypeDef* can, TIM_HandleTypeDef* sync_timer,
+                     TIM_HandleTypeDef* heartbeat_timer);
 
-void clock_sync_handle_timer_complete();
+void clock_sync_handle_timer_complete(TIM_HandleTypeDef* timer);
 
 #endif // INC_CLOCK_SYNC_H_
diff --git a/Core/Src/Clock_Sync.c b/Core/Src/Clock_Sync.c
index ceabb9f..54d94c0 100644
--- a/Core/Src/Clock_Sync.c
+++ b/Core/Src/Clock_Sync.c
@@ -2,19 +2,31 @@
 
 #include "CAN_Communication.h"
 
+#include "stm32g4xx_hal.h"
 #include "stm32g4xx_hal_fdcan.h"
 #include "stm32g4xx_hal_tim.h"
 
 static FDCAN_HandleTypeDef* can;
-static TIM_HandleTypeDef* timer;
+static TIM_HandleTypeDef* sync_timer;
+static TIM_HandleTypeDef* heartbeat_timer;
 
 void clock_sync_init(FDCAN_HandleTypeDef* can_handle,
-                     TIM_HandleTypeDef* timer_handle) {
+                     TIM_HandleTypeDef* sync_timer_handle,
+                     TIM_HandleTypeDef* heartbeat_timer_handle) {
   can = can_handle;
-  timer = timer_handle;
-  HAL_TIM_Base_Start_IT(timer);
+  sync_timer = sync_timer_handle;
+  heartbeat_timer = heartbeat_timer_handle;
+  HAL_TIM_Base_Start_IT(heartbeat_timer);
+  // Delay between starting the timers so the interrupts don't fire at the same
+  // time
+  HAL_Delay(50);
+  HAL_TIM_Base_Start_IT(sync_timer);
 }
 
-void clock_sync_handle_timer_complete() {
-  CAN_Transmit(can, CLOCK_SYNC_ADDRESS, NULL, 0);
+void clock_sync_handle_timer_complete(TIM_HandleTypeDef* timer) {
+  if (timer == sync_timer) {
+    CAN_Transmit(can, CLOCK_SYNC_ADDRESS, NULL, 0);
+  } else if (timer == heartbeat_timer) {
+    CAN_Transmit(can, MASTER_HEARTBEAT_ADDRESS, NULL, 0);
+  }
 }
diff --git a/Core/Src/main.c b/Core/Src/main.c
index aa91e83..2246e64 100644
--- a/Core/Src/main.c
+++ b/Core/Src/main.c
@@ -56,6 +56,7 @@ FDCAN_HandleTypeDef hfdcan1;
 SPI_HandleTypeDef hspi1;
 
 TIM_HandleTypeDef htim1;
+TIM_HandleTypeDef htim8;
 
 /* USER CODE BEGIN PV */
 
@@ -68,6 +69,7 @@ static void MX_FDCAN1_Init(void);
 static void MX_SPI1_Init(void);
 static void MX_CRC_Init(void);
 static void MX_TIM1_Init(void);
+static void MX_TIM8_Init(void);
 /* USER CODE BEGIN PFP */
 void setAMSError(void);
 /* USER CODE END PFP */
@@ -75,8 +77,8 @@ void setAMSError(void);
 /* Private user code ---------------------------------------------------------*/
 /* USER CODE BEGIN 0 */
 void HAL_TIM_PeriodElapsedCallback(TIM_HandleTypeDef* htim) {
-  if (htim == &htim1) {
-    clock_sync_handle_timer_complete();
+  if (htim == &htim1 || htim == &htim8) {
+    clock_sync_handle_timer_complete(htim);
   }
 }
 
@@ -117,13 +119,14 @@ int main(void) {
   MX_SPI1_Init();
   MX_CRC_Init();
   MX_TIM1_Init();
+  MX_TIM8_Init();
   /* USER CODE BEGIN 2 */
 
   airstates = init_AIR_State_Maschine();
   set_SPI_errorInfo(&defaulterrorhandle);
   spi_communication_init(&hspi1, &airstates);
   CAN_Init(&hfdcan1);
-  clock_sync_init(&hfdcan1, &htim1);
+  clock_sync_init(&hfdcan1, &htim1, &htim8);
   initSlaves();
 
   HAL_GPIO_WritePin(Status_LED_GPIO_Port, Status_LED_Pin, GPIO_PIN_SET);
@@ -340,6 +343,48 @@ static void MX_TIM1_Init(void) {
   /* USER CODE END TIM1_Init 2 */
 }
 
+/**
+ * @brief TIM8 Initialization Function
+ * @param None
+ * @retval None
+ */
+static void MX_TIM8_Init(void) {
+
+  /* USER CODE BEGIN TIM8_Init 0 */
+
+  /* USER CODE END TIM8_Init 0 */
+
+  TIM_ClockConfigTypeDef sClockSourceConfig = {0};
+  TIM_MasterConfigTypeDef sMasterConfig = {0};
+
+  /* USER CODE BEGIN TIM8_Init 1 */
+
+  /* USER CODE END TIM8_Init 1 */
+  htim8.Instance = TIM8;
+  htim8.Init.Prescaler = 1599;
+  htim8.Init.CounterMode = TIM_COUNTERMODE_UP;
+  htim8.Init.Period = 999;
+  htim8.Init.ClockDivision = TIM_CLOCKDIVISION_DIV1;
+  htim8.Init.RepetitionCounter = 0;
+  htim8.Init.AutoReloadPreload = TIM_AUTORELOAD_PRELOAD_DISABLE;
+  if (HAL_TIM_Base_Init(&htim8) != HAL_OK) {
+    Error_Handler();
+  }
+  sClockSourceConfig.ClockSource = TIM_CLOCKSOURCE_INTERNAL;
+  if (HAL_TIM_ConfigClockSource(&htim8, &sClockSourceConfig) != HAL_OK) {
+    Error_Handler();
+  }
+  sMasterConfig.MasterOutputTrigger = TIM_TRGO_RESET;
+  sMasterConfig.MasterOutputTrigger2 = TIM_TRGO2_RESET;
+  sMasterConfig.MasterSlaveMode = TIM_MASTERSLAVEMODE_DISABLE;
+  if (HAL_TIMEx_MasterConfigSynchronization(&htim8, &sMasterConfig) != HAL_OK) {
+    Error_Handler();
+  }
+  /* USER CODE BEGIN TIM8_Init 2 */
+
+  /* USER CODE END TIM8_Init 2 */
+}
+
 /**
  * @brief GPIO Initialization Function
  * @param None
diff --git a/Core/Src/stm32g4xx_hal_msp.c b/Core/Src/stm32g4xx_hal_msp.c
index de8a6db..9a5ba16 100644
--- a/Core/Src/stm32g4xx_hal_msp.c
+++ b/Core/Src/stm32g4xx_hal_msp.c
@@ -315,6 +315,17 @@ void HAL_TIM_Base_MspInit(TIM_HandleTypeDef* htim_base)
 
   /* USER CODE END TIM1_MspInit 1 */
   }
+  else if(htim_base->Instance==TIM8)
+  {
+  /* USER CODE BEGIN TIM8_MspInit 0 */
+
+  /* USER CODE END TIM8_MspInit 0 */
+    /* Peripheral clock enable */
+    __HAL_RCC_TIM8_CLK_ENABLE();
+  /* USER CODE BEGIN TIM8_MspInit 1 */
+
+  /* USER CODE END TIM8_MspInit 1 */
+  }
 
 }
 
@@ -340,6 +351,17 @@ void HAL_TIM_Base_MspDeInit(TIM_HandleTypeDef* htim_base)
 
   /* USER CODE END TIM1_MspDeInit 1 */
   }
+  else if(htim_base->Instance==TIM8)
+  {
+  /* USER CODE BEGIN TIM8_MspDeInit 0 */
+
+  /* USER CODE END TIM8_MspDeInit 0 */
+    /* Peripheral clock disable */
+    __HAL_RCC_TIM8_CLK_DISABLE();
+  /* USER CODE BEGIN TIM8_MspDeInit 1 */
+
+  /* USER CODE END TIM8_MspDeInit 1 */
+  }
 
 }
 
diff --git a/Makefile b/Makefile
index adfcffb..8bbcdff 100644
--- a/Makefile
+++ b/Makefile
@@ -1,5 +1,5 @@
 ##########################################################################################################################
-# File automatically-generated by tool: [projectgenerator] version: [3.17.1] date: [Sat Jul 30 22:35:37 CEST 2022] 
+# File automatically-generated by tool: [projectgenerator] version: [3.17.1] date: [Mon Aug 01 08:27:49 CEST 2022] 
 ##########################################################################################################################
 
 # ------------------------------------------------
diff --git a/Master_Control.ioc b/Master_Control.ioc
index c21dfb3..0c742fe 100644
--- a/Master_Control.ioc
+++ b/Master_Control.ioc
@@ -19,7 +19,8 @@ Mcu.IP3=RCC
 Mcu.IP4=SPI1
 Mcu.IP5=SYS
 Mcu.IP6=TIM1
-Mcu.IPNb=7
+Mcu.IP7=TIM8
+Mcu.IPNb=8
 Mcu.Name=STM32G441CBTx
 Mcu.Package=LQFP48
 Mcu.Pin0=PC13
@@ -36,6 +37,7 @@ Mcu.Pin18=VP_SYS_VS_Systick
 Mcu.Pin19=VP_SYS_VS_DBSignals
 Mcu.Pin2=PC15-OSC32_OUT
 Mcu.Pin20=VP_TIM1_VS_ClockSourceINT
+Mcu.Pin21=VP_TIM8_VS_ClockSourceINT
 Mcu.Pin3=PA5
 Mcu.Pin4=PA6
 Mcu.Pin5=PA7
@@ -43,7 +45,7 @@ Mcu.Pin6=PB0
 Mcu.Pin7=PA8
 Mcu.Pin8=PA9
 Mcu.Pin9=PA10
-Mcu.PinsNb=21
+Mcu.PinsNb=22
 Mcu.ThirdPartyNb=0
 Mcu.UserConstants=
 Mcu.UserName=STM32G441CBTx
@@ -149,7 +151,7 @@ ProjectManager.StackSize=0x400
 ProjectManager.TargetToolchain=Makefile
 ProjectManager.ToolChainLocation=
 ProjectManager.UnderRoot=false
-ProjectManager.functionlistsort=1-MX_GPIO_Init-GPIO-false-HAL-true,2-SystemClock_Config-RCC-false-HAL-false,3-MX_FDCAN1_Init-FDCAN1-false-HAL-true,4-MX_SPI1_Init-SPI1-false-HAL-true,5-MX_CRC_Init-CRC-false-HAL-true
+ProjectManager.functionlistsort=1-MX_GPIO_Init-GPIO-false-HAL-true,2-SystemClock_Config-RCC-false-HAL-false,3-MX_FDCAN1_Init-FDCAN1-false-HAL-true,4-MX_SPI1_Init-SPI1-false-HAL-true,5-MX_CRC_Init-CRC-false-HAL-true,6-MX_TIM1_Init-TIM1-false-HAL-true
 RCC.ADC12Freq_Value=16000000
 RCC.AHBFreq_Value=16000000
 RCC.APB1Freq_Value=16000000
@@ -204,6 +206,9 @@ TIM1.CounterMode=TIM_COUNTERMODE_UP
 TIM1.IPParameters=Prescaler,CounterMode,PeriodNoDither
 TIM1.PeriodNoDither=9999
 TIM1.Prescaler=1599
+TIM8.IPParameters=Prescaler,PeriodNoDither
+TIM8.PeriodNoDither=999
+TIM8.Prescaler=1599
 VP_CRC_VS_CRC.Mode=CRC_Activate
 VP_CRC_VS_CRC.Signal=CRC_VS_CRC
 VP_SYS_VS_DBSignals.Mode=DisableDeadBatterySignals
@@ -212,4 +217,6 @@ VP_SYS_VS_Systick.Mode=SysTick
 VP_SYS_VS_Systick.Signal=SYS_VS_Systick
 VP_TIM1_VS_ClockSourceINT.Mode=Internal
 VP_TIM1_VS_ClockSourceINT.Signal=TIM1_VS_ClockSourceINT
+VP_TIM8_VS_ClockSourceINT.Mode=Internal
+VP_TIM8_VS_ClockSourceINT.Signal=TIM8_VS_ClockSourceINT
 board=custom