diff --git a/audio.c b/audio.c
index f083906..735fae9 100644
--- a/audio.c
+++ b/audio.c
@@ -275,12 +275,12 @@ void AUDIO_PlayBeep(beep_type_t Beep)
 				GPIO_ClearBit(&GPIOA->DATA, GPIOA_PIN_VOICE_1);
 			else
 				GPIO_SetBit(&GPIOA->DATA, GPIOA_PIN_VOICE_1);
-			SYSTICK_DelayUs(1000);
+			SYSTICK_Delay250us(4000);
 			GPIO_SetBit(&GPIOA->DATA, GPIOA_PIN_VOICE_0);
-			SYSTICK_DelayUs(1200);
+			SYSTICK_Delay250us(4800);
 			GPIO_ClearBit(&GPIOA->DATA, GPIOA_PIN_VOICE_0);
 			VoiceID <<= 1;
-			SYSTICK_DelayUs(200);
+			SYSTICK_Delay250us(800);
 		}
 	}
 
diff --git a/driver/bk4819.c b/driver/bk4819.c
index 0ef3f2f..08131d7 100644
--- a/driver/bk4819.c
+++ b/driver/bk4819.c
@@ -144,7 +144,7 @@ static uint16_t BK4819_ReadU16(void)
 
 	PORTCON_PORTC_IE = (PORTCON_PORTC_IE & ~PORTCON_PORTC_IE_C2_MASK) | PORTCON_PORTC_IE_C2_BITS_ENABLE;
 	GPIOC->DIR = (GPIOC->DIR & ~GPIO_DIR_2_MASK) | GPIO_DIR_2_BITS_INPUT;
-	SYSTICK_DelayUs(1);
+	SYSTICK_Delay250ns(4);
 
 	Value = 0;
 	for (i = 0; i < 16; i++)
@@ -152,9 +152,9 @@ static uint16_t BK4819_ReadU16(void)
 		Value <<= 1;
 		Value |= GPIO_CheckBit(&GPIOC->DATA, GPIOC_PIN_BK4819_SDA);
 		GPIO_SetBit(&GPIOC->DATA, GPIOC_PIN_BK4819_SCL);
-		SYSTICK_DelayUs(1);
+		SYSTICK_Delay250ns(4);
 		GPIO_ClearBit(&GPIOC->DATA, GPIOC_PIN_BK4819_SCL);
-		SYSTICK_DelayUs(1);
+		SYSTICK_Delay250ns(4);
 	}
 	PORTCON_PORTC_IE = (PORTCON_PORTC_IE & ~PORTCON_PORTC_IE_C2_MASK) | PORTCON_PORTC_IE_C2_BITS_DISABLE;
 	GPIOC->DIR = (GPIOC->DIR & ~GPIO_DIR_2_MASK) | GPIO_DIR_2_BITS_OUTPUT;
@@ -169,14 +169,14 @@ uint16_t BK4819_ReadRegister(const uint8_t Register)
 	GPIO_SetBit(&GPIOC->DATA, GPIOC_PIN_BK4819_SCN);
 	GPIO_ClearBit(&GPIOC->DATA, GPIOC_PIN_BK4819_SCL);
 
-	SYSTICK_DelayUs(1);
+	SYSTICK_Delay250ns(4);
 
 	GPIO_ClearBit(&GPIOC->DATA, GPIOC_PIN_BK4819_SCN);
 	BK4819_WriteU8(Register | 0x80);
 	Value = BK4819_ReadU16();
 	GPIO_SetBit(&GPIOC->DATA, GPIOC_PIN_BK4819_SCN);
 
-	SYSTICK_DelayUs(1);
+	SYSTICK_Delay250ns(4);
 
 	GPIO_SetBit(&GPIOC->DATA, GPIOC_PIN_BK4819_SCL);
 	GPIO_SetBit(&GPIOC->DATA, GPIOC_PIN_BK4819_SDA);
@@ -188,12 +188,12 @@ void BK4819_WriteRegister(const uint8_t Register, uint16_t Data)
 {
 	GPIO_SetBit(&GPIOC->DATA, GPIOC_PIN_BK4819_SCN);
 	GPIO_ClearBit(&GPIOC->DATA, GPIOC_PIN_BK4819_SCL);
-	SYSTICK_DelayUs(1);
+	SYSTICK_Delay250ns(4);
 	GPIO_ClearBit(&GPIOC->DATA, GPIOC_PIN_BK4819_SCN);
 	BK4819_WriteU8(Register);
 	BK4819_WriteU16(Data);
 	GPIO_SetBit(&GPIOC->DATA, GPIOC_PIN_BK4819_SCN);
-	SYSTICK_DelayUs(1);
+	SYSTICK_Delay250ns(4);
 	GPIO_SetBit(&GPIOC->DATA, GPIOC_PIN_BK4819_SCL);
 	GPIO_SetBit(&GPIOC->DATA, GPIOC_PIN_BK4819_SDA);
 }
@@ -210,14 +210,14 @@ void BK4819_WriteU8(uint8_t Data)
 		else
 			GPIO_SetBit(&GPIOC->DATA, GPIOC_PIN_BK4819_SDA);
 
-		SYSTICK_DelayUs(1);
+		SYSTICK_Delay250ns(4);
 		GPIO_SetBit(&GPIOC->DATA, GPIOC_PIN_BK4819_SCL);
-		SYSTICK_DelayUs(1);
+		SYSTICK_Delay250ns(4);
 
 		Data <<= 1;
 
 		GPIO_ClearBit(&GPIOC->DATA, GPIOC_PIN_BK4819_SCL);
-		SYSTICK_DelayUs(1);
+		SYSTICK_Delay250ns(4);
 	}
 }
 
@@ -233,14 +233,14 @@ void BK4819_WriteU16(uint16_t Data)
 		else
 			GPIO_SetBit(&GPIOC->DATA, GPIOC_PIN_BK4819_SDA);
 
-		SYSTICK_DelayUs(1);
+		SYSTICK_Delay250ns(4);
 		GPIO_SetBit(&GPIOC->DATA, GPIOC_PIN_BK4819_SCL);
 
 		Data <<= 1;
 
-		SYSTICK_DelayUs(1);
+		SYSTICK_Delay250ns(4);
 		GPIO_ClearBit(&GPIOC->DATA, GPIOC_PIN_BK4819_SCL);
-		SYSTICK_DelayUs(1);
+		SYSTICK_Delay250ns(4);
 	}
 }
 void BK4819_EnableAFC(void)
diff --git a/driver/i2c.c b/driver/i2c.c
index eb844d2..dda2212 100644
--- a/driver/i2c.c
+++ b/driver/i2c.c
@@ -23,25 +23,25 @@
 void I2C_Start(void)
 {
 	GPIO_SetBit(&GPIOA->DATA, GPIOA_PIN_I2C_SDA);
-	SYSTICK_DelayUs(1);
+	SYSTICK_Delay250ns(4);
 	GPIO_SetBit(&GPIOA->DATA, GPIOA_PIN_I2C_SCL);
-	SYSTICK_DelayUs(1);
+	SYSTICK_Delay250ns(4);
 	GPIO_ClearBit(&GPIOA->DATA, GPIOA_PIN_I2C_SDA);
-	SYSTICK_DelayUs(1);
+	SYSTICK_Delay250ns(4);
 	GPIO_ClearBit(&GPIOA->DATA, GPIOA_PIN_I2C_SCL);
-	SYSTICK_DelayUs(1);
+	SYSTICK_Delay250ns(4);
 }
 
 void I2C_Stop(void)
 {
 	GPIO_ClearBit(&GPIOA->DATA, GPIOA_PIN_I2C_SDA);
-	SYSTICK_DelayUs(1);
+	SYSTICK_Delay250ns(4);
 	GPIO_ClearBit(&GPIOA->DATA, GPIOA_PIN_I2C_SCL);
-	SYSTICK_DelayUs(1);
+	SYSTICK_Delay250ns(4);
 	GPIO_SetBit(&GPIOA->DATA, GPIOA_PIN_I2C_SCL);
-	SYSTICK_DelayUs(1);
+	SYSTICK_Delay250ns(4);
 	GPIO_SetBit(&GPIOA->DATA, GPIOA_PIN_I2C_SDA);
-	SYSTICK_DelayUs(1);
+	SYSTICK_Delay250ns(4);
 }
 
 uint8_t I2C_Read_fast(bool bFinal)
@@ -97,31 +97,31 @@ uint8_t I2C_Read(bool bFinal)
 	for (i = 0; i < 8; i++)
 	{
 		GPIO_ClearBit(&GPIOA->DATA, GPIOA_PIN_I2C_SCL);
-		SYSTICK_DelayUs(1);
+		SYSTICK_Delay250ns(4);
 		GPIO_SetBit(&GPIOA->DATA, GPIOA_PIN_I2C_SCL);
-		SYSTICK_DelayUs(1);
+		SYSTICK_Delay250ns(4);
 		Data <<= 1;
-		SYSTICK_DelayUs(1);
+		SYSTICK_Delay250ns(4);
 		if (GPIO_CheckBit(&GPIOA->DATA, GPIOA_PIN_I2C_SDA))
 			Data |= 1U;
 		GPIO_ClearBit(&GPIOA->DATA, GPIOA_PIN_I2C_SCL);
-		SYSTICK_DelayUs(1);
+		SYSTICK_Delay250ns(4);
 	}
 
 	PORTCON_PORTA_IE &= ~PORTCON_PORTA_IE_A11_MASK;
 	PORTCON_PORTA_OD |= PORTCON_PORTA_OD_A11_BITS_ENABLE;
 	GPIOA->DIR |= GPIO_DIR_11_BITS_OUTPUT;
 	GPIO_ClearBit(&GPIOA->DATA, GPIOA_PIN_I2C_SCL);
-	SYSTICK_DelayUs(1);
+	SYSTICK_Delay250ns(4);
 	if (bFinal)
 		GPIO_SetBit(&GPIOA->DATA, GPIOA_PIN_I2C_SDA);
 	else
 		GPIO_ClearBit(&GPIOA->DATA, GPIOA_PIN_I2C_SDA);
-	SYSTICK_DelayUs(1);
+	SYSTICK_Delay250ns(4);
 	GPIO_SetBit(&GPIOA->DATA, GPIOA_PIN_I2C_SCL);
-	SYSTICK_DelayUs(1);
+	SYSTICK_Delay250ns(4);
 	GPIO_ClearBit(&GPIOA->DATA, GPIOA_PIN_I2C_SCL);
-	SYSTICK_DelayUs(1);
+	SYSTICK_Delay250ns(4);
 
 	return Data;
 }
@@ -132,7 +132,7 @@ int I2C_Write(uint8_t Data)
 	int ret = -1;
 
 	GPIO_ClearBit(&GPIOA->DATA, GPIOA_PIN_I2C_SCL);
-	SYSTICK_DelayUs(1);
+	SYSTICK_Delay250ns(4);
 	for (i = 0; i < 8; i++) {
 		if ((Data & 0x80) == 0) {
 			GPIO_ClearBit(&GPIOA->DATA, GPIOA_PIN_I2C_SDA);
@@ -140,20 +140,20 @@ int I2C_Write(uint8_t Data)
 			GPIO_SetBit(&GPIOA->DATA, GPIOA_PIN_I2C_SDA);
 		}
 		Data <<= 1;
-		SYSTICK_DelayUs(1);
+		SYSTICK_Delay250ns(4);
 		GPIO_SetBit(&GPIOA->DATA, GPIOA_PIN_I2C_SCL);
-		SYSTICK_DelayUs(1);
+		SYSTICK_Delay250ns(4);
 		GPIO_ClearBit(&GPIOA->DATA, GPIOA_PIN_I2C_SCL);
-		SYSTICK_DelayUs(1);
+		SYSTICK_Delay250ns(4);
 	}
 
 	PORTCON_PORTA_IE |= PORTCON_PORTA_IE_A11_BITS_ENABLE;
 	PORTCON_PORTA_OD &= ~PORTCON_PORTA_OD_A11_MASK;
 	GPIOA->DIR &= ~GPIO_DIR_11_MASK;
 	GPIO_SetBit(&GPIOA->DATA, GPIOA_PIN_I2C_SDA);
-	SYSTICK_DelayUs(1);
+	SYSTICK_Delay250ns(4);
 	GPIO_SetBit(&GPIOA->DATA, GPIOA_PIN_I2C_SCL);
-	SYSTICK_DelayUs(1);
+	SYSTICK_Delay250ns(4);
 
 	for (i = 0; i < 255; i++) {
 		if (GPIO_CheckBit(&GPIOA->DATA, GPIOA_PIN_I2C_SDA) == 0) {
@@ -163,7 +163,7 @@ int I2C_Write(uint8_t Data)
 	}
 
 	GPIO_ClearBit(&GPIOA->DATA, GPIOA_PIN_I2C_SCL);
-	SYSTICK_DelayUs(1);
+	SYSTICK_Delay250ns(4);
 	PORTCON_PORTA_IE &= ~PORTCON_PORTA_IE_A11_MASK;
 	PORTCON_PORTA_OD |= PORTCON_PORTA_OD_A11_BITS_ENABLE;
 	GPIOA->DIR |= GPIO_DIR_11_BITS_OUTPUT;
diff --git a/driver/keyboard.c b/driver/keyboard.c
index b50b25f..315f536 100644
--- a/driver/keyboard.c
+++ b/driver/keyboard.c
@@ -125,7 +125,7 @@ key_code_t KEYBOARD_Poll(void)
 		for (i = 0, k = 0, reg = 0; i < 3 && k < 8; i++, k++)
 		{
 			uint16_t reg2;
-			SYSTICK_DelayUs(1);
+			SYSTICK_Delay250ns(4);
 			reg2 = GPIOA->DATA;
 			if (reg != reg2)
 			{	// noise
diff --git a/driver/system.c b/driver/system.c
index abcfb06..22a210f 100644
--- a/driver/system.c
+++ b/driver/system.c
@@ -19,9 +19,9 @@
 #include "driver/system.h"
 #include "driver/systick.h"
 
-void SYSTEM_DelayMs(uint32_t Delay)
+void SYSTEM_DelayMs(const uint32_t Delay)
 {
-	SYSTICK_DelayUs(Delay * 1000);
+	SYSTICK_Delay250ns(Delay * 4000);
 }
 
 void SYSTEM_ConfigureClocks(void)
diff --git a/driver/system.h b/driver/system.h
index 6f285b2..93937f6 100644
--- a/driver/system.h
+++ b/driver/system.h
@@ -19,7 +19,7 @@
 
 #include <stdint.h>
 
-void SYSTEM_DelayMs(uint32_t Delay);
+void SYSTEM_DelayMs(const uint32_t Delay);
 void SYSTEM_ConfigureClocks(void);
 
 #endif
diff --git a/driver/systick.c b/driver/systick.c
index d72eee9..d2aafe0 100644
--- a/driver/systick.c
+++ b/driver/systick.c
@@ -27,27 +27,6 @@ void SYSTICK_Init(void)
 	gTickMultiplier = 48;
 }
 
-void SYSTICK_DelayUs(const uint32_t Delay)
-{
-	const uint32_t ticks = Delay * gTickMultiplier;
-	uint32_t i           = 0;
-	uint32_t Start       = SysTick->LOAD;
-	uint32_t Previous    = SysTick->VAL;
-
-	do {
-		uint32_t Delta;
-		uint32_t Current;
-
-		do Current = SysTick->VAL;
-		while (Current == Previous);
-
-		Delta = (Current < Previous) ? -Current : Start - Current;
-		i += Delta + Previous;
-		Previous = Current;
-
-	} while (i < ticks);
-}
-
 void SYSTICK_Delay250ns(const uint32_t Delay)
 {
 	const uint32_t ticks = (Delay * gTickMultiplier) >> 2;
diff --git a/driver/systick.h b/driver/systick.h
index 9e2871f..9acc6ff 100644
--- a/driver/systick.h
+++ b/driver/systick.h
@@ -20,7 +20,6 @@
 #include <stdint.h>
 
 void SYSTICK_Init(void);
-void SYSTICK_DelayUs(const uint32_t Delay);
 void SYSTICK_Delay250ns(const uint32_t Delay);
 
 #endif
diff --git a/firmware.bin b/firmware.bin
index a96a8fa..8d485c3 100644
Binary files a/firmware.bin and b/firmware.bin differ
diff --git a/firmware.packed.bin b/firmware.packed.bin
index b30f5f6..ec1034f 100644
Binary files a/firmware.packed.bin and b/firmware.packed.bin differ