diff --git a/init.c b/init.c
index 52c35ac..26e765f 100644
--- a/init.c
+++ b/init.c
@@ -61,7 +61,10 @@ void init_usart(void)
 
 void init_systick(void)
 {
-	SysTick_CSR = (SysTick_CSR & ~SysTick_CSR_CLKSOURCE) | SysTick_CSR_CLKSOURCE_CORE;
+	//SysTick_CSR = (SysTick_CSR & ~SysTick_CSR_CLKSOURCE) | (1 << __CTZ(SysTick_CSR_CLKSOURCE));
+
+	patch_register(SysTick_CSR, SysTick_CSR_CLKSOURCE, 1); // 1 - core, 0 - div 8
+
 	SysTick_RELOAD = 16000; // 1ms interrupt @ 16MHz core clock
 	SysTick_CSR |= SysTick_CSR_TICKINT | SysTick_CSR_ENABLE;
 }
@@ -103,6 +106,8 @@ void init_dac(void)
 	gpio_set_mode(GPIOA, BIT4, MODER_ANALOG); // PA4 - DAC CH1 out
 
 	DAC_CR |= DAC_CR_EN1; // enable first channel
+
+	DAC_DHR12R1 = 0; // reset value
 }
 
 
@@ -114,14 +119,14 @@ void init_pwm1(void)
 	// using timer 3, channel 1
 	gpio_set_af(GPIOA, BIT6, AF2);
 
-	patch_register(&TIM3_CCMR1, TIM_CCMR1_OC1M, TIM_OCM_PWM1); // set PWM1 mode
+	patch_register(TIM3_CCMR1, TIM_CCMR1_OC1M, TIM_OCM_PWM1); // set PWM1 mode
 
 	TIM3_CCMR1 |= TIM_CCMR1_OC1PE; // preload enable
 	TIM3_CR1 |= TIM_CR1_ARPE; // auto reload is buffered
 	TIM3_CCER |= TIM_CCER_CC1E; // enable output compare (PWM output)
 
-	patch_register(&TIM3_CR1, TIM_CR1_CMS, TIM_CMS_EDGE); // centering mode
-	patch_register(&TIM3_CR1, TIM_CR1_DIR, 0); // count upwards only
+	patch_register(TIM3_CR1, TIM_CR1_CMS, TIM_CMS_EDGE); // centering mode
+	patch_register(TIM3_CR1, TIM_CR1_DIR, 0); // count upwards only
 
 	// frequency set to 16 kHz
 
diff --git a/lib/common.c b/lib/common.c
index 0dd7ad0..a5a42c6 100644
--- a/lib/common.c
+++ b/lib/common.c
@@ -10,9 +10,12 @@ inline uint32_t __RBIT(uint32_t value)
 }
 
 
+// implemented as a macro for more efficient code
+
+/*
 __attribute__((always_inline))
 inline void patch_register(io32_t reg, uint32_t mask, uint32_t replacement)
 {
-	*reg &= ~mask;
-	*reg |= replacement << __CTZ(mask);
+	*reg = (*reg & ~mask) | (replacement << __CTZ(mask));
 }
+*/
diff --git a/lib/common.h b/lib/common.h
index d157e6a..1bf1f33 100644
--- a/lib/common.h
+++ b/lib/common.h
@@ -87,8 +87,15 @@ uint32_t __RBIT(uint32_t value); // defined in c file as inline asm
 #define BIT31 BIT(31)
 
 
-void patch_register(io32_t reg, uint32_t mask, uint32_t replacement);
 
+// reg - MMIO32
+// mask - uint32_t
+// replacement - uint32_t (value that goes in place of mask, right-aligned)
+//
+// example: original value 0x12345678, patch_register(reg, 0xF00, 0xC) -> 0x12345C78
+#define patch_register(reg, mask, replacement) (reg) = ((reg) & ~(mask)) | ((replacement) << __CTZ(mask))
+
+//void patch_register(io32_t reg, uint32_t mask, uint32_t replacement);
 
 
 #include "defs_base.h"
diff --git a/main.c b/main.c
index c020ac6..6cd7387 100644
--- a/main.c
+++ b/main.c
@@ -15,6 +15,8 @@
 static bool gate_closed = false;
 static uint32_t gate_cnt = 0;
 
+float exposure_out, exposure_accum;
+uint32_t exposure_cnt;
 
 /** IRQ */
 void USART2_IRQHandler(void)
@@ -99,15 +101,31 @@ int main(void)
 	char buf[200];
 
 	usart_tx_string(USART2, "DAQ system started.\n");
+	delay_ms(100);
 
+	bool first = true;
 	while (1) {
-		delay_ms(200);
-
 		float cels = measure_temp();
 		float angle = measure_angle();
 		float resis = measure_resistance();
 		float expos = measure_exposure();
 
+		// --- exposure averaging
+		exposure_accum += expos;
+		exposure_cnt++;
+
+		if (exposure_cnt >= 5) {
+			exposure_out = exposure_accum / exposure_cnt;
+			exposure_accum = 0;
+			exposure_cnt = 0;
+		}
+
+		if (first) {
+			exposure_out = expos; // pretend it's averaged
+		}
+		// ---
+
+
 		buf_reset(buf);
 		buf_append_str(buf, "T ");
 		buf_append_flt(buf, cels, 1);
@@ -122,7 +140,7 @@ int main(void)
 		buf_append_str(buf, " | ");
 
 		buf_append_str(buf, "L ");
-		buf_append_flt(buf, expos, 1);
+		buf_append_flt(buf, exposure_out, 1);
 		buf_append_str(buf, "% | ");
 
 		buf_append_str(buf, "G ");
@@ -141,5 +159,8 @@ int main(void)
 		buf_append_str(buf, "\n");
 
 		usart_tx_string(USART2, buf);
+
+		delay_ms(100);
+		first = false;
 	}
 }