diff --git a/sys/arch/arm/samsung/exynos4_reg.h b/sys/arch/arm/samsung/exynos4_reg.h
index 325c252bb335..c800d1102816 100644
--- a/sys/arch/arm/samsung/exynos4_reg.h
+++ b/sys/arch/arm/samsung/exynos4_reg.h
@@ -178,7 +178,7 @@
 #define EXYNOS4_MTCADC_ISP_OFFSET		0x02150000	/* (specialised?) AD Converter */
 #define EXYNOS4_PWM_ISP_OFFSET			0x02160000	/* PWM */
 #define EXYNOS4_WDT_ISP_OFFSET			0x02170000	/* Watch Dog Timer */
-#define EXYNOS4_MCUCTL_ISP_OFFSET		0x02180000	/* XXX micro controller control unit? */
+#define EXYNOS4_MCUCTL_ISP_OFFSET		0x02180000	/* power module control unit? */
 #define EXYNOS4_UART_ISP_OFFSET			0x02190000	/* uart base clock */
 #define EXYNOS4_SPI0_ISP_OFFSET			0x021A0000
 #define EXYNOS4_SPI1_ISP_OFFSET			0x021B0000
diff --git a/sys/arch/arm/samsung/exynos5_reg.h b/sys/arch/arm/samsung/exynos5_reg.h
index ec4efb601b8a..e9116e7d633f 100644
--- a/sys/arch/arm/samsung/exynos5_reg.h
+++ b/sys/arch/arm/samsung/exynos5_reg.h
@@ -1,4 +1,4 @@
-/*	$NetBSD: exynos5_reg.h,v 1.4 2014/05/21 13:02:46 reinoud Exp $	*/
+/*	$NetBSD: exynos5_reg.h,v 1.5 2014/06/03 15:51:59 reinoud Exp $	*/
 
 /*-
  * Copyright (c) 2014 The NetBSD Foundation, Inc.
@@ -144,7 +144,7 @@
 #define EXYNOS5_USB2_DEVICE_LINK_OFFSET		0x02140000
 #define EXYNOS5_MIPI_HSI_OFFSET			0x02160000
 #define EXYNOS5_SATA PHY CONTROL_OFFSET		0x02170000
-#define EXYNOS5_MCUCTL_IOP_OFFSET		0x02180000
+#define EXYNOS5_MCUCTL_IOP_OFFSET		0x02180000	/* XXX unknown XXX */
 #define EXYNOS5_WDT_IOP_OFFSET			0x02190000
 #define EXYNOS5_PDMA0				0x021A0000
 #define EXYNOS5_PDMA1				0x021B0000