diff --git a/README.md b/README.md
index 234b8c8..120c41e 100644
--- a/README.md
+++ b/README.md
@@ -1,2 +1,26 @@
 # stm32-ada
 Ada bindings for STM32 internals
+
+## Hardware quirks and workarounds
+
+### APB
+
+APB does not support writes of parts of 32-bit registers.
+The library provides acess to register fields as records.
+This could lead compiler to emit byte and half-word writes
+to APB registers causing erroneous effects.
+As a workaround those registers should be read to local variable,
+this variable altered, and then written back to hardware.
+GNAT users may not need the workaround, because of its pragma
+`Volatile_Full_Access` used in this library.
+
+## Compiler specific notes
+
+There are compiler-specific pragmas so your compiler may complain about them.
+
+
+### GNAT
+
+`Volatile_Full_Access` pragma is used on (at least writable) APB registers
+as byte- and half-wide writes are not supported by APB. Read STM docs on
+what those accesses actually do.
\ No newline at end of file
diff --git a/source/stm32-f4-exti.ads b/source/stm32-f4-exti.ads
index 24aa2fe..3a6c6a9 100644
--- a/source/stm32-f4-exti.ads
+++ b/source/stm32-f4-exti.ads
@@ -27,12 +27,18 @@ package STM32.F4.EXTI is
 	end record;
 
 	type EXTI_Registers is record
-		IMR:   Event_Set_Register with Volatile_Full_Access;
-		EMR:   Event_Set_Register with Volatile_Full_Access;
-		RTSR:  Event_Set_Register with Volatile_Full_Access;
-		FTSR:  Event_Set_Register with Volatile_Full_Access;
-		SWIER: Event_Set_Register with Volatile_Full_Access;
-		PR:    Event_Set_Register with Volatile_Full_Access;
+		IMR:   Event_Set_Register;
+		Pragma Volatile_Full_Access(IMR);
+		EMR:   Event_Set_Register;
+		Pragma Volatile_Full_Access(EMR);
+		RTSR:  Event_Set_Register;
+		Pragma Volatile_Full_Access(RTSR);
+		FTSR:  Event_Set_Register;
+		Pragma Volatile_Full_Access(FTSR);
+		SWIER: Event_Set_Register;
+		Pragma Volatile_Full_Access(SWIER);
+		PR:    Event_Set_Register;
+		Pragma Volatile_Full_Access(PR);
 	end record;
 
 	for EXTI_Registers use record
diff --git a/source/stm32-f4-pwr.ads b/source/stm32-f4-pwr.ads
index 2d312d6..2399ac9 100644
--- a/source/stm32-f4-pwr.ads
+++ b/source/stm32-f4-pwr.ads
@@ -117,8 +117,10 @@ package STM32.F4.PWR is
 	end record;
 
 	type PWR_Registers is record
-		CR  : Power_Control_Register with Volatile_Full_Access;
-		CSR : Power_Control_Status_Register with Volatile_Full_Access;
+		CR  : Power_Control_Register;
+		Pragma Volatile_Full_Access(CR);
+		CSR : Power_Control_Status_Register;
+		Pragma Volatile_Full_Access(CSR);
 	end record with Volatile;
 
 	for PWR_Registers use record
diff --git a/source/stm32-f4-syscfg.ads b/source/stm32-f4-syscfg.ads
index a835062..424e5c0 100644
--- a/source/stm32-f4-syscfg.ads
+++ b/source/stm32-f4-syscfg.ads
@@ -114,13 +114,20 @@ package STM32.F4.SysCfg is
 	end record;
 
 	type SYSCFG_Registers is record
-		MEMRMP: Memory_Remap_Register with Volatile_Full_Access;
-		PMC: Peripherial_Mode_Register with Volatile_Full_Access;
-		EXTICR1: External_Interrupt_Configuration_1.Register with Volatile_Full_Access;
-		EXTICR2: External_Interrupt_Configuration_2.Register with Volatile_Full_Access;
-		EXTICR3: External_Interrupt_Configuration_3.Register with Volatile_Full_Access;
-		EXTICR4: External_Interrupt_Configuration_4.Register with Volatile_Full_Access;
-		CMPCR: Compensation_Cell_Control_Register with Volatile_Full_Access;
+		MEMRMP: Memory_Remap_Register;
+		Pragma Volatile_Full_Access(MEMRMP);
+		PMC: Peripherial_Mode_Register;
+		Pragma Volatile_Full_Access(PMC);
+		EXTICR1: External_Interrupt_Configuration_1.Register;
+		Pragma Volatile_Full_Access(EXTICR1);
+		EXTICR2: External_Interrupt_Configuration_2.Register;
+		Pragma Volatile_Full_Access(EXTICR2);
+		EXTICR3: External_Interrupt_Configuration_3.Register;
+		Pragma Volatile_Full_Access(EXTICR3);
+		EXTICR4: External_Interrupt_Configuration_4.Register;
+		Pragma Volatile_Full_Access(EXTICR4);
+		CMPCR: Compensation_Cell_Control_Register;
+		Pragma Volatile_Full_Access(CMPCR);
 	end record;
 
 	for SYSCFG_Registers use record
diff --git a/source/stm32-f4-usart.ads b/source/stm32-f4-usart.ads
index 9c6018c..651edc9 100644
--- a/source/stm32-f4-usart.ads
+++ b/source/stm32-f4-usart.ads
@@ -226,13 +226,20 @@ package STM32.F4.USART is
 	end record;
 
 	type USART_Registers is record
-		SR: Status_Register with Volatile_Full_Access; -- Status register
-		DR: Unsigned_32 with Volatile_Full_Access; -- Data register
-		BRR: Baud_Rate_Register with Volatile_Full_Access; -- Baud rate register
-		CR1: Control_Register_1 with Volatile_Full_Access; -- Control register 1
-		CR2: Control_Register_2 with Volatile_Full_Access; -- Control register 2
-		CR3: Control_Register_3 with Volatile_Full_Access; -- Control register 3
-		GTPR: Guard_Time_and_Prescaler_Register with Volatile_Full_Access; -- Guard time and prescaler register
+		SR: Status_Register; -- Status register
+		Pragma Volatile_Full_Access(SR);
+		DR: Unsigned_32; -- Data register
+		Pragma Volatile_Full_Access(DR);
+		BRR: Baud_Rate_Register; -- Baud rate register
+		Pragma Volatile_Full_Access(BRR);
+		CR1: Control_Register_1; -- Control register 1
+		Pragma Volatile_Full_Access(CR1);
+		CR2: Control_Register_2; -- Control register 2
+		Pragma Volatile_Full_Access(CR2);
+		CR3: Control_Register_3; -- Control register 3
+		Pragma Volatile_Full_Access(CR3);
+		GTPR: Guard_Time_and_Prescaler_Register; -- Guard time and prescaler register
+		Pragma Volatile_Full_Access(GTPR);
 	end record with Volatile;
 	for USART_Registers use record
 		SR   at 16#00# range 0 .. 31;