diff --git a/TODO b/TODO
index 360005e..8e540a7 100644
--- a/TODO
+++ b/TODO
@@ -1,9 +1,11 @@
 - multi-getkey repeats (if possible, which doesn't seem likely)
-- getkey() may unwantedly repeat a key if it was triggered for multigetkey()
 
 - write and test gray engine
 - full rtc driver (time)
 - callbacks and complete user API
 
+- exhaustive save for setjmp()
+- registers that need to be saved when configuring gint
+
 _ 7305.h
 _ libc
diff --git a/ginttest.c b/ginttest.c
index 3211a45..5b5781a 100644
--- a/ginttest.c
+++ b/ginttest.c
@@ -17,7 +17,7 @@ void print_clear(void)
 {
 	char *empty_line = "                     ";
 	int i = 0;
-	while(i < 8) print(empty_line, 0, i++);
+	while(i < 8) __Print(empty_line, 0, i++);
 }
 void print(const char *str, int x, int y)
 {
@@ -66,30 +66,38 @@ void print_hexa(unsigned int n, int digits, int x, int y)
 
 /*
 	Keyboard tests.
+	The user timer reproduces the parameters of the keyboard timer.
 */
 
+void keyboard_test_timer(void)
+{
+	volatile unsigned char *state = keystate();
+
+	print_bin(state[0], 0, 1);
+	print_bin(state[1], 0, 2);
+	print_bin(state[2], 0, 3);
+	print_bin(state[3], 0, 4);
+	print_bin(state[4], 0, 5);
+
+	print_bin(state[5], 9, 1);
+	print_bin(state[6], 9, 2);
+	print_bin(state[7], 9, 3);
+	print_bin(state[8], 9, 4);
+	print_bin(state[9], 9, 5);
+}
+
 void keyboard_test(void)
 {
-/*
-		print_bin(keyboard_state[0], 0, 2);
-		print_bin(keyboard_state[1], 0, 3);
-		print_bin(keyboard_state[2], 0, 4);
-		print_bin(keyboard_state[3], 0, 5);
-		print_bin(keyboard_state[4], 0, 6);
-
-		print_bin(keyboard_state[5], 9, 2);
-		print_bin(keyboard_state[6], 9, 3);
-		print_bin(keyboard_state[7], 9, 4);
-		print_bin(keyboard_state[8], 9, 5);
-		print_bin(keyboard_state[9], 9, 6);
-*/
-
 	int x = 0;
 	char str[3];
 	int keys[4] = { 0 };
 	int i;
 
+	timer_start(TIMER_USER, 1700, TIMER_Po_256, keyboard_test_timer, 0);
+
 	print_clear();
+	print("Keyboard state:", 0, 0);
+	print("multi-getkey ^^", 6, 7);
 
 	while(1)
 	{
@@ -114,6 +122,8 @@ void keyboard_test(void)
 
 		#undef	hexa
 	}
+
+	timer_stop(TIMER_USER);
 }
 
 /*
diff --git a/ginttest.g1a b/ginttest.g1a
index ab24651..4e1da82 100644
Binary files a/ginttest.g1a and b/ginttest.g1a differ
diff --git a/icon.bmp b/icon.bmp
index c97606c..27f0e48 100644
Binary files a/icon.bmp and b/icon.bmp differ
diff --git a/include/display.h b/include/display.h
index 20e0240..00b4042 100644
--- a/include/display.h
+++ b/include/display.h
@@ -35,6 +35,12 @@ enum BlendingMode
 	Blend_Checker	= 0x10,
 };
 
+/*
+	enum ImageFormat
+	Describes the various image formats available. Colors may be encoded
+	as monochrome (1 layer) or gray (2 layers). Whatever the color map, any
+	bitmap may also have an additional alpha layer.
+*/
 enum ImageFormat
 {
 	ImageFormat_Mono	= 0x01,
@@ -45,6 +51,13 @@ enum ImageFormat
 	ImageFormat_ColorMask	= 0x0f,
 };
 
+/*
+	struct Image
+	This structure holds information about a bitmap encoded with fxconv.
+	Data is accessed using longword operations, which *requires* many
+	sizes to be multiples of 4 (structure alignment, data alignment, layer
+	size, ...).
+*/
 struct Image
 {
 	unsigned char width;
@@ -57,11 +70,12 @@ struct Image
 	const unsigned char __attribute__((aligned(4))) data[];
 
 } __attribute__((aligned(4)));
-
+// Useful shorthand for user code.
 typedef struct Image Image;
 
 
 
+// A few other constants.
 #define	DISPLAY_WIDTH	128
 #define	DISPLAY_HEIGHT	64
 
@@ -73,18 +87,31 @@ typedef struct Image Image;
 
 /*
 	display_getLocalVRAM()
-	Returns the local video ram. This address should not be used directly
-	when running the gray engine.
+	Returns the local video ram. This function always return the same
+	address.
+	The buffer returned by this function should not be used directly when
+	running the gray engine.
 
 	@return	Video ram address of the monochrome display module.
 */
 void *display_getLocalVRAM(void);
 
+/*
+	display_getCurrentVRAM()
+	Returns the current video ram. This function usually returns the
+	parameter of the last call to display_useVRAM(), unless the gray engine
+	is running (in which case the result is undefined). Returns the local
+	vram address by default.
+*/
+void *display_getCurrentVRAM(void);
+
 /*
 	display_useVRAM()
-	Changes the current video ram address. Expects a *4-aligned* 1024-byte
-	buffer.
-	Do not use this function while running the gray engine.
+	Changes the current video ram address. The argument *MUST* be a
+	4-aligned 1024 buffer ; otherwise any drawing operation will crash the
+	program.
+	This function will most likely have no effect when running the gray
+	engine.
 
 	@arg	New video ram address.
 */
@@ -169,7 +196,7 @@ void dline(int x1, int y1, int x2, int y2, enum Color color);
 
 /*
 	dimage()
-	Displays an image in the vram.
+	Displays an image in the vram. Does a real lot of optimization.
 
 	@arg	image
 	@arg	x
diff --git a/include/gint.h b/include/gint.h
index 34fc394..4468852 100644
--- a/include/gint.h
+++ b/include/gint.h
@@ -22,19 +22,38 @@ unsigned int gint_getVBR(void);
 */
 unsigned int gint_systemVBR(void);
 
+/*
+	enum RTCFrequency
+	Describes the possible frequencies available for the real-time clock
+	interrupt.
+*/
+enum RTCFrequency
+{
+	RTCFreq_500mHz	= 7,
+	RTCFreq_1Hz	= 6,
+	RTCFreq_2Hz	= 5,
+	RTCFreq_4Hz	= 4,
+	RTCFreq_16Hz	= 3,
+	RTCFreq_64Hz	= 2,
+	RTCFreq_256Hz	= 1,
+};
+
 /*
 	gint_setRTCCallback()
 	Sets the callback function for the real-time clock interrupt. If
 	frequency is non-NULL, the clock frequency is set to the given value.
+
+	@arg	callback	Callback function.
+	@arg	frequency	Interrupt frequency.
 */
-void gint_setRTCCallback(void (*callback)(void), enum GintFrequency frequency);
+void gint_setRTCCallback(void (*callback)(void), enum RTCFrequency frequency);
 
 /*
 	gint_getRTCCallback()
 	Returns the callback function. If frequency is non-NULL, it is set to
 	the current frequency value.
 */
-void (*(gint_getRTCCallback)(void))(enum GintFrequency *frequency);
+void (*gint_getRTCCallback(enum RTCFrequency *frequency))(void);
 
 
 
@@ -89,12 +108,28 @@ void gint_stop_7305(void);
 	gint()
 	Handles interrupts.
 */
-void gint(void) __attribute__((
-	section(".gint.int.entry"),
-	interrupt_handler
-));
-void gint_7705(void)		__attribute__((section(".gint.int")));
-void gint_7305(void)		__attribute__((section(".gint.int")));
+void gint(void)		__attribute__((section(".gint.int.entry"),
+				interrupt_handler));
+void gint_7705(void)	__attribute__((section(".gint.int")));
+void gint_7305(void)	__attribute__((section(".gint.int")));
+
+/*
+	gint_setRTCFrequency()
+	Sets the RTC interrupt frequency and enables interrupts.
+
+	@arg	frequency
+*/
+void gint_setRTCFrequency_7705(enum RTCFrequency frequency);
+void gint_setRTCFrequency_7305(enum RTCFrequency frequency);
+
+/*
+	gint_getRTCFrequency()
+	Returns the RTC interrupt frequency.
+
+	@return	RTC interrupt frequency.
+*/
+enum RTCFrequency gint_getRTCFrequency_7705(void);
+enum RTCFrequency gint_getRTCFrequency_7305(void);
 
 
 
diff --git a/include/mpu.h b/include/mpu.h
index eb8ddc1..a9132e6 100644
--- a/include/mpu.h
+++ b/include/mpu.h
@@ -49,4 +49,17 @@ extern enum MPU MPU_CURRENT;
 */
 enum MPU getMPU(void);
 
+
+
+//---
+//	Internal API.
+//	Referenced here for documentation purposes only. Do not call.
+//---
+
+/*
+	mpu_init()
+	Determines the MPU type and stores the result into MPU_CURRENT.
+*/
+void mpu_init(void)	__attribute__((constructor));
+
 #endif // _MPU_H
diff --git a/include/screen.h b/include/screen.h
index f54d8f8..91a85b6 100644
--- a/include/screen.h
+++ b/include/screen.h
@@ -1,6 +1,10 @@
 #ifndef	_SCREEN_H
 #define	_SCREEN_H	1
 
+//---
+//	Public API.
+//---
+
 /*
 	screen_display()
 	Displays contents on the full screen. Expects a 1024-byte buffer.
diff --git a/include/setjmp.h b/include/setjmp.h
index c43c204..2037b5e 100644
--- a/include/setjmp.h
+++ b/include/setjmp.h
@@ -17,7 +17,7 @@ typedef	unsigned int jmp_buf[16];
 
 	@arg	env	Empty jump buffer.
 */
-int	setjmp(jmp_buf env);
+int setjmp(jmp_buf env);
 
 /*
 	longjmp()
@@ -26,6 +26,6 @@ int	setjmp(jmp_buf env);
 	@arg	env	Jump buffer configure with setjmp().
 	@arg	value	setjmp() will return this integer after the jump.
 */
-void	longjmp(jmp_buf env, int value);
+void longjmp(jmp_buf env, int value);
 
 #endif	// _SETJMP_H
diff --git a/libc.a b/libc.a
index 102244a..8bf5347 100644
Binary files a/libc.a and b/libc.a differ
diff --git a/libgint.a b/libgint.a
index 82f815b..4425ae3 100644
Binary files a/libgint.a and b/libgint.a differ
diff --git a/src/display.c b/src/display.c
index 92b2315..d004b1e 100644
--- a/src/display.c
+++ b/src/display.c
@@ -41,7 +41,7 @@ static int *vram = local_vram;
 
 
 //---
-//	Local helper functions.
+//	Local functions.
 //---
 
 /*
@@ -115,14 +115,25 @@ static void getmasks(int x1, int x2, unsigned int *masks)
 //---
 
 /*
-	display_getVRAM()
-	Returns the current video ram.
+	display_getLocalVRAM()
+	Returns the local video ram.
 
 	@return	Video ram address.
 */
 void *display_getLocalVRAM(void)
 {
-	return (void*)local_vram;
+	return (void *)local_vram;
+}
+
+/*
+	display_getCurrentVRAM()
+	Returns the current vido ram.
+
+	@return	Video ram address.
+*/
+void *display_getCurrentVRAM(void)
+{
+	return (void *)vram;
 }
 
 /*
@@ -370,7 +381,7 @@ void dline(int x1, int y1, int x2, int y2, enum Color color)
 //	the same : get a part of the image in an operator, shift it depending
 //	on the drawing x-coordinate, compute a mask that indicates which bits
 //	of the operator contain information, and modify a vram long using the
-//	operator.
+//	operator and the mask.
 //---
 
 /*
diff --git a/src/gint.c b/src/gint.c
index 19198c9..e63596b 100644
--- a/src/gint.c
+++ b/src/gint.c
@@ -1,6 +1,7 @@
 #include <gint.h>
 #include <mpu.h>
 #include <gray.h>
+#include <stddef.h>
 
 //---
 //	Local variables.
@@ -10,6 +11,8 @@ static unsigned int
 	new_vbr,
 	sys_vbr;
 
+static void (*rtc_callback)(void) = NULL;
+
 
 
 //---
@@ -60,6 +63,42 @@ unsigned int gint_systemVBR(void)
 	return sys_vbr;
 }
 
+/*
+	gint_setRTCCallback()
+	Sets the callback function for the real-time clock interrupt. If
+	frequency is non-NULL, the clock frequency is set to the given value.
+
+	@arg	callback	Callback function.
+	@arg	frequency	Interrupt frequency.
+*/
+void gint_setRTCCallback(void (*callback)(void), enum RTCFrequency frequency)
+{
+	if(frequency < 1 || frequency > 7) return;
+	rtc_callback = callback;
+
+	if(isSH3())
+		gint_setRTCFrequency_7705(frequency);
+	else
+		gint_setRTCFrequency_7305(frequency);
+}
+
+/*
+	gint_getRTCCallback()
+	Returns the callback function. If frequency is non-NULL, it is set to
+	the current frequency value.
+*/
+void (*gint_getRTCCallback(enum RTCFrequency *frequency))(void)
+{
+	if(!frequency) return rtc_callback;
+
+	if(isSH3())
+		*frequency = gint_getRTCFrequency_7705();
+	else
+		*frequency = gint_getRTCFrequency_7305();
+
+	return rtc_callback;
+}
+
 /*
 	gint()
 	Handles interrupts.
diff --git a/src/gint_7305.c b/src/gint_7305.c
index 25330e9..bbdc22c 100644
--- a/src/gint_7305.c
+++ b/src/gint_7305.c
@@ -15,6 +15,35 @@
 
 
 
+//---
+//	Various MPU-dependent procedures.
+//---
+
+/*
+	gint_setRTCFrequency()
+	Sets the RTC interrupt frequency and enables interrupts.
+
+	@arg	frequency
+*/
+void gint_setRTCFrequency_7305(enum RTCFrequency frequency)
+{
+	if(frequency < 1 || frequency > 7) return;
+	RTC.RCR2.BYTE = (frequency << 4) | 0x09;
+}
+
+/*
+	gint_getRTCFrequency()
+	Returns the RTC interrupt frequency.
+
+	@return	RTC interrupt frequency.
+*/
+enum RTCFrequency gint_getRTCFrequency_7305(void)
+{
+	return (RTC.RCR2.BYTE & 0x70) >> 4;
+}
+
+
+
 //---
 //	Keyboard management.
 //---
@@ -272,15 +301,16 @@ void gint_setup_7305(void)
 {
 	gint_priority_lock_7305();
 
-	// Configuring the RTC to have a 16-Hz keyboard.
+	// Saving the RTC configuration.
 	rcr2 = RTC.RCR2.BYTE;
-	RTC.RCR2.BYTE = 0x39;
+	// Disabling RTC interrupts by default.
+	RTC.RCR2.BYTE = 0x09;
 }
 
 void gint_stop_7305(void)
 {
 	gint_priority_unlock_7305();
 
-	// Stopping the RTC interrupt.
+	// Restoring the RTC configuration.
 	RTC.RCR2.BYTE = rcr2;
 }
diff --git a/src/gint_7705.c b/src/gint_7705.c
index 563958b..4a08601 100644
--- a/src/gint_7705.c
+++ b/src/gint_7705.c
@@ -15,6 +15,35 @@
 
 
 
+//---
+//	Various MPU-dependent procedures.
+//---
+
+/*
+	gint_setRTCFrequency()
+	Sets the RTC interrupt frequency and enables interrupts.
+
+	@arg	frequency
+*/
+void gint_setRTCFrequency_7705(enum RTCFrequency frequency)
+{
+	if(frequency < 1 || frequency > 7) return;
+	RTC.RCR2.BYTE = (frequency << 4) | 0x09;
+}
+
+/*
+	gint_getRTCFrequency()
+	Returns the RTC interrupt frequency.
+
+	@return	RTC interrupt frequency.
+*/
+enum RTCFrequency gint_getRTCFrequency_7705(void)
+{
+	return (RTC.RCR2.BYTE & 0x70) >> 4;
+}
+
+
+
 //---
 //	Keyboard management.
 //---
@@ -22,7 +51,7 @@
 /*
 	kdelay()
 	Used to be a low-level sleep using the watchdog, as in the system. This
-	way seems ok at least, and it doesn't create column effects as for
+	way seems OK at least, and it doesn't create column effects as for
 	SH7305.
 */
 static void kdelay(void)
@@ -181,6 +210,7 @@ void gint_7705(void)
 //---
 
 static unsigned short iprs[8];
+static unsigned char rcr2;
 
 static void gint_priority_lock_7705(void)
 {
@@ -230,11 +260,16 @@ void gint_setup_7705(void)
 {
 	gint_priority_lock_7705();
 
-	// Configuring the RTC to have a 16-Hz keyboard.
-	RTC.RCR2.BYTE = 0x39;
+	// Saving the RTC configuration.
+	rcr2 = RTC.RCR2.BYTE;
+	// Disabling RTC interrupts by default.
+	RTC.RCR2.BYTE = 0x09;
 }
 
 void gint_stop_7705(void)
 {
 	gint_priority_unlock_7705();
+
+	// Restoring the RTC configuration.
+	RTC.RCR2.BYTE = rcr2;
 }
diff --git a/src/keyboard.c b/src/keyboard.c
index 0ec7a0e..1f44d74 100644
--- a/src/keyboard.c
+++ b/src/keyboard.c
@@ -214,7 +214,7 @@ int keylast(int *repeat_count)
 /*
 	keystate()
 	Returns the address of the keyboard state array. The returned address
-	if the handler's buffer, therefore it contains volatile data.
+	is the handler's buffer, therefore it contains volatile data.
 
 	@return	10-byte keyboard state buffer.
 */
diff --git a/src/mpu.c b/src/mpu.c
index ccc38d6..fa5fbea 100644
--- a/src/mpu.c
+++ b/src/mpu.c
@@ -63,13 +63,13 @@ enum MPU getMPU(void)
 	return MPU_Unknown;
 }
 
-static void mpu_init(void)
-	__attribute__((
-		section(".pretext"),
-		constructor
-	));
 
-static void mpu_init(void)
+
+/*
+	mpu_init()
+	Determines the MPU type and stores the result into MPU_CURRENT.
+*/
+void mpu_init(void)
 {
 	MPU_CURRENT = getMPU();
 }
diff --git a/src/timer.c b/src/timer.c
index d7afc15..77c9a9d 100644
--- a/src/timer.c
+++ b/src/timer.c
@@ -2,9 +2,14 @@
 #include <mpu.h>
 #include <stddef.h>
 
+//---
+//	Internal declarations.
+//	Timer structure and running  information (callbacks, repeats etc.)
+//---
+
 /*
 	struct Timer
-	This structure handles a running timer information.
+	This structure holds information for a running timer.
 */
 struct Timer
 {
@@ -17,7 +22,8 @@ static struct Timer timers[3] = { { NULL, 0 }, { NULL, 0 }, { NULL, 0 } };
 
 /*
 	struct mod_tmu
-	This structure allows access to a timer using its address.
+	This structure holds information about the timer unit (peripheral
+	module) registers.
 */
 struct mod_tmu
 {
@@ -48,6 +54,10 @@ struct mod_tmu
 
 
 
+//---
+//	Internal API.
+//---
+
 /*
 	timer_get()
 
@@ -57,7 +67,7 @@ struct mod_tmu
 	@arg	tmu	mod_tmu structure pointer address.
 	@arg	tstr	mod_tstr structure pointer address.
 */
-void timer_get(int timer, struct mod_tmu **tmu, unsigned char **tstr)
+static void timer_get(int timer, struct mod_tmu **tmu, unsigned char **tstr)
 {
 	// Using SH7705 information for SH-3-based MPUs.
 	if(MPU_CURRENT == MPU_SH7337 || MPU_CURRENT == MPU_SH7355)
@@ -76,6 +86,37 @@ void timer_get(int timer, struct mod_tmu **tmu, unsigned char **tstr)
 	if(tmu) *tmu += timer;
 }
 
+/*
+	timer_interrupt()
+	Handles the interrupt for the given timer.
+
+	@timer	Timer that generated the interrupt.
+*/
+void timer_interrupt(int timer)
+{
+	// Getting the timer address.
+	struct mod_tmu *tmu;
+	timer_get(timer, &tmu, NULL);
+
+	// Resetting the interrupt flag.
+	(*tmu).TCR.UNF = 0;
+
+	// Calling the callback function.
+	if(timers[timer].callback) timers[timer].callback();
+
+	// Reducing the number of repetitions left, if not infinite.
+	if(!timers[timer].repetitions) return;
+	// And stopping it if necessary.
+	if(timers[timer].repetitions == 1) timer_stop(timer);
+	else timers[timer].repetitions--;
+}
+
+
+
+//---
+//	Public API.
+//---
+
 /*
 	timer_start()
 	Configures and starts a timer.
@@ -135,28 +176,3 @@ void timer_stop(int timer)
 	// Stopping the timer.
 	*tstr &= ~byte;
 }
-
-/*
-	timer_interrupt()
-	Handles the interrupt for the given timer.
-
-	@timer	Timer that generated the interrupt.
-*/
-void timer_interrupt(int timer)
-{
-	// Getting the timer address.
-	struct mod_tmu *tmu;
-	timer_get(timer, &tmu, NULL);
-
-	// Resetting the interrupt flag.
-	(*tmu).TCR.UNF = 0;
-
-	// Calling the callback function.
-	if(timers[timer].callback) timers[timer].callback();
-
-	// Reducing the number of repetitions left, if not infinite.
-	if(!timers[timer].repetitions) return;
-	// And stopping it if necessary.
-	if(timers[timer].repetitions == 1) timer_stop(timer);
-	else timers[timer].repetitions--;
-}