diff --git a/Makefile b/Makefile
index 0789106..54a2101 100644
--- a/Makefile
+++ b/Makefile
@@ -12,7 +12,7 @@
 #---
 
 # Modules
-modules-gint	= core keyboard mmu mpu rtc screen timer \
+modules-gint	= core clock keyboard mmu mpu rtc screen timer \
 		  bopti display gray tales
 modules-libc	= setjmp string stdio stdlib time
 
@@ -173,7 +173,7 @@ mrproper: clean
 distclean: mrproper
 
 install:
-	CasioUsbUploader -f $(target-g1a) -w -l 1
+	p7 send -f $(target-g1a)
 
 
 .PHONY: all clean mrproper distclean
diff --git a/TODO b/TODO
index cbef227..39e6d9e 100644
--- a/TODO
+++ b/TODO
@@ -1,44 +1,27 @@
+Bugs to fix:
+-  Left-vram overflow when rendering text
+-  A few key hits ignored after leaving the application (could not reproduce)
+-  Lost keyboard control at startup (could not reproduce)
+-  Back-light issues
 
-                                 --------------
-                              Lots of things to do
-                                 --------------
+Simple improvements:
+-  bopti:	Monochrome bitmaps blending modes
+-  bopti:	Partial transparency
+-  clock:	Compute clock frequencies
+-  demo:	Try 284x124 at (-60, -28) (all disadvantages)
+-  display:	Rectangle-based drawing functions
+-  tales:	Test all font encodings
+-  time:	Compute CLOCKS_PER_SEC
+-  timer:	Add duration and frequency settings
+-  core:	Add VBR handlers debugging information (if possible)
+-  core:	Implement all callbacks and a complete user API
 
-  @    known bugs
-  +    simple improvements
-  -    important milestones
-  ~    needs investigation
+Modules to implement:
+-  Serial communication
+-  Sound playback and synthesizing
 
-
-@  possibility of vram left-overflow with text
-@  garbage displayed as year in the clock, possibly during edition (could not
-   reproduce)
-@  a few key hits ignored after leaving the application
-
-+  rect functions
-+  bitmap blending modes
-+  minimize use of 7705.h and 7305.h; use local structures instead
-+  partial transparency
-+  gint vs. ML with 248x124 at (-60, -28)
-+  call exit handlers
-+  compute frequencies and CLOCKS_PER_SEC
-+  test all font encodings
-
--  improve exception handler debugging information (if possible)
--  callbacks and complete user API
-
-~  packed bit fields
-~  exhaustive save for setjmp()
-~  registers that need to be saved when configuring gint
-~  possible bug when -O2'ing __attribute__((interrupt_handler))
-
-
-
-Some notes
-----------
-
-Test cases for bitmap drawing:
-- 32-alignment
-- monochrome / gray
-- small / large
-- clipping
-# blending modes
+Things to investigate:
+-  Packed bit fields alignment
+-  Registers that may need to be saved within setjmp()
+-  Registers that may need to be saved and restored by gint
+-  Possible bug when optimizing __attribute__((interrupt_handler))
diff --git a/demo/gintdemo.c b/demo/gintdemo.c
index 8e4249f..32bba87 100644
--- a/demo/gintdemo.c
+++ b/demo/gintdemo.c
@@ -305,7 +305,7 @@ void main_menu(int *category, int *app)
 		"Image rendering",
 		"Text rendering",
 		"Real-time clock",
-		"Text formatting",
+		"Clocks and timers",
 		NULL
 	};
 	const char *list_perfs[] = {
@@ -511,7 +511,7 @@ int main(void)
 			test_rtc();
 			break;
 		case 0x0106:
-//			test_printf();
+			test_timer();
 			break;
 
 		case 0x0201:
diff --git a/demo/gintdemo.h b/demo/gintdemo.h
index a7805a3..1d32bcd 100644
--- a/demo/gintdemo.h
+++ b/demo/gintdemo.h
@@ -76,10 +76,10 @@ void test_tales(void);
 void test_rtc(void);
 
 /*
-	test_printf()
-	Some text formatting.
+	test_timer()
+	Clock timer and timer precision.
 */
-void test_printf(void);
+void test_timer(void);
 
 
 
diff --git a/demo/gintdemo.ld b/demo/gintdemo.ld
index cf7bb2f..49062c9 100644
--- a/demo/gintdemo.ld
+++ b/demo/gintdemo.ld
@@ -3,12 +3,9 @@
 	output. Note how symbols romdata, bbss, ebss, bdata and edata are used
 	in the initialization routine (crt0.c) to initialize the application.
 
-	Two ram areas are specified. It happens, if I'm not wrong, that the
-	"real ram" is accessed directly while the "common" ram is accessed
-	through the mmu. The interrupt handler resides in "real ram" because it
-	couldn't execute well in ram. While SH7335 and SH7355 had no problems,
-	executing the interrupt handler in the common ram on SH7305-based new
-	models caused trouble to the OS, apparently overwriting ram data.
+	Two ram areas are specified. The "real ram" is accessed direcly while
+	the other area is virtualized. It is not possible to execute code in
+	virtualized ram.
 */
 
 OUTPUT_ARCH(sh3)
diff --git a/demo/resources/clock_7305.bmp b/demo/resources/clock_7305.bmp
new file mode 100644
index 0000000..83690f6
Binary files /dev/null and b/demo/resources/clock_7305.bmp differ
diff --git a/demo/resources/clock_7705.bmp b/demo/resources/clock_7705.bmp
new file mode 100644
index 0000000..d711160
Binary files /dev/null and b/demo/resources/clock_7705.bmp differ
diff --git a/demo/resources/clock_chars.bmp b/demo/resources/clock_chars.bmp
new file mode 100644
index 0000000..6edc348
Binary files /dev/null and b/demo/resources/clock_chars.bmp differ
diff --git a/demo/resources/opt_gray.bmp b/demo/resources/opt_gray.bmp
index a44613d..87ba1c7 100644
Binary files a/demo/resources/opt_gray.bmp and b/demo/resources/opt_gray.bmp differ
diff --git a/demo/resources/opt_timer.bmp b/demo/resources/opt_timer.bmp
new file mode 100644
index 0000000..1d7cb9c
Binary files /dev/null and b/demo/resources/opt_timer.bmp differ
diff --git a/demo/test_bopti.c b/demo/test_bopti.c
index 3b9ee45..57695d5 100644
--- a/demo/test_bopti.c
+++ b/demo/test_bopti.c
@@ -178,7 +178,6 @@ void test_bopti(void)
 			dupdate();
 		}
 
-		leave = 1;
 		do
 		{
 			leave = 1;
diff --git a/demo/test_gray.c b/demo/test_gray.c
index 55c23ef..61d06aa 100644
--- a/demo/test_gray.c
+++ b/demo/test_gray.c
@@ -11,25 +11,30 @@
 static void draw(int delay1, int delay2, int selected)
 {
 	extern Image res_opt_gray_start;
-	int *vl = gray_lightVRAM();
-	int *vd = gray_darkVRAM();
+	unsigned int *vl = gray_lightVRAM();
+	unsigned int *vd = gray_darkVRAM();
 
 	gclear();
+	locate(1, 1, "Gray engine");
 
-	for(int i = 0; i < 63; i++)
+	for(int i = 0; i < 36; i++)
 	{
-		int o = (i << 2) + 2;
-		vl[o] = vl[o + 1] = -((i & 31) < 16);
-		vd[o] = vd[o + 1] = -(i < 32);
+		int o = ((i + 12) << 2) + 2;
+		unsigned light	= -((i % 24) < 12);
+		unsigned dark	= -(i < 24);
+		vl[o]		= light >> 8;
+		vl[o + 1]	= light << 8;
+		vd[o]		= dark >> 8;
+		vd[o + 1]	= dark << 8;
 	}
 
-	locate(3, 2, "light");
-	print(3, 3, "%d", delay1);
+	locate(3, 3, "light");
+	print(4, 4, "%d", delay1);
 
 	locate(3, 5, "dark");
-	print(3, 6, "%d", delay2);
+	print(4, 6, "%d", delay2);
 
-	locate(2, selected ? 6 : 3, "\x02");
+	locate(3, selected ? 6 : 4, "\x02");
 
 	gimage(0, 56, &res_opt_gray_start);
 	gupdate();
@@ -64,10 +69,14 @@ void test_gray(void)
 			selected = !selected;
 			break;
 		case KEY_F2:
-			delays[0] = isSH3() ? 985 : 994;
-			delays[1] = 1609;
+			delays[0] = 912;
+			delays[1] = 1343;
 			break;
 		case KEY_F3:
+			delays[0] = 993;
+			delays[1] = 1609;
+			break;
+		case KEY_F4:
 			delays[0] = 860;
 			delays[1] = 1298;
 			break;
diff --git a/demo/test_rtc.c b/demo/test_rtc.c
index 93a15c6..e3c0a09 100644
--- a/demo/test_rtc.c
+++ b/demo/test_rtc.c
@@ -179,7 +179,7 @@ static void set(void)
 
 				if(n == 7)
 				{
-					int month = k + 4 * slide - 1;
+					int month = k + 4 * slide - 2;
 					set_region(&time, n, month);
 					n++;
 					slide = 0;
diff --git a/demo/test_timer.c b/demo/test_timer.c
new file mode 100644
index 0000000..9191508
--- /dev/null
+++ b/demo/test_timer.c
@@ -0,0 +1,284 @@
+#include "gintdemo.h"
+#include <stddef.h>
+#include <stdio.h>
+#include <string.h>
+
+#include <internals/timer.h>
+#include <timer.h>
+#include <display.h>
+#include <keyboard.h>
+#include <clock.h>
+#include <mpu.h>
+#include <rtc.h>
+
+static void draw(int new_tab);
+static struct ClockConfig conf;
+
+//---
+//	Timer-RTC comparison.
+//	The precision of the timer is measured by comparing it to the RTC.
+//---
+
+static volatile int elapsed_timer = -1;
+static volatile int elapsed_rtc = -1;
+
+static void timing_rtc(void)
+{
+	elapsed_rtc++;
+}
+
+static void timing_timer(void)
+{
+	elapsed_timer++;
+}
+
+static void timing_start(void)
+{
+	timer_start(TIMER_USER, clock_setting(16, Clock_Hz), TIMER_Po_4,
+		timing_timer, 0);
+	rtc_setCallback(timing_rtc, RTCFreq_16Hz);
+
+	elapsed_timer = 0;
+	elapsed_rtc = 0;
+}
+
+
+
+//---
+//	Drawing.
+//---
+
+/*
+	small_text()
+	Renders small text using a minimalist bitmap-based font.
+*/
+static void small_text(int x, int y, const char *text, int alignment)
+{
+	extern Image res_clock_chars_start;
+	Image *chars = &res_clock_chars_start;
+	const char *table = "0123456789kMHz*/";
+
+	if(alignment) x -= 2 * strlen(text) - 1, y -= 2;
+	int c;
+
+	while(*text)
+	{
+		const char *ptr = strchr(table, *text++);
+		if(!ptr) continue;
+		c = ptr - table;
+
+		dimage_part(x, y, chars, c << 2, 0, 3, 5);
+		x += 4;
+	}
+}
+
+/*
+	getFreq()
+	Prints the given frequency in a string on the form:
+
+		332kHz
+		<-><->
+		 3  3
+
+	There are 1, 2 or 3 characters for the value, and 2 or 3
+	characters for the unit. The string is compacted.
+*/
+void getFreq(char *str, int freq)
+{
+	if(freq < 1000)
+	{
+		sprintf(str, "%dHz", freq);
+		return;
+	}
+	if(freq < 1000000)
+	{
+		sprintf(str, "%dkHz", (freq + 500) / 1000);
+		return;
+	}
+	sprintf(str, "%dMHz", (freq + 500000) / 1000000);
+}
+
+/*
+	dislay_freq()
+	Displays a frequency value a unit, in an simple form.
+*/
+static void display_freq(int x, int y, int freq)
+{
+	int ratio, letter, dot, i;
+	char buffer[10];
+
+	if(freq <= 0)
+	{
+		dtext(x, y, "Unknown");
+		return;
+	}
+	if(freq < 10000)
+	{
+		dprint(x, y, "%5d", freq);
+		small_text(x + 31, y + 2, "Hz", 0);
+		return;
+	}
+
+	if(freq < 10000000) ratio = 1, letter = 'k';
+	else ratio = 1000, letter = 'M';
+
+	dot = 1 + (freq >= 10000 * ratio) + (freq >= 100000 * ratio);
+	freq += (ratio * (1 + 9 * (dot >= 2) + 90 * (dot >= 3))) / 2;
+	snprintf(buffer, 6, "%d", freq);
+
+	for(i = 4; i > dot; i--) buffer[i] = buffer[i - 1];
+	buffer[dot] = '.';
+
+	dprint(x, y, buffer);
+	sprintf(buffer, "%cHz", letter);
+	small_text(x + 31, y + 2, buffer, 0);
+}
+
+/*
+	draw()
+	Draws the test interface.
+*/
+static void draw(int tab)
+{
+	extern Image res_opt_timer_start;
+	extern Image res_clock_7705_start;
+	extern Image res_clock_7305_start;
+
+	char buffer[16];
+
+	dclear();
+	dimage(0, 56, &res_opt_timer_start);
+
+	if(!tab)
+	{
+		locate(1, 1, "Clock frequency");
+		dtext(7, 20, "B\x1e");
+		display_freq(24, 20, conf.Bphi_f);
+		dtext(7, 28, "I\x1e");
+		display_freq(24, 28, conf.Iphi_f);
+		dtext(7, 36, "P\x1e");
+		display_freq(24, 36, conf.Pphi_f);
+
+		if(isSH3())
+		{
+			dimage(64, 0, &res_clock_7705_start);
+
+			getFreq(buffer, conf.CKIO_f);
+			small_text(84, 16, buffer, 1);	
+
+			sprintf(buffer, "*%d", conf.PLL1);
+			small_text(84, 34, buffer, 1);
+
+			if(conf.Iphi_div1 == 1)
+				dline(85, 43, 99, 43, Color_Black);
+			else
+			{
+				sprintf(buffer, "/%d", conf.Iphi_div1);
+				small_text(89, 41, buffer, 0);
+			}
+			if(conf.Pphi_div1 == 1)
+				dline(85, 50, 99, 50, Color_Black);
+			else
+			{
+				sprintf(buffer, "/%d", conf.Pphi_div1);
+				small_text(89, 48, buffer, 0);
+			}
+		}
+		else
+		{
+			dimage(64, 0, &res_clock_7305_start);
+
+			getFreq(buffer, conf.RTCCLK_f);
+			small_text(84, 14, buffer, 1);
+	
+			sprintf(buffer, "*%d", conf.FLL);
+			small_text(84, 25, buffer, 1);
+
+			sprintf(buffer, "*%d", conf.PLL);
+			small_text(84, 36, buffer, 1);
+
+			sprintf(buffer, "/%d", conf.Bphi_div1);
+			small_text(89, 43, buffer, 0);
+			sprintf(buffer, "/%d", conf.Iphi_div1);
+			small_text(89, 50, buffer, 0);
+			sprintf(buffer, "/%d", conf.Pphi_div1);
+			small_text(89, 57, buffer, 0);
+		}
+	}
+	else
+	{
+		locate(1, 1, "Timer/RTC comparison");
+
+		locate(2, 3, "Timer");
+		if(elapsed_timer >= 0) print(12, 3, "%04x", elapsed_timer);
+		else locate(12, 3, "...");
+
+		locate(2, 4, "RTC");
+		if(elapsed_rtc >= 0) print(12, 4, "%04x", elapsed_rtc);
+		else locate(12, 4, "...");
+
+		// We define the accuracy of the timer as the square of the
+		// ratio between the two counters.
+		locate(2, 5, "Accuracy");
+		if(elapsed_rtc > 0 && elapsed_timer > 0)
+		{
+			int ratio;
+			if(elapsed_timer <= elapsed_rtc)
+				ratio = (10000 * elapsed_timer) / elapsed_rtc;
+			else
+				ratio = (10000 * elapsed_rtc) / elapsed_timer;
+			ratio = (ratio * ratio) / 10000;
+
+			print(12, 5, "%d.%02d %%", ratio / 100, ratio % 100);
+		}
+		else locate(12, 5, "...");
+	}
+
+	dupdate();
+}
+
+
+
+//---
+//	Timer/clock test.
+//---
+
+/*
+	test_timer()
+	Clock timer and timer precision.
+*/
+void test_timer(void)
+{
+	int tab = 0;
+
+	clock_measure();
+	clock_measure_end();
+
+	conf = clock_config();
+
+	elapsed_timer	= -1;
+	elapsed_rtc	= -1;
+	rtc_setCallback(timing_start, RTCFreq_16Hz);
+
+	text_configure(NULL, Color_Black);
+
+	while(1)
+	{
+		draw(tab);
+
+		switch(getkey_opt(Getkey_NoOption, 1))
+		{
+		case KEY_EXIT:
+			timer_stop(TIMER_USER);
+			rtc_setCallback(NULL, RTCFreq_1Hz);
+			return;
+
+		case KEY_F1:
+			tab = 0;
+			break;
+		case KEY_F2:
+			tab = 1;
+			break;
+		}
+	}
+}
diff --git a/include/clock.h b/include/clock.h
new file mode 100644
index 0000000..744d341
--- /dev/null
+++ b/include/clock.h
@@ -0,0 +1,123 @@
+//---
+//
+//	gint core module: clock
+//
+//	Measures the frequency of the MPU clocks. This module assumes that the
+//	clock mode is 3 on SH7305 (as does FTune).
+//
+//---
+
+//---
+//	Some type declarations.
+//---
+
+enum Clock
+{
+	Clock_CKIO 	= 0,	// SH7705
+	Clock_RTCCLK	= 1,	// SH7305
+	Clock_Bphi	= 2,
+	Clock_Iphi	= 3,
+	Clock_Pphi	= 4,
+};
+
+enum ClockUnit
+{
+	Clock_us	= 0,
+	Clock_ms	= 1,
+	Clock_s		= 2,
+
+	Clock_Hz	= 10,
+	Clock_kHz	= 11,
+	Clock_MHz	= 12,
+};
+
+struct ClockConfig
+{
+	union
+	{
+		int PLL1;	// SH7705
+		int FLL;	// SH7305
+	};
+	union
+	{
+		int PLL2;	// SH7705
+		int PLL;	// SH7305
+	};
+
+	int Bphi_div1;
+	int Iphi_div1;
+	int Pphi_div1;
+
+	union
+	{
+		int CKIO_f;	// SH7705
+		int RTCCLK_f;	// SH7305
+	};
+
+	int Bphi_f;
+	int Iphi_f;
+	int Pphi_f;
+};
+
+//---
+//	Public API.
+//---
+
+/*
+	clock_frequency()
+	Returns the approximate frequency, in Hz, of the given clock. The
+	measurements need to have been done. Returns a negative number on
+	error.
+*/
+int clock_frequency(enum Clock clock);
+
+/*
+	clock_setting()
+	Returns the P_phi / 4 timer setting that will last for the given time.
+	Several units can be used. Be aware that the result is approximate, and
+	very high frequencies or very short delays will yield important errors.
+*/
+int clock_setting(int duration, enum ClockUnit unit);
+
+/*
+	clock_config()
+	Returns a copy of the clock configuration.
+*/
+struct ClockConfig clock_config(void);
+
+/*
+	sleep()
+	Sleeps until an interrupt is accepted.
+*/
+void sleep(void);
+
+/*
+	sleep_us()
+	Sleeps for the given number of us using the user timer. The result will
+	always be slightly less than required.
+*/
+void sleep_us(int us_delay);
+
+
+
+//---
+//	Internal API.
+//	Referenced for documentation purposes only. Do not use.
+//---
+
+/*
+	clock_measure()
+	Begins the frequency measurements. The measurements will end
+	automatically. While doing measurements, do not use the RTC interrupt
+	or the user timer.
+	Call clock_measure_end() to wait until the measurements are finished.
+	It is possible to execute code during the measurements, so that less
+	time is spent.
+*/
+void clock_measure(void);
+
+/*
+	clock_measure_end()
+	Waits until the measurements are finished. This may be immediate.
+*/
+void clock_measure_end(void);
diff --git a/include/gray.h b/include/gray.h
index c77cf83..625c84f 100644
--- a/include/gray.h
+++ b/include/gray.h
@@ -65,11 +65,11 @@ void gray_getDelays(int *light, int *dark);
 
 	values		stability	stripes		colors
 	---------------------------------------------------------
-	860, 1298	excellent	worst static	good
-	912, 1343	bad		none		very good
-	993, 1609	medium		light fast	good       (default)
+	 860, 1298	excellent	worst static	good
+	 912, 1343	bad		none		very good  (default)
+	 993, 1609	medium		light fast	good
+	1325, 1607	bad		light fast	excellent
 	---------------------------------------------------------
-
 */
 void gray_setDelays(int light, int dark);
 
diff --git a/include/mpu.h b/include/mpu.h
index 33a08c8..fd4a498 100644
--- a/include/mpu.h
+++ b/include/mpu.h
@@ -2,11 +2,20 @@
 //
 //	gint core module: mpu
 //
-//	Determines which kind of MPU is running the program. This module only
-//	provides the following test:
+//	Determines which kind of MPU is running the program. This module
+//	provides macro tests isSH3(), isSH4(), and the identifier of the MPU,
+//	which is stored in a global variable MPU_CURRENT.
 //
-//	if(isSH3()) { ... }
-//	else { ... }
+//	If you need to do MPU-dependant jobs, prefer the following alternative:
+//
+//		if(isSH3())
+//		{
+//			...
+//		}
+//		else
+//		{
+//			...
+//		}
 //
 //---
 
diff --git a/src/clock/clock.c b/src/clock/clock.c
new file mode 100644
index 0000000..b785a07
--- /dev/null
+++ b/src/clock/clock.c
@@ -0,0 +1,288 @@
+#include <clock.h>
+#include <timer.h>
+#include <internals/timer.h>
+#include <rtc.h>
+#include <stddef.h>
+#include <mpu.h>
+
+static struct ClockConfig conf = {
+	.FLL = -1, .PLL = -1,
+	.Bphi_div1 = -1, .Iphi_div1 = -1, .Pphi_div1 = -1,
+	.CKIO_f = -1,
+	.Bphi_f = -1, .Iphi_f = -1, .Pphi_f = -1
+};
+
+/*
+	clock_frequency()
+	Returns the approximate frequency, in Hz, of the given clock. The
+	measurements need to have been done. Returns a negative number on
+	error.
+*/
+int clock_frequency(enum Clock clock)
+{
+	switch(clock)
+	{
+	case Clock_CKIO:
+		return conf.CKIO_f;
+	case Clock_RTCCLK:
+		return conf.RTCCLK_f;
+	case Clock_Bphi:
+		return conf.Bphi_f;
+	case Clock_Iphi:
+		return conf.Iphi_f;
+	case Clock_Pphi:
+		return conf.Pphi_f;
+
+	default:
+		return -2;
+	}
+}
+
+/*
+	clock_setting()
+	Returns the P_phi / 4 timer setting that will last for the given time.
+	Several units can be used. Be aware that the result is approximate, and
+	very high frequencies or very short delays will yield important errors.
+*/
+int clock_setting(int duration, enum ClockUnit unit)
+{
+	if(conf.Pphi_f <= 0) return -1;
+	int f = conf.Pphi_f >> 2;
+
+	switch(unit)
+	{
+	case Clock_us:
+		return (duration * f) / 1000000;
+	case Clock_ms:
+		return (duration * f) / 1000;
+	case Clock_s:
+		return (duration * f);
+
+	case Clock_Hz:
+		return f / duration;
+	case Clock_kHz:
+		return f / (duration * 1000);
+	case Clock_MHz:
+		return f / (duration * 1000000);
+
+	default:
+		return -1;
+	}
+}
+
+/*
+	clock_config()
+	Returns a copy of the clock configuration.
+*/
+struct ClockConfig clock_config(void)
+{
+	return conf;
+}
+
+/*
+	sleep()
+	Sleeps until an interrupt is accepted.
+*/
+void sleep(void)
+{
+	__asm__(
+		"sleep\n\t"
+	);
+}
+
+/*
+	sleep_us()
+	Sleeps for the given number of us using the user timer. The result will
+	always be slightly less than required.
+*/
+
+static volatile int sleep_us_done = 0;
+
+static void sleep_us_callback(void)
+{
+	sleep_us_done = 1;
+}
+
+void sleep_us(int us_delay)
+{
+	sleep_us_done = 0;
+	timer_start(TIMER_USER, clock_setting(us_delay, Clock_us), TIMER_Po_4,
+		sleep_us_callback, 1);
+	do sleep();
+	while(!sleep_us_done);
+}
+
+
+
+//---
+//	Clock frequency measurements -- Public API.
+//---
+
+// Indicates whether the measurements are finished.
+static volatile int clock_measure_done = 0;
+// Once again SH7705 and SH7305 need different methods...
+static void clock_measure_7705();
+static void clock_compute_7305();
+
+/*
+	clock_measure()
+	Measures or computes the clock frequencies.
+*/
+void clock_measure(void)
+{
+	// On SH7705 we cannot have the value of CKIO simply, so we measure
+	// P_phi using a timer/RTC combination, and we deduce CKIO.
+	if(isSH3())
+	{
+		// We prepare the timer manually, without starting it, so that
+		// we only have to push the running bit to start it when the
+		// measurements begin. This might look of little effect but the
+		// timer configuration time (lost from the measurement) would
+		// make the precision no more than 97-98%.
+		volatile struct mod_tmu *tmu;
+		timer_get(TIMER_USER, &tmu, NULL);
+
+		tmu->TCOR	= 0xffffffff;
+		tmu->TCNT	= tmu->TCOR;
+		tmu->TCR.TPSC	= TIMER_Po_4;
+
+		tmu->TCR.UNF	= 0;
+		tmu->TCR.UNIE	= 1;
+		tmu->TCR.CKEG	= 0;
+
+		timers[TIMER_USER].callback	= NULL;
+		timers[TIMER_USER].repeats	= 0;
+
+		rtc_setCallback(clock_measure_7705, RTCFreq_256Hz);
+	}
+
+	// On SH7305, assuming clock mode 3, we can compute the clock
+	// frequencies because we know that RTC_CLK oscillates at 32768 Hz.
+	else
+	{
+		clock_compute_7305();
+		clock_measure_done = 1;
+	}
+}
+
+/*
+	clock_measure_end()
+	Waits until the measurements are finished. This may be immediate.
+*/
+void clock_measure_end(void)
+{
+	while(!clock_measure_done) sleep();
+}
+
+//---
+//	Clock frequency measurements -- SH7305.
+//---
+
+/*
+	clock_compute_7305()
+	Computes the clock frequencies according to the CPG parameters.
+*/
+static void clock_compute_7305(void)
+{
+	volatile unsigned int *FRQCRA	= (void *)0xa4150000;
+	volatile unsigned int *PLLCR	= (void *)0xa4150024;
+	volatile unsigned int *FLLFRQ	= (void *)0xa4150050;
+
+	// Surely the documentation of SH7724 does not meet the specification
+	// if SH7305 for the PLL setting, because the register accepts other
+	// values than the ones specified by SH7724. The formula given by
+	// Sentaro21 (thanks again!) yields good results though.
+	int pll = (*FRQCRA >> 24) & 0x3f;	// Raw setting
+	pll = pll + 1;				// Resulting multiplier
+	conf.PLL = pll;
+
+	// This one is simpler. The FLL ratio is actually the setting value.
+	int fll = *FLLFRQ & 0x7ff;		// Raw setting = multiplier
+	if(*FLLFRQ & (1 << 14)) fll >>= 1;	// Halve-output flag
+	conf.FLL = fll;
+
+	// The divider1 ratios are NOT those of SH7724. The relation between
+	// the values below and the divider ratios is given by Sentaro21
+	// (thanks to him!) and satisfies ratio = 1 / (2 ** (setting + 1)).
+	int div1_bphi = (*FRQCRA >>  8) & 0xf;
+	int div1_iphi = (*FRQCRA >> 20) & 0xf;
+	int div1_pphi = (*FRQCRA      ) & 0xf;
+
+	conf.Bphi_div1 = 1 << (div1_bphi + 1);
+	conf.Iphi_div1 = 1 << (div1_iphi + 1);
+	conf.Pphi_div1 = 1 << (div1_pphi + 1);
+
+	// Computing the frequency of the signal, which is input to divider 1.
+	int base = 32768;
+	if(*PLLCR & (1 << 12)) base *= fll;
+	if(*PLLCR & (1 << 14)) base *= pll;
+
+	conf.RTCCLK_f	= 32768;
+	conf.Bphi_f	= base >> (div1_bphi + 1);
+	conf.Iphi_f	= base >> (div1_iphi + 1);
+	conf.Pphi_f	= base >> (div1_pphi + 1);
+}
+
+//---
+//	Clock frequency measurements -- SH7705.
+//---
+
+/*
+	clock_measure_7705_finalize()
+	Given the number of P_phi / 4 timer ticks elapsed between two RTC
+	256 Hz interrupts, determines the clock configuration.
+*/
+static void clock_measure_7705_finalize(int elapsed)
+{
+	volatile unsigned int *FRQCR	= (void *)0xffffff80;
+
+	conf.Pphi_f	= elapsed * 4 * 256;
+	if(conf.Pphi_f <= 0) return;
+
+	conf.PLL1	= ((*FRQCR >> 8) & 0x03) + 1;
+	conf.PLL2	= -1;
+
+	conf.Bphi_div1	= 0;
+	conf.Iphi_div1	= ((*FRQCR >> 4) & 0x03) + 1;
+	conf.Pphi_div1	= ((*FRQCR     ) & 0x03) + 1;
+
+	conf.CKIO_f	= (conf.Pphi_f * conf.Pphi_div1) / conf.PLL1;
+	conf.Bphi_f	= conf.CKIO_f;
+	conf.Iphi_f	= (conf.CKIO_f * conf.PLL1) / conf.Iphi_div1;
+}
+
+/*
+	clock_measure_7705_callback()
+	Starts measurements. Measurements will end automatically. Do not use
+	RTC interrupt or the user timer will doing measurements.
+	Call clock_measure_end() when you need to use those, to ensure
+	measurements are finished.
+*/
+static void clock_measure_7705_callback(void)
+{
+	timer_stop(TIMER_USER);
+	rtc_setCallback(NULL, RTCFreq_1Hz);
+
+	volatile struct mod_tmu *tmu;
+	timer_get(TIMER_USER, &tmu, NULL);
+	int elapsed = 0xffffffff - tmu->TCNT;
+
+	clock_measure_7705_finalize(elapsed);
+	clock_measure_done = 1;
+}
+
+/*
+	clock_measure_7705()
+	Programs the clock measurements. We need to have the user timer and the
+	RTC synchronized for this operation, so we wait for an RTC interrupt
+	and we prepare the timer beforehand to avoid losing processor time in
+	configuring the registers.
+*/
+static void clock_measure_7705(void)
+{
+	volatile unsigned char *tstr;
+	timer_get(TIMER_USER, NULL, &tstr);
+
+	*tstr |= (1 << TIMER_USER);
+	rtc_setCallback(clock_measure_7705_callback, RTCFreq_256Hz);
+}
diff --git a/src/core/crt0.c b/src/core/crt0.c
index ab92620..15da267 100644
--- a/src/core/crt0.c
+++ b/src/core/crt0.c
@@ -3,6 +3,7 @@
 #include <setjmp.h>
 
 #include <gint.h>
+#include <clock.h>
 #include <internals/mmu.h>
 
 void	__Hmem_SetMMU(unsigned int, unsigned int, int);
@@ -57,8 +58,14 @@ int start(void)
 
 	mmu_pseudoTLBInit();
 
-	// Initializing everything.
+	// Initializing gint.
 	gint_init();
+
+	// Measure clock frequencies.
+	clock_measure();
+	clock_measure_end();
+
+	// Calling global constructors.
 	init();
 
 
diff --git a/src/core/gint.c b/src/core/gint.c
index ec3a2cb..4dcf136 100644
--- a/src/core/gint.c
+++ b/src/core/gint.c
@@ -113,7 +113,7 @@ void gint_quit(void)
 #define print(str, x, y) dtext(6 * (x) - 5, 8 * (y) - 7, str)
 #define hexdigit(n) ((n) + '0' + 39 * ((n) > 9))
 
-void hex(unsigned int x, int digits, char *str)
+static void hex(unsigned int x, int digits, char *str)
 {
 	str[0] = '0';
 	str[1] = 'x';
@@ -127,6 +127,13 @@ void hex(unsigned int x, int digits, char *str)
 	}
 }
 
+static void reverse(void)
+{
+	int *vram = display_getCurrentVRAM();
+	int i;
+	for(i = 0; i < 36; i++) vram[i] = ~vram[i];
+}
+
 /*
 	gint_exc()
 	Handles exceptions.
@@ -144,7 +151,7 @@ void gint_exc(void)
 
 	dclear();
 	print("Exception raised!", 3, 1);
-	dreverse_area(0, 0, 127, 8);
+	reverse();
 	print(gint_strerror(0), 2, 3);
 
 	print("expevt", 2, 4);
@@ -181,7 +188,7 @@ void gint_tlb(void)
 
 	dclear();
 	print("TLB error!", 6, 1);
-	dreverse_area(0, 0, 127, 8);
+	reverse();
 	print(gint_strerror(1), 2, 3);
 
 	print("expevt", 2, 4);
diff --git a/src/core/syscalls.s b/src/core/syscalls.s
index 621a84a..ffe3a43 100644
--- a/src/core/syscalls.s
+++ b/src/core/syscalls.s
@@ -7,7 +7,6 @@
 
 	.global	___GLibAddinAplExecutionCheck
 	.global	_malloc
-	.global	_calloc
 	.global	_free
 
 
diff --git a/src/display/font_system.bmp b/src/display/font_system.bmp
index 5e7a0a7..cee82be 100644
Binary files a/src/display/font_system.bmp and b/src/display/font_system.bmp differ
diff --git a/src/gray/gray_engine.c b/src/gray/gray_engine.c
index 7938891..639c750 100644
--- a/src/gray/gray_engine.c
+++ b/src/gray/gray_engine.c
@@ -152,6 +152,6 @@ void gray_init(void)
 	vrams[2] = (const void *)internal_vrams[1];
 	vrams[3] = (const void *)internal_vrams[2];
 
-	delays[0] = isSH3() ? 985 : 994;
-	delays[1] = 1609;
+	delays[0] = 912;
+	delays[1] = 1343;
 }
diff --git a/src/keyboard/keyboard_config.c b/src/keyboard/keyboard_config.c
index f3a9361..f657479 100644
--- a/src/keyboard/keyboard_config.c
+++ b/src/keyboard/keyboard_config.c
@@ -1,5 +1,7 @@
 #include <internals/keyboard.h>
 #include <keyboard.h>
+#include <clock.h>
+#include <timer.h>
 
 /*
 	keyboard_setFrequency()
@@ -7,6 +9,9 @@
 */
 void keyboard_setFrequency(int frequency)
 {
+	int setting = clock_setting(frequency, Clock_Hz);
+	if(setting <= 0) return;
+	timer_reload(TIMER_KEYBOARD, setting);
 }
 
 /*
diff --git a/src/keyboard/keyboard_interrupt.c b/src/keyboard/keyboard_interrupt.c
index 4273445..c75c542 100644
--- a/src/keyboard/keyboard_interrupt.c
+++ b/src/keyboard/keyboard_interrupt.c
@@ -1,6 +1,7 @@
 #include <keyboard.h>
 #include <timer.h>
 #include <mpu.h>
+#include <clock.h>
 
 #include <internals/keyboard.h>
 
@@ -42,7 +43,8 @@ void keyboard_interrupt(void)
 */
 void keyboard_init(void)
 {
-	timer_start(TIMER_KEYBOARD, 1700, TIMER_Po_256, keyboard_interrupt, 0);
+	int delay = clock_setting(16, Clock_Hz);
+	timer_start(TIMER_KEYBOARD, delay, TIMER_Po_4, keyboard_interrupt, 0);
 }
 
 /*
diff --git a/src/keyboard/sleep.c b/src/keyboard/sleep.c
deleted file mode 100644
index 8e71e84..0000000
--- a/src/keyboard/sleep.c
+++ /dev/null
@@ -1,13 +0,0 @@
-#include <internals/keyboard.h>
-
-/*
-	sleep()
-	Puts the CPU to sleep and waits for an interrupt.
-*/
-void sleep(void)
-{
-	__asm__
-	(
-		"sleep\n\t"
-	);
-}
diff --git a/src/mmu/pseudoTLBInit.c b/src/mmu/pseudoTLBInit.c
index d9e827b..b27d60d 100644
--- a/src/mmu/pseudoTLBInit.c
+++ b/src/mmu/pseudoTLBInit.c
@@ -1,5 +1,7 @@
 #include <internals/mmu.h>
 
+#pragma GCC diagnostic ignored "-Wunused-but-set-variable"
+
 /*
 	mmu_pseudoTLBInit()
 	We need the system to fill the TLB for us, so that it knows what
@@ -23,3 +25,5 @@ void mmu_pseudoTLBInit(void)
 		address += 0x1000;
 	}
 }
+
+#pragma GCC diagnostic pop
diff --git a/src/stdio/snprintf.c b/src/stdio/snprintf.c
index eed74db..6c5eb20 100644
--- a/src/stdio/snprintf.c
+++ b/src/stdio/snprintf.c
@@ -12,7 +12,8 @@ int snprintf(char *str, size_t size, const char *format, ...)
 	va_start(args, format);
 
 	int x = __printf(size, format, args);
-	strncpy(str, __stdio_buffer, size);
+	memcpy(str, __stdio_buffer, x + 1);
+		
 
 	va_end(args);
 	return x;
diff --git a/src/stdio/sprintf.c b/src/stdio/sprintf.c
index a283635..f0a018e 100644
--- a/src/stdio/sprintf.c
+++ b/src/stdio/sprintf.c
@@ -12,7 +12,7 @@ int sprintf(char *str, const char *format, ...)
 	va_start(args, format);
 
 	int x = __printf(0, format, args);
-	strncpy(str, __stdio_buffer, __stdio_buffer_size);
+	memcpy(str, __stdio_buffer, x + 1);
 
 	va_end(args);
 	return x;
diff --git a/src/stdio/stdio_format.c b/src/stdio/stdio_format.c
index c7db02f..5a8ecfb 100644
--- a/src/stdio/stdio_format.c
+++ b/src/stdio/stdio_format.c
@@ -401,8 +401,7 @@ int __printf(size_t size, const char *string, va_list args)
 	struct Format format;
 
 	// Avoiding overflow by adjusting the size argument.
-	if(!size || size > __stdio_buffer_size)
-		size = __stdio_buffer_size;
+	if(!size || size > __stdio_buffer_size) size = __stdio_buffer_size;
 
 	// Initializing character() variables.
 	written	= 0;
diff --git a/src/stdio/vsnprintf.c b/src/stdio/vsnprintf.c
index 5cc13e3..0bfafd4 100644
--- a/src/stdio/vsnprintf.c
+++ b/src/stdio/vsnprintf.c
@@ -9,7 +9,7 @@
 int vsnprintf(char *str, size_t size, const char *format, va_list args)
 {
 	int x = __printf(size, format, args);
-	strncpy(str, __stdio_buffer, size);
+	memcpy(str, __stdio_buffer, x + 1);
 
 	return x;
 }
diff --git a/src/stdio/vsprintf.c b/src/stdio/vsprintf.c
index 448c9da..0571fc0 100644
--- a/src/stdio/vsprintf.c
+++ b/src/stdio/vsprintf.c
@@ -9,7 +9,7 @@
 int vsprintf(char *str, const char *format, va_list args)
 {
 	int x = __printf(0, format, args);
-	strncpy(str, __stdio_buffer, __stdio_buffer_size);
+	memcpy(str, __stdio_buffer, x + 1);
 
 	return x;
 }
diff --git a/src/tales/gprint.c b/src/tales/gprint.c
deleted file mode 100644
index f67f3c1..0000000
--- a/src/tales/gprint.c
+++ /dev/null
@@ -1,4 +0,0 @@
-#include <internals/tales.h>
-#include <internals/stdio.h>
-#include <stdarg.h>
-
diff --git a/src/tales/tales_gray.c b/src/tales/tales_gray.c
new file mode 100644
index 0000000..4b9b02a
--- /dev/null
+++ b/src/tales/tales_gray.c
@@ -0,0 +1,45 @@
+#include <internals/tales.h>
+#include <display.h>
+#include <gray.h>
+
+void operate_gray(OPERATE_ARGS)
+{
+	int *vl = gray_lightVRAM();
+	int *vd = gray_darkVRAM();
+	int vram_offset = (x >> 5) + (y << 2);
+	uint32_t op;
+	int i;
+
+	for(i = 0; i < height; i++)
+	{
+		op = operators[i];
+
+		switch(color)
+		{
+		case Color_White:
+			vl[vram_offset] &= ~op;
+			vd[vram_offset] &= ~op;
+			break;
+		case Color_Light:
+			vl[vram_offset] |= op;
+			vd[vram_offset] &= ~op;
+			break;
+		case Color_Dark:
+			vl[vram_offset] &= ~op;
+			vd[vram_offset] |= op;
+			break;
+		case Color_Black:
+			vl[vram_offset] |= op;
+			vd[vram_offset] |= op;
+			break;
+		case Color_Invert:
+			vl[vram_offset] ^= op;
+			vd[vram_offset] ^= op;
+			break;
+		default:
+			break;
+		}
+
+		vram_offset += 4;
+	}
+}
diff --git a/src/tales/tales_internals.c b/src/tales/tales_internals.c
index 4cb412a..dbef3dd 100644
--- a/src/tales/tales_internals.c
+++ b/src/tales/tales_internals.c
@@ -120,47 +120,6 @@ void operate_mono(OPERATE_ARGS)
 		vram_offset += 4;
 	}
 }
-void operate_gray(OPERATE_ARGS)
-{
-	int *vl = gray_lightVRAM();
-	int *vd = gray_darkVRAM();
-	int vram_offset = (x >> 5) + (y << 2);
-	uint32_t op;
-	int i;
-
-	for(i = 0; i < height; i++)
-	{
-		op = operators[i];
-
-		switch(color)
-		{
-		case Color_White:
-			vl[vram_offset] &= ~op;
-			vd[vram_offset] &= ~op;
-			break;
-		case Color_Light:
-			vl[vram_offset] |= op;
-			vd[vram_offset] &= ~op;
-			break;
-		case Color_Dark:
-			vl[vram_offset] &= ~op;
-			vd[vram_offset] |= op;
-			break;
-		case Color_Black:
-			vl[vram_offset] |= op;
-			vd[vram_offset] |= op;
-			break;
-		case Color_Invert:
-			vl[vram_offset] ^= op;
-			vd[vram_offset] ^= op;
-			break;
-		default:
-			break;
-		}
-
-		vram_offset += 4;
-	}
-}
 
 /*
 	update()
diff --git a/src/tales/tales_text.c b/src/tales/tales_text.c
index 8b7977c..3729f7d 100644
--- a/src/tales/tales_text.c
+++ b/src/tales/tales_text.c
@@ -1,9 +1,6 @@
 #include <internals/tales.h>
 #include <tales.h>
 
-#include <display.h>
-#include <gray.h>
-
 /*
 	dtext()
 	Prints the given string, without any analysis.