diff --git a/src/devices/machine/clock.cpp b/src/devices/machine/clock.cpp
index 803e3d3a55f..4bd89fe791a 100644
--- a/src/devices/machine/clock.cpp
+++ b/src/devices/machine/clock.cpp
@@ -12,9 +12,6 @@ pulse width (active time) can be set directly with set_pulse_width.
 
 Output signal at machine start is right after falling edge.
 
-TODO:
-- add one-shot trigger? eg. monostable 555
-
 */
 
 #include "emu.h"
diff --git a/src/mame/drivers/conchess.cpp b/src/mame/drivers/conchess.cpp
index 19ae4c19d74..e2bea9699dc 100644
--- a/src/mame/drivers/conchess.cpp
+++ b/src/mame/drivers/conchess.cpp
@@ -228,7 +228,7 @@ void conchess_state::concstd(machine_config &config)
 	M6502(config, m_maincpu, 4_MHz_XTAL/2);
 	m_maincpu->set_addrmap(AS_PROGRAM, &conchess_state::main_map);
 
-	const attotime irq_period = attotime::from_hz(4_MHz_XTAL/2 / 0x1000);
+	const attotime irq_period = attotime::from_hz(4_MHz_XTAL / 0x2000);
 	m_maincpu->set_periodic_int(FUNC(conchess_state::irq0_line_assert), irq_period);
 
 	SENSORBOARD(config, m_board).set_type(sensorboard_device::MAGNETS);
@@ -244,7 +244,7 @@ void conchess_state::concstd(machine_config &config)
 
 	/* sound hardware */
 	SPEAKER(config, "mono").front_center();
-	BEEP(config, m_beeper, 4_MHz_XTAL/2 / 0x200);
+	BEEP(config, m_beeper, 4_MHz_XTAL / 0x400);
 	m_beeper->add_route(ALL_OUTPUTS, "mono", 0.25);
 }
 
@@ -256,13 +256,13 @@ void conchess_state::concply5(machine_config &config)
 	R65C02(config.replace(), m_maincpu, 11_MHz_XTAL/2);
 	m_maincpu->set_addrmap(AS_PROGRAM, &conchess_state::main_map);
 
-	const attotime irq_period = attotime::from_hz(11_MHz_XTAL/2 / 0x2000);
+	const attotime irq_period = attotime::from_hz(11_MHz_XTAL / 0x4000);
 	m_maincpu->set_periodic_int(FUNC(conchess_state::irq0_line_assert), irq_period);
 
 	SOFTWARE_LIST(config.replace(), "cart_list").set_original("conchess_plymate");
 
 	/* sound hardware */
-	BEEP(config.replace(), m_beeper, 11_MHz_XTAL/2 / 0x400);
+	BEEP(config.replace(), m_beeper, 11_MHz_XTAL / 0x800);
 	m_beeper->add_route(ALL_OUTPUTS, "mono", 0.25);
 }
 
@@ -274,11 +274,11 @@ void conchess_state::concply8(machine_config &config)
 	R65C02(config.replace(), m_maincpu, 16_MHz_XTAL/2);
 	m_maincpu->set_addrmap(AS_PROGRAM, &conchess_state::main_map);
 
-	const attotime irq_period = attotime::from_hz(16_MHz_XTAL/2 / 0x2000);
+	const attotime irq_period = attotime::from_hz(16_MHz_XTAL / 0x4000);
 	m_maincpu->set_periodic_int(FUNC(conchess_state::irq0_line_assert), irq_period);
 
 	/* sound hardware */
-	BEEP(config.replace(), m_beeper, 16_MHz_XTAL/2 / 0x800);
+	BEEP(config.replace(), m_beeper, 16_MHz_XTAL / 0x1000);
 	m_beeper->add_route(ALL_OUTPUTS, "mono", 0.25);
 }
 
@@ -290,13 +290,13 @@ void conchess_state::concplyv(machine_config &config)
 	M65C02(config.replace(), m_maincpu, 12.288_MHz_XTAL/2);
 	m_maincpu->set_addrmap(AS_PROGRAM, &conchess_state::main_map);
 
-	const attotime irq_period = attotime::from_hz(12.288_MHz_XTAL/2 / 0x2000);
+	const attotime irq_period = attotime::from_hz(12.288_MHz_XTAL / 0x4000);
 	m_maincpu->set_periodic_int(FUNC(conchess_state::irq0_line_assert), irq_period);
 
 	SOFTWARE_LIST(config.replace(), "cart_list").set_original("conchess_victoria");
 
 	/* sound hardware */
-	BEEP(config.replace(), m_beeper, 12.288_MHz_XTAL/2 / 0x800);
+	BEEP(config.replace(), m_beeper, 12.288_MHz_XTAL / 0x1000);
 	m_beeper->add_route(ALL_OUTPUTS, "mono", 0.25);
 }
 
diff --git a/src/mame/drivers/fidel_eag68k.cpp b/src/mame/drivers/fidel_eag68k.cpp
index 380d3d6a8bc..4ce43644894 100644
--- a/src/mame/drivers/fidel_eag68k.cpp
+++ b/src/mame/drivers/fidel_eag68k.cpp
@@ -472,7 +472,7 @@ void eagv5_state::main_map(address_map &map)
 void eagv5_state::sub_map(address_map &map)
 {
 	map(0x000000, 0x00ffff).rom();
-	map(0x000001, 0x000001).mirror(0x00fffe).w(m_sublatch, FUNC(generic_latch_8_device::write));
+	map(0x000000, 0x000001).mirror(0x00fffe).w(m_sublatch, FUNC(generic_latch_8_device::write)).umask16(0x00ff);
 	map(0x044000, 0x047fff).ram();
 	map(0x140000, 0x140000).r(FUNC(eagv5_state::sub_ack_r));
 	map(0x140001, 0x140001).r(m_mainlatch, FUNC(generic_latch_8_device::read));
diff --git a/src/mame/drivers/segac2.cpp b/src/mame/drivers/segac2.cpp
index 1be460ff039..112a4571dea 100644
--- a/src/mame/drivers/segac2.cpp
+++ b/src/mame/drivers/segac2.cpp
@@ -674,11 +674,11 @@ void pclub_state::print_club_camera_w(uint16_t data)
 void segac2_state::segac_map(address_map &map)
 {
 	map(0x000000, 0x1fffff).rom();
-	map(0x800001, 0x800001).mirror(0x13fdfe).rw(FUNC(segac2_state::prot_r), FUNC(segac2_state::prot_w));
-	map(0x800201, 0x800201).mirror(0x13fdfe).w(FUNC(segac2_state::control_w));
+	map(0x800000, 0x800001).mirror(0x13fdfe).rw(FUNC(segac2_state::prot_r), FUNC(segac2_state::prot_w)).umask16(0x00ff);
+	map(0x800200, 0x800201).mirror(0x13fdfe).w(FUNC(segac2_state::control_w)).umask16(0x00ff);
 	map(0x840000, 0x84001f).mirror(0x13fee0).rw("io", FUNC(sega_315_5296_device::read), FUNC(sega_315_5296_device::write)).umask16(0x00ff);
 	map(0x840100, 0x840107).mirror(0x13fef8).rw(m_ymsnd, FUNC(ym3438_device::read), FUNC(ym3438_device::write)).umask16(0x00ff);
-	map(0x880101, 0x880101).mirror(0x13fefe).w(FUNC(segac2_state::counter_timer_w));
+	map(0x880100, 0x880101).mirror(0x13fefe).w(FUNC(segac2_state::counter_timer_w)).umask16(0x00ff);
 	map(0x8c0000, 0x8c0fff).mirror(0x13f000).rw(FUNC(segac2_state::palette_r), FUNC(segac2_state::palette_w)).share("paletteram");
 	map(0xc00000, 0xc0001f).mirror(0x18ff00).rw(m_vdp, FUNC(sega315_5313_device::vdp_r), FUNC(sega315_5313_device::vdp_w));
 	map(0xe00000, 0xe0ffff).mirror(0x1f0000).ram().share("nvram");