diff --git a/src/devices/bus/gameboy/cartbase.ipp b/src/devices/bus/gameboy/cartbase.ipp
index 39bde1c857f..eb10795591e 100644
--- a/src/devices/bus/gameboy/cartbase.ipp
+++ b/src/devices/bus/gameboy/cartbase.ipp
@@ -77,7 +77,6 @@ void flat_ram_device_base<Base>::install_ram()
 				nvrambytes,
 				0x1fff,
 				0,
-				0,
 				0xa000,
 				[this, nvrambase] (offs_t begin, offs_t end, offs_t mirror, offs_t src)
 				{
@@ -111,7 +110,6 @@ void flat_ram_device_base<Base>::install_ram()
 					rambytes,
 					0x1fff,
 					0,
-					0,
 					0xa000,
 					[this, rambase] (offs_t begin, offs_t end, offs_t mirror, offs_t src)
 					{
@@ -131,7 +129,6 @@ void flat_ram_device_base<Base>::install_ram()
 					rambytes,
 					nvrambytes - 1,
 					0,
-					0,
 					0xa000 | nvrambytes,
 					[this, rambase, highmirror = 0x1fff & ~(nvrambytes | (nvrambytes - 1))] (offs_t begin, offs_t end, offs_t mirror, offs_t src)
 					{
@@ -353,7 +350,6 @@ void mbc_ram_device_base<Base>::install_ram(
 				nvrambytes ? nvrambytes : rambytes,
 				PAGE_RAM_SIZE - 1,
 				0,
-				0,
 				0xa000,
 				[this, rospace, rwspace, base = nvrambase ? nvrambase : rambase] (offs_t begin, offs_t end, offs_t mirror, offs_t src)
 				{
diff --git a/src/devices/bus/gameboy/mbc6.cpp b/src/devices/bus/gameboy/mbc6.cpp
index 66551678200..322619dd9d6 100644
--- a/src/devices/bus/gameboy/mbc6.cpp
+++ b/src/devices/bus/gameboy/mbc6.cpp
@@ -479,7 +479,6 @@ void mbc6_device::install_ram()
 				nvrambytes ? nvrambytes : rambytes,
 				PAGE_RAM_SIZE - 1,
 				0,
-				0,
 				0xa000,
 				[this, base = nvrambase ? nvrambase : rambase] (offs_t begin, offs_t end, offs_t mirror, offs_t src)
 				{
diff --git a/src/devices/bus/gameboy/rom.cpp b/src/devices/bus/gameboy/rom.cpp
index c3dfeeb68bb..e2bb928524f 100644
--- a/src/devices/bus/gameboy/rom.cpp
+++ b/src/devices/bus/gameboy/rom.cpp
@@ -330,7 +330,6 @@ public:
 				bytes,
 				0x7fff,
 				0,
-				0,
 				0x0000,
 				[this, base = &romregion->as_u8()] (offs_t begin, offs_t end, offs_t mirror, offs_t src)
 				{
diff --git a/src/devices/bus/generic/slot.h b/src/devices/bus/generic/slot.h
index 9fde07ddd83..2e2a99a50b5 100644
--- a/src/devices/bus/generic/slot.h
+++ b/src/devices/bus/generic/slot.h
@@ -63,6 +63,33 @@ public:
 		}
 	}
 
+	// TODO: find a better home for this helper
+	template <unsigned Shift, typename T>
+	static void install_non_power_of_two(
+			offs_t length,
+			offs_t decode_limit,
+			offs_t decode_offset,
+			offs_t base,
+			T &&install)
+	{
+		offs_t decode_mask(length - 1);
+		for (unsigned i = 31 - count_leading_zeros_32(decode_mask); 0U < i; --i)
+		{
+			if (!BIT(decode_mask, i - 1))
+			{
+				decode_mask &= ~((offs_t(1) << i) - 1);
+				break;
+			}
+		}
+		install_non_power_of_two<Shift, T>(
+				length,
+				decode_limit,
+				decode_mask,
+				decode_offset,
+				base,
+				std::forward<T>(install));
+	}
+
 	// TODO: find a better home for this helper
 	template <typename T, typename U>
 	static T map_non_power_of_two(T count, U &&map)
@@ -72,7 +99,7 @@ public:
 
 		T const max(count - 1);
 		T mask(max);
-		for (unsigned i = 1; (sizeof(T) * 8) > i; i <<= 1)
+		for (unsigned i = 1U; (sizeof(T) * 8) > i; i <<= 1)
 			mask = T(std::make_unsigned_t<T>(mask) | (std::make_unsigned_t<T>(mask) >> i));
 		int bits(0);
 		while (BIT(mask, bits))
diff --git a/src/devices/bus/vboy/rom.cpp b/src/devices/bus/vboy/rom.cpp
index 65724108b41..20ba18ff62a 100644
--- a/src/devices/bus/vboy/rom.cpp
+++ b/src/devices/bus/vboy/rom.cpp
@@ -62,7 +62,6 @@ std::error_condition vboy_flat_rom_device::load()
 				romregion->bytes() >> 2,
 				0x00ff'ffff >> 2,
 				0,
-				0,
 				rom_base(),
 				[this, rom = &romregion->as_u32()] (offs_t begin, offs_t end, offs_t mirror, offs_t src)
 				{
@@ -118,7 +117,6 @@ std::error_condition vboy_flat_rom_sram_device::load()
 						sramregion->bytes() >> 1,
 						0x00ff'ffff >> 2,
 						0,
-						0,
 						chip_base(),
 						[this, sramregion] (offs_t begin, offs_t end, offs_t mirror, offs_t src)
 						{
@@ -151,7 +149,6 @@ std::error_condition vboy_flat_rom_sram_device::load()
 						sramregion->bytes() >> 2,
 						0x00ff'ffff >> 2,
 						0,
-						0,
 						chip_base(),
 						[this, sramregion] (offs_t begin, offs_t end, offs_t mirror, offs_t src)
 						{