--- a/sega_mapper.c	Fri Dec 31 13:03:21 2021 -0800
+++ b/sega_mapper.c	Sat Jan 01 18:54:46 2022 -0800
@@ -1,4 +1,5 @@
 #include "genesis.h"
+#include "util.h"
 
 uint16_t read_sram_w(uint32_t address, m68k_context * context)
 {
@@ -43,6 +44,14 @@
 m68k_context * write_sram_area_w(uint32_t address, m68k_context * context, uint16_t value)
 {
 	genesis_context * gen = context->system;
+	if (gen->mapper_type == MAPPER_SEGA_MED_V2) {
+		if (gen->bank_regs[8] & 0x20) {
+			uint32_t bank = address >> 19;
+			address &= 0x7FFFF;
+			context->mem_pointers[gen->mapper_start_index + bank][address >> 1] = value;
+		}
+		return context;
+	}
 	if ((gen->bank_regs[0] & 0x3) == 1) {
 		address &= gen->save_ram_mask;
 		switch(gen->save_type)
@@ -87,14 +96,128 @@
 	return context;
 }
 
+static void* write_med_ram_w(uint32_t address, void *vcontext, uint16_t value, uint16_t bank)
+{
+	m68k_context *context = vcontext;
+	genesis_context * gen = context->system;
+	if (gen->bank_regs[8] & 0x20) {
+		context->mem_pointers[gen->mapper_start_index + bank][address >> 1] = value;
+		address += bank * 0x80000;
+		m68k_invalidate_code_range(gen->m68k, address, address + 2);
+	}
+	return vcontext;
+}
+
+void* write_med_ram0_w(uint32_t address, void *vcontext, uint16_t value)
+{
+	return write_med_ram_w(address, vcontext, value, 0);
+}
+
+void* write_med_ram1_w(uint32_t address, void *vcontext, uint16_t value)
+{
+	return write_med_ram_w(address, vcontext, value, 1);
+}
+
+void* write_med_ram2_w(uint32_t address, void *vcontext, uint16_t value)
+{
+	return write_med_ram_w(address, vcontext, value, 2);
+}
+
+void* write_med_ram3_w(uint32_t address, void *vcontext, uint16_t value)
+{
+	return write_med_ram_w(address, vcontext, value, 3);
+}
+
+void* write_med_ram4_w(uint32_t address, void *vcontext, uint16_t value)
+{
+	return write_med_ram_w(address, vcontext, value, 4);
+}
+
+void* write_med_ram5_w(uint32_t address, void *vcontext, uint16_t value)
+{
+	return write_med_ram_w(address, vcontext, value, 5);
+}
+
+void* write_med_ram6_w(uint32_t address, void *vcontext, uint16_t value)
+{
+	return write_med_ram_w(address, vcontext, value, 6);
+}
+
+void* write_med_ram7_w(uint32_t address, void *vcontext, uint16_t value)
+{
+	return write_med_ram_w(address, vcontext, value, 7);
+}
+
+static void* write_med_ram_b(uint32_t address, void *vcontext, uint8_t value, uint16_t bank)
+{
+	m68k_context *context = vcontext;
+	genesis_context * gen = context->system;
+	if (gen->bank_regs[8] & 0x20) {
+		((uint8_t*)context->mem_pointers[gen->mapper_start_index + bank])[address ^ 1] = value;
+		address += bank * 0x80000;
+		m68k_invalidate_code_range(gen->m68k, address, address + 1);
+	}
+	return vcontext;
+}
+
+void* write_med_ram0_b(uint32_t address, void *vcontext, uint8_t value)
+{
+	return write_med_ram_b(address, vcontext, value, 0);
+}
+
+void* write_med_ram1_b(uint32_t address, void *vcontext, uint8_t value)
+{
+	return write_med_ram_b(address, vcontext, value, 1);
+}
+
+void* write_med_ram2_b(uint32_t address, void *vcontext, uint8_t value)
+{
+	return write_med_ram_b(address, vcontext, value, 2);
+}
+
+void* write_med_ram3_b(uint32_t address, void *vcontext, uint8_t value)
+{
+	return write_med_ram_b(address, vcontext, value, 3);
+}
+
+void* write_med_ram4_b(uint32_t address, void *vcontext, uint8_t value)
+{
+	return write_med_ram_b(address, vcontext, value, 4);
+}
+
+void* write_med_ram5_b(uint32_t address, void *vcontext, uint8_t value)
+{
+	return write_med_ram_b(address, vcontext, value, 5);
+}
+
+void* write_med_ram6_b(uint32_t address, void *vcontext, uint8_t value)
+{
+	return write_med_ram_b(address, vcontext, value, 6);
+}
+
+void* write_med_ram7_b(uint32_t address, void *vcontext, uint8_t value)
+{
+	return write_med_ram_b(address, vcontext, value, 7);
+}
+
 m68k_context * write_bank_reg_w(uint32_t address, m68k_context * context, uint16_t value)
 {
 	genesis_context * gen = context->system;
 	address &= 0xE;
 	address >>= 1;
-	gen->bank_regs[address] = value;
 	if (!address) {
-		if (value & 1) {
+		if (gen->mapper_type == MAPPER_SEGA_MED_V2) {
+			if (!value & 0x8000) {
+				//writes without protection bit set are ignored
+				return context;
+			}
+			gen->bank_regs[8] = value >> 8;
+			void *new_ptr = gen->cart + 0x40000*(value & 0x1F);
+			if (context->mem_pointers[gen->mapper_start_index] != new_ptr) {
+				m68k_invalidate_code_range(gen->m68k, 0, 0x80000);
+				context->mem_pointers[gen->mapper_start_index] = new_ptr;
+			}
+		} else if (value & 1) {
 			//Used for games that only use the mapper for SRAM
 			if (context->mem_pointers[gen->mapper_start_index]) {
 				gen->mapper_temp = context->mem_pointers[gen->mapper_start_index];
@@ -116,19 +239,30 @@
 				context->mem_pointers[gen->mapper_start_index + i] = gen->cart + 0x40000*gen->bank_regs[i];
 			}
 		}
-	} else if (gen->mapper_type == MAPPER_SEGA) {
-		void *new_ptr = gen->cart + 0x40000*value;
+	} else if (gen->mapper_type != MAPPER_SEGA_SRAM) {
+		uint32_t mask = ((gen->mapper_type == MAPPER_SEGA_MED_V2 ? (16 *1024 * 1024) : nearest_pow2(gen->header.info.rom_size)) >> 1) - 1;
+		void *new_ptr = gen->cart + ((0x40000*value) & mask);
 		if (context->mem_pointers[gen->mapper_start_index + address] != new_ptr) {
 			m68k_invalidate_code_range(gen->m68k, address * 0x80000, (address + 1) * 0x80000);
 			context->mem_pointers[gen->mapper_start_index + address] = new_ptr;
 		}
 	}
+	gen->bank_regs[address] = value;
 	return context;
 }
 
 m68k_context * write_bank_reg_b(uint32_t address, m68k_context * context, uint8_t value)
 {
-	if (address & 1) {
+	genesis_context * gen = context->system;
+	if (gen->mapper_type == MAPPER_SEGA_MED_V2) {
+		address &= 0xF;
+		if (!address) {
+			//not sure if this is correct, possible byte sized writes are always rejected to $A130F0
+			write_bank_reg_w(address, context, value << 8 | value);
+		} else if (address > 2 && (address & 1)) {
+			write_bank_reg_w(address, context, value);
+		}
+	} else if (address & 1) {
 		write_bank_reg_w(address, context, value);
 	}
 	return context;
@@ -136,13 +270,23 @@
 
 void sega_mapper_serialize(genesis_context *gen, serialize_buffer *buf)
 {
-	save_buffer8(buf, gen->bank_regs, sizeof(gen->bank_regs));
+	save_buffer8(buf, gen->bank_regs, gen->mapper_type == MAPPER_SEGA_MED_V2 ? sizeof(gen->bank_regs) : sizeof(gen->bank_regs) - 1);
 }
 
 void sega_mapper_deserialize(deserialize_buffer *buf, genesis_context *gen)
 {
-	for (int i = 0; i < sizeof(gen->bank_regs); i++)
-	{
-		write_bank_reg_w(i * 2, gen->m68k, load_int8(buf));
+	if (gen->mapper_type == MAPPER_SEGA_MED_V2) {
+		uint16_t reg0 = load_int8(buf);
+		for (int i = 1; i < sizeof(gen->bank_regs) - 1; i++)
+		{
+			write_bank_reg_w(i * 2, gen->m68k, load_int8(buf));
+		}
+		reg0 |= load_int8(buf) << 8;
+		write_bank_reg_w(0, gen->m68k, reg0);
+	} else {
+		for (int i = 0; i < sizeof(gen->bank_regs) - 1; i++)
+		{
+			write_bank_reg_w(i * 2, gen->m68k, load_int8(buf));
+		}
 	}
 }