--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/sega_mapper.c	Fri Jun 23 23:16:44 2017 -0700
@@ -0,0 +1,135 @@
+#include "genesis.h"
+
+uint16_t read_sram_w(uint32_t address, m68k_context * context)
+{
+	genesis_context * gen = context->system;
+	address &= gen->save_ram_mask;
+	switch(gen->save_type)
+	{
+	case RAM_FLAG_BOTH:
+		return gen->save_storage[address] << 8 | gen->save_storage[address+1];
+	case RAM_FLAG_EVEN:
+		return gen->save_storage[address >> 1] << 8 | 0xFF;
+	case RAM_FLAG_ODD:
+		return gen->save_storage[address >> 1] | 0xFF00;
+	}
+	return 0xFFFF;//We should never get here
+}
+
+uint8_t read_sram_b(uint32_t address, m68k_context * context)
+{
+	genesis_context * gen = context->system;
+	address &= gen->save_ram_mask;
+	switch(gen->save_type)
+	{
+	case RAM_FLAG_BOTH:
+		return gen->save_storage[address];
+	case RAM_FLAG_EVEN:
+		if (address & 1) {
+			return 0xFF;
+		} else {
+			return gen->save_storage[address >> 1];
+		}
+	case RAM_FLAG_ODD:
+		if (address & 1) {
+			return gen->save_storage[address >> 1];
+		} else {
+			return 0xFF;
+		}
+	}
+	return 0xFF;//We should never get here
+}
+
+m68k_context * write_sram_area_w(uint32_t address, m68k_context * context, uint16_t value)
+{
+	genesis_context * gen = context->system;
+	if ((gen->bank_regs[0] & 0x3) == 1) {
+		address &= gen->save_ram_mask;
+		switch(gen->save_type)
+		{
+		case RAM_FLAG_BOTH:
+			gen->save_storage[address] = value >> 8;
+			gen->save_storage[address+1] = value;
+			break;
+		case RAM_FLAG_EVEN:
+			gen->save_storage[address >> 1] = value >> 8;
+			break;
+		case RAM_FLAG_ODD:
+			gen->save_storage[address >> 1] = value;
+			break;
+		}
+	}
+	return context;
+}
+
+m68k_context * write_sram_area_b(uint32_t address, m68k_context * context, uint8_t value)
+{
+	genesis_context * gen = context->system;
+	if ((gen->bank_regs[0] & 0x3) == 1) {
+		address &= gen->save_ram_mask;
+		switch(gen->save_type)
+		{
+		case RAM_FLAG_BOTH:
+			gen->save_storage[address] = value;
+			break;
+		case RAM_FLAG_EVEN:
+			if (!(address & 1)) {
+				gen->save_storage[address >> 1] = value;
+			}
+			break;
+		case RAM_FLAG_ODD:
+			if (address & 1) {
+				gen->save_storage[address >> 1] = value;
+			}
+			break;
+		}
+	}
+	return context;
+}
+
+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) {
+			//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];
+			}
+			context->mem_pointers[gen->mapper_start_index] = NULL;
+			//For games that need more than 4MB
+			for (int i = 4; i < 8; i++)
+			{
+				context->mem_pointers[gen->mapper_start_index + i] = NULL;
+			}
+		} else {
+			//Used for games that only use the mapper for SRAM
+			if (!context->mem_pointers[gen->mapper_start_index]) {
+				context->mem_pointers[gen->mapper_start_index] = gen->mapper_temp;
+			}
+			//For games that need more than 4MB
+			for (int i = 4; i < 8; i++)
+			{
+				context->mem_pointers[gen->mapper_start_index + i] = gen->cart + 0x40000*gen->bank_regs[i];
+			}
+		}
+	} else {
+		void *new_ptr = gen->cart + 0x40000*value;
+		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;
+		}
+	}
+	return context;
+}
+
+m68k_context * write_bank_reg_b(uint32_t address, m68k_context * context, uint8_t value)
+{
+	if (address & 1) {
+		write_bank_reg_w(address, context, value);
+	}
+	return context;
+}