mbc.c

#include "mbc.h"
#include "mem.h"
#include "rom.h"
 
enum {
    NO_FILTER_WRITE,
    FILTER_WRITE
};
 
static unsigned int bank_upper_bits;
static unsigned int ram_select;
 
/* Unfinished, no clock etc */
unsigned int MBC3_write_byte(unsigned short d, unsigned char i)
{
    int bank;
 
    if(d < 0x2000)
    {
        return FILTER_WRITE;
    }
 
    if(d < 0x4000)
    {
        bank = i & 0x7F;
 
        if(bank == 0)
            bank++;
 
        mem_bank_switch(bank);
 
        return FILTER_WRITE;
    }
 
    if(d < 0x8000)
        return FILTER_WRITE;
 
    return NO_FILTER_WRITE;
}
unsigned int MBC1_write_byte(unsigned short d, unsigned char i)
{
    int bank;
 
    if(d < 0x2000)
    {
        return FILTER_WRITE;
        /* TODO: Enable/disable SRAM */
    }
 
    /* Switch rom bank at 4000-7fff */
    if(d >= 0x2000 && d < 0x4000)
    {
        /* Bits 0-4 come from the value written to memory here,
         * bits 5-6 come from a seperate write to 4000-5fff if
         * RAM select is 1.
         */
        bank = i & 0x1F;
        if(!ram_select)
            bank |= bank_upper_bits;
 
        /* "Writing to this address space selects the lower 5 bits of the
         * ROM Bank Number (in range 01-1Fh). When 00h is written, the MBC
         * translates that to bank 01h also."
         * http://nocash.emubase.de/pandocs.htm#mbc1max2mbyteromandor32kbyteram
         */
 
        if(bank == 0 || bank == 0x20 || bank == 0x40 || bank == 0x60)
            bank++;
 
        mem_bank_switch(bank);
 
        return FILTER_WRITE;
    }
 
    /* Bit 5 and 6 of the bank selection */
    if(d >= 0x4000 && d < 0x6000)
    {
        bank_upper_bits = (i & 0x3)<<5;
        return FILTER_WRITE;
    }
 
    if(d >= 0x6000 && d <= 0x7FFF)
    {
        ram_select = i&1;
        return FILTER_WRITE;
    }
    return NO_FILTER_WRITE;
}