mbc.cpp

#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;
}