RomCrossBlaim.cc

Go to the documentation of this file.

// Thanks to hap (enen) for buying the real cartridge and
// investigating it in detail. See his results on:
//
//   http://www.msx.org/forumtopicl8629.html
//
// To summarize:
//   The whole 0x0000-0xffff region acts as a single switch region. Only
//   the lower 2 bits of the written value have any effect. The mapping
//   is like the table below. The initial state is 00.
//
//                    | 0x | 10 | 11
//      --------------+----+----+----
//      0x0000-0x3fff |  1 |  x |  x    (x means unmapped, reads as 0xff)
//      0x4000-0x7fff |  0 |  0 |  0
//      0x8000-0xbfff |  1 |  2 |  3
//      0xc000-0xffff |  1 |  x |  x
 
#include "RomCrossBlaim.hh"
#include "serialize.hh"
 
namespace openmsx {
 
RomCrossBlaim::RomCrossBlaim(const DeviceConfig& config, Rom&& rom_)
        : Rom16kBBlocks(config, std::move(rom_))
{
        reset(EmuTime::dummy());
}
 
void RomCrossBlaim::reset(EmuTime::param time)
{
        writeMem(0, 0, time);
}
 
void RomCrossBlaim::writeMem(word /*address*/, byte value, EmuTime::param /*time*/)
{
        switch (value & 3) {
                case 0:
                case 1:
                        setRom(0, 1);
                        setRom(1, 0);
                        setRom(2, 1);
                        setRom(3, 1);
                        break;
                case 2:
                        setUnmapped(0);
                        setRom(1, 0);
                        setRom(2, 2);
                        setUnmapped(3);
                        break;
                case 3:
                        setUnmapped(0);
                        setRom(1, 0);
                        setRom(2, 3);
                        setUnmapped(3);
                        break;
        }
}
 
byte* RomCrossBlaim::getWriteCacheLine(word /*address*/)
{
        return nullptr;
}
 
REGISTER_MSXDEVICE(RomCrossBlaim, "RomCrossBlaim");
 
} // namespace openmsx