[WIP] Gamepak unused addresses

Former-commit-id: 7946d38faf49fc0f95aab8654611b94aae443949
Former-commit-id: b3654fd4750d472a20fe5db9de0019d774a4ee61
This commit is contained in:
Michel Heily 2020-05-30 13:12:12 +03:00
parent e14c5996d4
commit 130a7608e7

View file

@ -82,6 +82,20 @@ impl Cartridge {
self.symbols = other.symbols; self.symbols = other.symbols;
self.backup = other.backup; self.backup = other.backup;
} }
#[inline]
/// From GBATEK:
/// Reading from GamePak ROM when no Cartridge is inserted -
/// Because Gamepak uses the same signal-lines for both 16bit data and for lower 16bit halfword address,
/// the entire gamepak ROM area is effectively filled by incrementing 16bit values (Address/2 AND FFFFh).
fn read_unused(&self, addr: Addr) -> u8 {
let x = (addr / 2) & 0xffff;
if addr & 1 != 0 {
(x >> 8) as u8
} else {
x as u8
}
}
} }
use super::sysbus::consts::*; use super::sysbus::consts::*;
@ -106,7 +120,7 @@ impl Bus for Cartridge {
}, },
_ => { _ => {
if offset >= self.size { if offset >= self.size {
0xDD // TODO - open bus implementation self.read_unused(addr)
} else { } else {
unsafe { *self.bytes.get_unchecked(offset as usize) } unsafe { *self.bytes.get_unchecked(offset as usize) }
} }
@ -167,6 +181,10 @@ impl Bus for Cartridge {
impl DebugRead for Cartridge { impl DebugRead for Cartridge {
fn debug_read_8(&mut self, addr: Addr) -> u8 { fn debug_read_8(&mut self, addr: Addr) -> u8 {
let offset = (addr & 0x01ff_ffff) as usize; let offset = (addr & 0x01ff_ffff) as usize;
if offset >= self.size {
self.read_unused(addr)
} else {
self.bytes[offset] self.bytes[offset]
} }
} }
}