m68k-backplane-computer/emu
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Fix offset to link being treated as unsigned

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This commit is contained in:
pjht 2023-11-07 14:56:30 -06:00
parent d361b5a090
commit a0ca311e9a
Signed by: pjht
GPG Key ID: CA239FC6934E6F3A
3 changed files with 10 additions and 5 deletions
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2
src/disas.rs
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@ -460,7 +460,7 @@ impl<T> Disasm<'_, T> {
Ok(Instruction::Trap(vector))
} else if ins_word[4..13].load_be::<u16>() == 0b1_1100_1010 {
let areg = ins_word[13..16].load_be::<u8>();
let displacement = self.read_immediate(Size::Word)? as u16;
let displacement = self.read_immediate(Size::Word)? as i16;
Ok(Instruction::Link {areg, displacement})
} else if ins_word[4..13].load_be::<u16>() == 0b1_1100_1011 {
let dst = ins_word[13..16].load_be::<u8>();

4
src/instruction.rs
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@ -334,7 +334,7 @@ pub enum Instruction {
Trap(u8),
Link {
areg: u8,
displacement: u16,
displacement: i16,
},
Unlk(u8),
MoveUsp(MoveDirection, u8),
@ -475,7 +475,7 @@ impl Display for Instruction {
Self::Tas(dst) => write!(f, "TAS {dst}"),
Self::Tst(size, src) => write!(f, "TST.{size} {src}"),
Self::Trap(vec) => write!(f, "TRAP #{vec:#x}"),
Self::Link { areg, displacement } => write!(f, "LINK A{areg}, #{displacement:#x}"),
Self::Link { areg, displacement } => write!(f, "LINK A{areg}, #{displacement}"),
Self::Unlk(areg) => write!(f, "UNLK A{areg}"),
Self::MoveUsp(dir, areg) => match dir {
MoveDirection::MemToReg => write!(f, "MOVE USP, A{areg}"),

7
src/m68k.rs
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@ -595,9 +595,14 @@ impl M68K {
self.push(dst_val, Size::Long)?;
let sp = self.read_effective(EffectiveAddress::AddressReg(7), Size::Long)?;
self.write_effective(dst, sp, Size::Long)?;
let new_sp = if displacement >= 0 {
sp.wrapping_add(displacement as u32)
} else {
sp.wrapping_sub(-displacement as u32)
};
self.write_effective(
EffectiveAddress::AddressReg(7),
sp.wrapping_add(u32::from(displacement)),
new_sp,
Size::Long,
)?;
}