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Add EXG instruction to the 6809

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Signed-off-by: Adrian Conlon <Adrian.conlon@gmail.com>
This commit is contained in:
Adrian Conlon 2018-08-21 14:51:56 +01:00
parent f1f64dad93
commit 8c8c02f4b7
3 changed files with 60 additions and 0 deletions
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7
MC6809/inc/mc6809.h
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@ -96,6 +96,12 @@ namespace EightBit {
// Register selection for "indexed"
register16_t& RR(int which);
// Register selection for 8-bit transfer/exchange
uint8_t& referenceTransfer8(int specifier);
// Register selection for 16-bit transfer/exchange
register16_t& referenceTransfer16(int specifier);
// Addressing modes
void Address_direct(); // DP + fetched offset
@ -188,6 +194,7 @@ namespace EightBit {
uint8_t da(uint8_t operand);
uint8_t dec(uint8_t operand);
uint8_t eor(uint8_t operand, uint8_t data);
void exg(uint8_t data);
uint8_t neg(uint8_t operand);
register16_t m_d;

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MC6809/inc/stdafx.h
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53
MC6809/src/mc6809.cpp
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@ -1,6 +1,8 @@
#include "stdafx.h"
#include "mc6809.h"
#include <algorithm>
EightBit::mc6809::mc6809(Bus& bus)
: BigEndianProcessor(bus) {}
@ -182,6 +184,9 @@ int EightBit::mc6809::executeUnprefixed(uint8_t opcode) {
case 0xe8: addCycles(4); B() = eor(B(), AM_indexed_byte()); break; // EOR (EORB indexed)
case 0xf8: addCycles(5); B() = eor(B(), AM_extended_byte()); break; // EOR (EORB extended)
// EXG
case 0x1e: addCycles(8); exg(AM_immediate_byte()); break; // EXG (EXG R1,R2 immediate)
default:
UNREACHABLE;
}
@ -519,3 +524,51 @@ uint8_t EightBit::mc6809::eor(uint8_t operand, uint8_t data) {
clearFlag(CC(), VF);
return result;
}
uint8_t& EightBit::mc6809::referenceTransfer8(int specifier) {
switch (specifier) {
case 0b1000:
return A();
case 0b1001:
return B();
case 0b1010:
return CC();
case 0b1011:
return DP();
default:
UNREACHABLE;
}
}
EightBit::register16_t& EightBit::mc6809::referenceTransfer16(int specifier) {
switch (specifier) {
case 0b0000:
return D();
case 0b0001:
return X();
case 0b0010:
return Y();
case 0b0011:
return U();
case 0b0100:
return S();
case 0b0101:
return PC();
default:
UNREACHABLE;
}
}
void EightBit::mc6809::exg(uint8_t data) {
const auto reg1 = highNibble(data);
const auto reg2 = lowNibble(data);
const bool type16 = !!(reg1 & Bit3); // 16 bit exchange?
ASSUME(type16 == !!(reg2 & Bit3)); // Regardless, the register exchange must be equivalent
if (type16)
std::swap(referenceTransfer16(reg1), referenceTransfer16(reg2));
else
std::swap(referenceTransfer8(reg1), referenceTransfer8(reg2));
}