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First stab at 6809 branching

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Signed-off-by: Adrian Conlon <Adrian.conlon@gmail.com>
This commit is contained in:
Adrian Conlon 2018-08-22 23:06:36 +01:00
parent 90fb124bd7
commit 4703b89a42
2 changed files with 84 additions and 3 deletions
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38
MC6809/inc/mc6809.h
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@ -134,9 +134,11 @@ namespace EightBit {
// Addressing modes
register16_t Address_direct(); // DP + fetched offset
register16_t Address_indexed(); // Indexed address, complicated!
register16_t Address_extended(); // Fetched address
register16_t Address_direct(); // DP + fetched offset
register16_t Address_indexed(); // Indexed address, complicated!
register16_t Address_extended(); // Fetched address
register16_t Address_relative_byte(); // PC + fetched byte offset
register16_t Address_relative_word(); // PC + fetched word offset
// Addressing mode readers
@ -222,6 +224,36 @@ namespace EightBit {
adjustSubtraction(before.word, data.word, after);
}
// Flag checking
int negative() { return CC() & NF; }
int zero() { return CC() & ZF; }
int overflow() { return CC() & VF; }
int carry() { return CC() & CF; }
bool BLS() { return carry() | (zero() >> 2); } // (C OR Z)
bool BHI() { return !BLS(); } // !(C OR Z)
bool BLT() { return (negative() >> 2) ^ overflow(); } // (N XOR V)
bool BGE() { return !BLT(); } // !(N XOR V)
bool BLE() { return (zero() >> 2) & ((negative() >> 3) ^ (overflow() >> 1)); } // (Z OR (N XOR V))
bool BGT() { return !BLE(); } // !(Z OR (N XOR V))
// Branching
bool branch(register16_t destination, int condition) {
if (condition)
jump(destination);
return !!condition;
}
bool branchShort(int condition) {
branch(Address_relative_byte(), condition);
}
bool branchLong(int condition) {
branch(Address_relative_word(), condition);
}
// Instruction implementations
uint8_t adc(uint8_t operand, uint8_t data);

49
MC6809/src/mc6809.cpp
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@ -300,6 +300,29 @@ int EightBit::mc6809::executeUnprefixed(uint8_t opcode) {
// RTS
case 0x39: addCycles(5); rts(); break; // RTS (RTS inherent)
// Branching
case 0x16: addCycles(5); jump(Address_relative_word()); break; // BRA (LBRA relative)
case 0x17: addCycles(9); call(Address_relative_word()); break; // BSR (LBSR relative)
case 0x20: addCycles(3); jump(Address_relative_byte()); break; // BRA (BRA relative)
case 0x21: addCycles(3); Address_relative_byte(); break; // BRN (BRN relative)
case 0x22: addCycles(3); branchShort(BHI()); break; // BHI (BHI relative)
case 0x23: addCycles(3); branchShort(BLS()); break; // BLS (BLS relative)
case 0x24: addCycles(3); branchShort(!carry()); break; // BCC (BCC relative)
case 0x25: addCycles(3); branchShort(carry()); break; // BCS (BCS relative)
case 0x26: addCycles(3); branchShort(!zero()); break; // BNE (BNE relative)
case 0x27: addCycles(3); branchShort(zero()); break; // BEQ (BEQ relative)
case 0x28: addCycles(3); branchShort(!overflow()); break; // BVC (BVC relative)
case 0x29: addCycles(3); branchShort(overflow()); break; // BVS (BVS relative)
case 0x2a: addCycles(3); branchShort(!negative()); break; // BPL (BPL relative)
case 0x2b: addCycles(3); branchShort(negative()); break; // BMI (BMI relative)
case 0x2c: addCycles(3); branchShort(BGE()); break; // BGE (BGE relative)
case 0x2d: addCycles(3); branchShort(BLT()); break; // BLT (BLT relative)
case 0x2e: addCycles(3); branchShort(BGT()); break; // BGT (BGT relative)
case 0x2f: addCycles(3); branchShort(BLE()); break; // BLE (BLE relative)
case 0x8d: addCycles(7); call(Address_relative_byte()); break; // BSR (BSR relative)
default:
UNREACHABLE;
}
@ -348,6 +371,24 @@ int EightBit::mc6809::execute10(uint8_t opcode) {
case 0xae: addCycles(6); Y() = ld(AM_indexed_word()); break; // LD (LDY indexed)
case 0xbe: addCycles(7); Y() = ld(AM_extended_word()); break; // LD (LDY extended)
// Branching
case 0x21: addCycles(5); Address_relative_word(); break; // BRN (LBRN relative)
case 0x22: addCycles(5); if (branchLong(BHI())) addCycle(); break; // BHI (LBHI relative)
case 0x23: addCycles(5); if (branchLong(BLS())) addCycle(); break; // BLS (LBLS relative)
case 0x24: addCycles(5); if (branchLong(!carry())) addCycle(); break; // BCC (LBCC relative)
case 0x25: addCycles(5); if (branchLong(carry())) addCycle(); break; // BCS (LBCS relative)
case 0x26: addCycles(5); if (branchLong(!zero())) addCycle(); break; // BNE (LBNE relative)
case 0x27: addCycles(5); if (branchLong(zero())) addCycle(); break; // BEQ (LBEQ relative)
case 0x28: addCycles(5); if (branchLong(!overflow())) addCycle();break; // BVC (LBVC relative)
case 0x29: addCycles(5); if (branchLong(overflow())) addCycle(); break; // BVS (LBVS relative)
case 0x2a: addCycles(5); if (branchLong(!negative())) addCycle();break; // BPL (LBPL relative)
case 0x2b: addCycles(5); if (branchLong(negative())) addCycle(); break; // BMI (LBMI relative)
case 0x2c: addCycles(5); if (branchLong(BGE())) addCycle(); break; // BGE (LBGE relative)
case 0x2d: addCycles(5); if (branchLong(BLT())) addCycle(); break; // BLT (LBLT relative)
case 0x2e: addCycles(5); if (branchLong(BGT())) addCycle(); break; // BGT (LBGT relative)
case 0x2f: addCycles(5); if (branchLong(BLE())) addCycle(); break; // BLE (LBLE relative)
default:
UNREACHABLE;
}
@ -419,6 +460,14 @@ EightBit::register16_t& EightBit::mc6809::RR(int which) {
}
}
EightBit::register16_t EightBit::mc6809::Address_relative_byte() {
return PC() + (int8_t)fetchByte();
}
EightBit::register16_t EightBit::mc6809::Address_relative_word() {
return PC() + (int16_t)fetchWord().word;
}
EightBit::register16_t EightBit::mc6809::Address_direct() {
return register16_t(fetchByte(), DP());
}