mirror of https://github.com/ariejan/i6502.git
58 lines
1.3 KiB
Go
58 lines
1.3 KiB
Go
package cpu
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import (
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"fmt"
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"github.com/ariejan/i6502/bus"
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)
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// Instruction is a self-contained, variable length instruction,
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// it includes the the operation type and a possible 8 or 16 bit operand.
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type Instruction struct {
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OpType
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// 2 byte instructions have a single byte operand
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Op8 uint8
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// 3 byte instruction have a double byte operand
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Op16 uint16
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}
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func (i *Instruction) String() string {
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var output string
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switch i.Bytes {
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case 1:
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output = fmt.Sprintf("0x%02X - %s\n", i.Opcode, instructionNames[i.id])
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case 2:
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output = fmt.Sprintf("0x%02X - %s %02X\n", i.Opcode, instructionNames[i.id], i.Op8)
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case 3:
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output = fmt.Sprintf("0x%02X - %s %04X\n", i.Opcode, instructionNames[i.id], i.Op16)
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}
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return output
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}
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func ReadInstruction(pc uint16, bus *bus.Bus) Instruction {
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// Read the opcode
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opcode := bus.Read(pc)
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// Do we know this opcode in our optypes table?
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optype, ok := optypes[opcode]
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if !ok {
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panic(fmt.Sprintf("Unknown opcode $%02X at $%04X", opcode, pc))
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}
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instruction := Instruction{OpType: optype}
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switch instruction.Bytes {
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case 1: // No operand.
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case 2:
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instruction.Op8 = bus.Read(pc + 1)
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case 3:
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instruction.Op16 = bus.Read16(pc + 1)
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default:
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panic(fmt.Sprintf("Unknown instruction length (%d) for $%02X at $04X", instruction.Bytes, opcode, pc))
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}
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return instruction
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}
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