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https://github.com/bradford-hamilton/apple-1.git
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366b4ce53e
Create some data structures to start building the CPU. Outside of some new structures, the majority of the work in this CL was adding all apple1 opcodes.
59 lines
2.5 KiB
Go
59 lines
2.5 KiB
Go
package cpu
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// A .... Accumulator OPC A operand is AC (implied single byte instruction)
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// abs .... absolute OPC $LLHH operand is address $HHLL *
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// abs,X .... absolute, X-indexed OPC $LLHH,X operand is address; effective address is address incremented by X with carry **
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// abs,Y .... absolute, Y-indexed OPC $LLHH,Y operand is address; effective address is address incremented by Y with carry **
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// # .... immediate OPC #$BB operand is byte BB
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// impl .... implied OPC operand implied
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// ind .... indirect OPC ($LLHH) operand is address; effective address is contents of word at address: C.w($HHLL)
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// X,ind .... X-indexed, indirect OPC ($LL,X) operand is zeropage address; effective address is word in (LL + X, LL + X + 1), inc. without carry: C.w($00LL + X)
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// ind,Y .... indirect, Y-indexed OPC ($LL),Y operand is zeropage address; effective address is word in (LL, LL + 1) incremented by Y with carry: C.w($00LL) + Y
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// rel .... relative OPC $BB branch target is PC + signed offset BB ***
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// zpg .... zeropage OPC $LL operand is zeropage address (hi-byte is zero, address = $00LL)
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// zpg,X .... zeropage, X-indexed OPC $LL,X operand is zeropage address; effective address is address incremented by X without carry **
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// zpg,Y .... zeropage, Y-indexed OPC $LL,Y operand is zeropage address; effective address is address incremented by Y without carry **
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// 16-bit address words are little endian, lo(w)-byte first, followed by the hi(gh)-byte.
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// SR Flags (bit 7 to bit 0):
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// N .... Negative
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// V .... Overflow
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// - .... ignored
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// B .... Break
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// D .... Decimal (use BCD for arithmetics)
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// I .... Interrupt (IRQ disable)
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// Z .... Zero
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// C .... Carry
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// Processor Stack:
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// LIFO, top down, 8 bit range, 0x0100 - 0x01FF
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// addressingMode is a type alias for a string, used below for defining addressing mode types
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type addressingMode int
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const (
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accumulator addressingMode = iota
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absolute
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absoluteXIndexed
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absoluteYIndexed
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immediate
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implied
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indirect
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indirectXIndexed
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indirectYIndexed
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relative
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zeroPage
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zeroPageXIndexed
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zeroPageYIndexed
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)
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type mos6502cpu struct {
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pc uint16 // program counter (16 bit)
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ac uint8 // accumulator (8 bit)
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x uint8 // X register (8 bit)
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y uint8 // Y register (8 bit)
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sr uint8 // status register [NV-BDIZC] (8 bit)
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sp uint8 // stack pointer (8 bit)
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}
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