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https://github.com/JetSetIlly/Gopher2600.git
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4c530bf7a7
- 6502 implementation is basically correct but does not handle
- interrupts
- pre-fetch cycle
- anything less fine grained than instruction stepping
- memory sub-system sketched in
o retroactive adding of GPL copyright notice
98 lines
1.5 KiB
Go
98 lines
1.5 KiB
Go
package cpu
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// StatusRegister is the special purpose register that stores the flags of the CPU
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type StatusRegister struct {
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Sign bool
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Overflow bool
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Break bool
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DecimalMode bool
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InterruptDisable bool
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Zero bool
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Carry bool
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}
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func (sr StatusRegister) String() string {
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var v string
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if sr.Sign {
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v += "S"
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} else {
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v += "s"
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}
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if sr.Overflow {
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v += "V"
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} else {
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v += "v"
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}
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v += "-"
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if sr.Break {
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v += "B"
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} else {
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v += "b"
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}
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if sr.DecimalMode {
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v += "D"
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} else {
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v += "d"
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}
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if sr.InterruptDisable {
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v += "I"
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} else {
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v += "i"
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}
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if sr.Zero {
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v += "Z"
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} else {
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v += "z"
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}
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if sr.Carry {
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v += "C"
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} else {
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v += "c"
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}
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return v
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}
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// ToUint8 converts the StatusRegister struct into a value suitable for pushing
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// onto the stack
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func (sr *StatusRegister) ToUint8() uint8 {
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var v uint8
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if sr.Sign {
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v |= 0x80
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}
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if sr.Overflow {
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v |= 0x40
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}
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if sr.Break {
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v |= 0x10
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}
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if sr.DecimalMode {
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v |= 0x08
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}
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if sr.InterruptDisable {
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v |= 0x04
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}
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if sr.Zero {
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v |= 0x02
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}
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if sr.Carry {
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v |= 0x01
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}
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return v
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}
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// FromUint8 converts an 8 bit integer (taken from the stack, for example) to
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// the StatusRegister struct receiver
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func (sr *StatusRegister) FromUint8(v uint8) {
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sr.Sign = v&0x80 == 0x80
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sr.Overflow = v&0x40 == 0x40
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sr.Break = v&0x10 == 0x10
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sr.DecimalMode = v&0x08 == 0x08
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sr.InterruptDisable = v&0x04 == 0x04
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sr.Zero = v&0x02 == 0x02
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sr.Carry = v&0x01 == 0x01
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}
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