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removed read8BitZeroPage() from cpu implementation

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this was a leftover from previous implementation of the memory system.
it's no longer required
This commit is contained in:
JetSetIlly 2023-02-17 19:05:57 +00:00
parent 6fa1f42118
commit 290b2c8500
1 changed files with 2 additions and 44 deletions
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46
hardware/cpu/cpu.go
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@ -225,31 +225,6 @@ func (mc *CPU) read8Bit(address uint16, phantom bool) (uint8, error) {
return val, nil
}
// read8BitZero returns 8bit value from the specified zero-page address
//
// side-effects:
// - calls cycleCallback after memory read
func (mc *CPU) read8BitZeroPage(address uint8) (uint8, error) {
mc.PhantomMemAccess = false
val, err := mc.mem.Read(uint16(address))
if err != nil {
if !errors.Is(err, cpubus.AddressError) {
return 0, err
}
mc.LastResult.Error = err.Error()
}
// +1 cycle
mc.LastResult.Cycles++
err = mc.cycleCallback()
if err != nil {
return 0, err
}
return val, nil
}
// write8Bit writes 8 bits to the specified address. there are no side effects
// on the state of the CPU which means that *cycleCallback must be called by the
// calling function as appropriate*.
@ -591,9 +566,6 @@ func (mc *CPU) ExecuteInstruction(cycleCallback func() error) error {
// change during execution and be used to write back to memory
var value uint8
// whether the data-read should be a zero page read or not
var zeroPage bool
// sometimes the CPU may be reset mid-instruction. if this happens
// LastResult.Defn will be nil. there's nothing we can do except return
// immediately
@ -670,8 +642,6 @@ func (mc *CPU) ExecuteInstruction(cycleCallback func() error) error {
// this part of the operation to the operator switch below
case instructions.ZeroPage:
zeroPage = true
// +1 cycle
//
// while we must trest the value as an address (ie. as uint16) we
@ -872,8 +842,6 @@ func (mc *CPU) ExecuteInstruction(cycleCallback func() error) error {
address = mc.acc16.Address()
case instructions.ZeroPageIndexedX:
zeroPage = true
// +1 cycles
err = mc.read8BitPC(loNibble)
if err != nil {
@ -898,8 +866,6 @@ func (mc *CPU) ExecuteInstruction(cycleCallback func() error) error {
}
case instructions.ZeroPageIndexedY:
zeroPage = true
// used exclusively for LDX ZeroPage,y
// +1 cycles
@ -939,21 +905,13 @@ func (mc *CPU) ExecuteInstruction(cycleCallback func() error) error {
if !(defn.AddressingMode == instructions.Implied || defn.AddressingMode == instructions.Immediate) {
if defn.Effect == instructions.Read {
// +1 cycle
if zeroPage {
value, err = mc.read8BitZeroPage(uint8(address))
} else {
value, err = mc.read8Bit(address, false)
}
value, err = mc.read8Bit(address, false)
if err != nil {
return err
}
} else if defn.Effect == instructions.RMW {
// +1 cycle
if zeroPage {
value, err = mc.read8BitZeroPage(uint8(address))
} else {
value, err = mc.read8Bit(address, false)
}
value, err = mc.read8Bit(address, false)
if err != nil {
return err
}