/// <summary>
/// Handles the read from the port
/// </summary>
/// <param name="addr">Full port address</param>
/// <param name="readValue">The value read from the port</param>
/// <returns>True, if read handled; otherwise, false</returns>
public override bool HandleRead(ushort addr, out byte readValue)
{
readValue = _keyboardDevice.GetLineStatus((byte)(addr >> 8));
if (_tapeDevice.IsInLoadMode)
{
var earBit = _tapeDevice.GetEarBit(_cpu.Tacts);
if (!earBit)
{
readValue = (byte)(readValue & 0b1011_1111);
}
}
else
{
var bit4Sensed = _bit4LastValue;
if (!bit4Sensed)
{
var chargeTime = _bit4ChangedFrom1 - _bit4ChangedFrom0;
if (chargeTime > 0)
{
var delay = Math.Min(chargeTime * 4, 2800);
bit4Sensed = _cpu.Tacts - _bit4ChangedFrom1 < delay;
}
}
var bit6Value = (_bit3LastValue || bit4Sensed) ? 0b0100_0000 : 0x00;
if (_bit3LastValue && !bit4Sensed && _isUla3)
{
bit6Value = 0x00;
}
readValue = (byte)((readValue & 0b1011_1111) | bit6Value);
}
return(true);
}
/// <summary>
/// Handles the read from the port
/// </summary>
/// <param name="addr">Full port address</param>
/// <param name="readValue">The value read from the port</param>
/// <returns>True, if read handled; otherwise, false</returns>
public override bool HandleRead(ushort addr, out byte readValue)
{
readValue = _keyboardDevice.GetLineStatus((byte)(addr >> 8));
var earBit = _tapeDevice.GetEarBit(_cpu.Tacts);
if (!earBit)
{
readValue = (byte)(readValue & 0b1011_1111);
}
return(true);
}
/// <summary>
/// Reads the port with the specified address
/// </summary>
/// <param name="addr">Port address</param>
/// <returns>Byte read from the port</returns>
public byte OnReadPort(ushort addr)
{
if ((addr & 0x0001) != 0)
{
return(0xFF);
}
var portBits = _keyboardDevice.GetLineStatus((byte)(addr >> 8));
var earBit = _tapeDevice.GetEarBit(_cpu.Tacts);
if (!earBit)
{
portBits = (byte)(portBits & 0b1011_1111);
}
return(portBits);
}
/// <summary>
/// Reads the port with the specified address
/// </summary>
/// <param name="addr">Port address</param>
/// <returns>Byte read from the port</returns>
public override byte OnReadPort(ushort addr)
{
// --- Handle I/O contention
ContentionWait(addr);
// --- Carry out I/O read operation
if ((addr & 0x0001) != 0)
{
return(0xFF);
}
var portBits = _keyboardDevice.GetLineStatus((byte)(addr >> 8));
var earBit = _tapeDevice.GetEarBit(Cpu.Tacts);
if (!earBit)
{
portBits = (byte)(portBits & 0b1011_1111);
}
return(portBits);
}