/// <summary>
/// Define how to handle an unattached port
/// </summary>
/// <param name="addr">Port address</param>
/// <returns>Port value for the unhandled port address</returns>
public override byte UnhandledRead(ushort addr)
{
var tact = HostVm.CurrentFrameTact % ScreenDevice.RenderingTactTable.Length;
var rt = ScreenDevice.RenderingTactTable[tact];
var memAddr = (ushort)0;
switch (rt.Phase)
{
case ScreenRenderingPhase.BorderFetchPixel:
case ScreenRenderingPhase.DisplayB1FetchB2:
case ScreenRenderingPhase.DisplayB2FetchB1:
memAddr = rt.PixelByteToFetchAddress;
break;
case ScreenRenderingPhase.BorderFetchPixelAttr:
case ScreenRenderingPhase.DisplayB1FetchA2:
case ScreenRenderingPhase.DisplayB2FetchA1:
memAddr = rt.AttributeToFetchAddress;
break;
}
if (memAddr == 0)
{
return(0xFF);
}
var readValue = _memoryDevice.Read(memAddr, true);
return(readValue);
}
