/// <summary>
/// Translates the instruction and sets the Code property.
/// If an error is detected, Error property is set instead.
/// </summary>
/// <returns>A value indicating if the translation was successful</returns>
public override bool Translate()
{
Error = null;
if (!CheckArgument1())
{
return(false);
}
Code = new ushort[2];
Code[0] = 0xD << 12; // The first word is always the same (only an OPCode).
int value;
Argument1.LookUpValue(Assembler, out value);
Code[1] = (ushort)value; // The second word is the address of the subroutine.
return(true);
}
/// <summary>
/// Translates the first argument to the machine code.
/// The resulting value contains the argument encoding in the right
/// position within the word, and zeroes in locations intended for the
/// OPCode (mnemonic) and the other argument.
/// </summary>
/// <returns>A value containing the translation of the argument</returns>
protected ushort TranslateArgument1()
{
int value;
Argument1.LookUpValue(Assembler, out value);
// Write address to the lowest 3 bits
ushort result = (ushort)value;
if (Argument1.Type == ArgumentType.Indirect)
{
// Indirect addressing is indicated by setting the 4th lowest bit.
result |= 0x8;
}
// Move the argument to the right position : 0000aaaa00000000
result <<= 8;
return(result);
}
/// <summary>
/// Checks if the first argument is valid.
/// </summary>
/// <remarks>
/// The first argument of an I/O instruction must be a symbol
/// present in the symbol table and its value must be between [0..7].
/// </remarks>
/// <returns>A value indicating if Argument1 is valid</returns>
protected bool CheckArgument1()
{
int value;
if (!Argument1.LookUpValue(Assembler, out value))
{
return(false);
}
if (value < 0 || value > 7)
{
Error = new Error();
Error.ID = 3;
Error.Description = string.Format(Messages.E0003, Argument1.Text, 0, 7);
Error.Line = Line;
Error.Column = Argument1.Column;
return(false);
}
return(true);
}