zanedubya / ycpu Goto Github PK

RegControl cr = (RegControl)((operand & 0x0700) >> 8);
Appears to be reading bits A98 (rrE per spec). Should have (operand & 0x0E00)
Apparently I'm writing an issue rather than a PR just to keep my cool kid rep as someone who's never written any C# 😛

According to the docs, segment bits 0x00 would translate to (0x00 << 8) + 256 = 256:

but this part of the docs says that 0x00 translates to size 0x10000:

also from the code it seems like 0x00 would translate to 0x10000 if I'm not mistaken:

So, which one is correct?

According to cartridge.txt, the cartridge puts the return value for messages in R0 register, but from the YCPU spec, R0 is reserved for message acknowledgement (MSG_ACK, MSG_WAIT, MSG_ERROR).

Should the return value be stored in R1 or R2 instead? (In the meantime I'll use R1 in my implementation.)

Suggested fix:

    private void BitPatternBTI(ushort operand, out ushort value, out RegGeneral destination) {
        destination = (RegGeneral)((operand & 0xE000) >> 13); // bits DEF
        RegGeneral source = (RegGeneral)((operand & 0x0F00) >> 8);
        bool asRegister = (operand & 0x1000) != 0;
        value = asRegister ?
            (ushort)(R[(int)source] & 0x000F) :
            (ushort)((operand & 0x1E00) >> 9);
    }

Segments will allow a much larger program space, and better ability to move data!

In 3.B, it is implied that user cannot write to FL, PC, PS, and SP, although they all can still be read.

In 4.A (ALU Bit Pattern), user can only write to FL, PC, and USP, but not PS.

Additionally, in the C# source, user cannot read from PS.

I think 4.A makes sense, but I'm not sure if user should be able to read PS. 🤔