zanedubya / ycpu Goto Github PK
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An imaginary 16-bit cpu, with a complete specification, emulator, assembler, and disassembler, in C#.
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# ๐
According to the docs, segment bits 0x00
would translate to (0x00 << 8) + 256 = 256
:
Lines 958 to 959 in d0a1248
but this part of the docs says that 0x00
translates to size 0x10000
:
Line 980 in d0a1248
also from the code it seems like 0x00
would translate to 0x10000
if I'm not mistaken:
YCPU/Source/Libraries/YpsilonCPU/Emulation/Processor/Segment.cs
Lines 154 to 156 in d0a1248
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.
Line 559 in 0af90f8
In 4.A (ALU Bit Pattern), user can only write to FL
, PC
, and USP
, but not PS
.
Lines 1342 to 1355 in 0af90f8
Additionally, in the C# source, user cannot read from PS
.
YCPU/Source/Libraries/YpsilonCPU/Emulation/Processor/YCPU.cs
Lines 163 to 166 in 0af90f8
I think 4.A makes sense, but I'm not sure if user should be able to read PS
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