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[/] [a-z80/] [trunk/] [tools/] [dongle/] [neg/] [simulate-neg.py] - Rev 22
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#!/usr/bin/env python3 # # This script simulates 'neg' calculation and generates values for numbers 0-255. # These can be compared with a real Z80 run values. # import sys for inA in range(0, 256): # neg is: 0 - A # or: 255 - inA + 1 # or: 255 - -(cpl(A)+1) + 1 (second complement of A; can change the sign) # or: 255 + cpl(A)+1 + 1 # or: cpl(A) + 255 + 1 + 1 # or: cpl(A) + 0 + 1 (+CY) # cplA = inA ^ 0xFF; # Bit-wise complement of A # CYin = 1 # Carry in force to 1 # op2 = 0 # Load operand 2 with a constant value of 0 # finalA = cplA + op2 + CYin acct = inA # ACCT is always loaded with A op2 = inA # Load A again into OP2 mux1 = 0 # MUX1 selects 0 instead of ACCT mux2 = op2 ^ 0xFF # MUX2 selects complement of OP2 CYin = 1 # Carry in force to 1 finalA = mux1 + mux2 + CYin carry_ins = finalA ^ mux1 ^ mux2 # Bitfield of all internal carry-ins carry_ins ^= 0x90 # !?!?! Need to invert both H and V carry-ins? # Calculate CF while we have bit [9] available cf = 0 if finalA > 255 or finalA < 0: cf = 1 cf ^= 1 # Complement CY since we used cpl(A) and not A nf = 1 # 1 for SUB operation finalA = finalA & 0xFF # Clamp final value to 8 bits #------------------------------------------------------------------------------- # Flag calculation: SF, ZF, YF, HF, XF, VF/PF, NF, CF #------------------------------------------------------------------------------- # Carry and Overflow calculation on Z80 require us to use internal carry-ins # http://stackoverflow.com/questions/8034566/overflow-and-carry-flags-on-z80 #carry_ins = finalA ^ inA ^ op2 # Bitfield of all internal carry-ins sf = (finalA>>7) & 1 # SF = Copy of [7] zf = finalA==0 # ZF = Set if all result bits are zero yf = (finalA>>5) & 1 # YF = Copy of [5] hf = (carry_ins>>4)&1 # HF = Internal carry from bit [3] to [4] xf = (finalA>>3) & 1 # XF = Copy of [3] # # PF = XOR all final bits to get odd parity value pf = (((finalA>>7)^(finalA>>6)^(finalA>>5)^(finalA>>4)^(finalA>>3)^(finalA>>2)^(finalA>>1)^(finalA>>0))&1)^1 vf = (carry_ins>>7)&1 # VF = Internal carry from bit [6] to [7] vf ^= cf # XOR'ed with the final carry out flags = (sf<<7) | (zf<<6) | (yf<<5) | (hf<<4) | (xf<<3) | (vf<<2) | (nf<<1) | (cf<<0) print ('%0.2X -> %0.2X Flags = %0.2X' % ( inA, finalA, flags))
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