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[/] [a-z80/] [trunk/] [tools/] [dongle/] [sbc/] [simulate-sub.py] - Blame information for rev 8

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1 8 gdevic
#!/usr/bin/env python3
2 3 gdevic
#
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# This script simulates 'sub' calculation and generates values for selected numbers.
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# These can be compared with a real Z80 run values.
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#
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import sys
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def printFlags(f):
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    s = ''
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    if f & (1 << 7):
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        s += 'S'
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    else:
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        s += ' '
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    if f & (1 << 6):
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        s += 'Z'
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    else:
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        s += ' '
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    if f & (1 << 5):
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        s += 'Y'
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    else:
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        s += ' '
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    if f & (1 << 4):
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        s += 'H'
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    else:
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        s += ' '
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    if f & (1 << 3):
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        s += 'X'
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    else:
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        s += ' '
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    if f & (1 << 2):
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        s += 'P'
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    else:
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        s += ' '
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    if f & (1 << 1):
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        s += 'V'
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    else:
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        s += ' '
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    if f & (1 << 0):
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        s += 'C'
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    else:
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        s += ' '
42 8 gdevic
    print ('Flags =                           %s' % s)
43 3 gdevic
 
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def sbc(inA, op2, CYin):
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    print ('------------------------------------------')
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    print ('Input: %0.2X SUB %0.2X' % ( inA, op2))
47 3 gdevic
 
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    cplA = inA ^ 0xFF               # Bit-wise complement of A
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    CYin = 1
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    finalA = cplA + 0 + CYin
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    finalA = finalA + op2
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    # Calculate CF while we have bit [9] available
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    cf = 0
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    if finalA > 255 or finalA < 0:
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        cf = 1
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    cf ^= 1                         # Complement CY since we used cpl(A) and not A
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    nf = 1                          # 1 for SUB operation
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    finalA = finalA & 0xFF          # Clamp final value to 8 bits
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    #-------------------------------------------------------------------------------
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    # Flag calculation: SF, ZF, YF, HF, XF, VF/PF, NF, CF
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    #-------------------------------------------------------------------------------
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    # Carry and Overflow calculation on Z80 require us to use internal carry-ins
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    # http://stackoverflow.com/questions/8034566/overflow-and-carry-flags-on-z80
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    carry_ins = finalA ^ inA ^ op2  # Bitfield of all internal carry-ins
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    sf = (finalA>>7) & 1            # SF = Copy of [7]
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    zf = finalA==0                  # ZF = Set if all result bits are zero
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    yf = (finalA>>5) & 1            # YF = Copy of [5]
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    hf = (carry_ins>>4)&1           # HF = Internal carry from bit [3] to [4]
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    xf = (finalA>>3) & 1            # XF = Copy of [3]
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    #                               # PF = XOR all final bits to get odd parity value
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    pf = (((finalA>>7)^(finalA>>6)^(finalA>>5)^(finalA>>4)^(finalA>>3)^(finalA>>2)^(finalA>>1)^(finalA>>0))&1)^1
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    vf = (carry_ins>>7)&1           # VF = Internal carry from bit [6] to [7]
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    vf ^= cf                        # XOR'ed with the final carry out
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    flags = (sf<<7) | (zf<<6) | (yf<<5) | (hf<<4) | (xf<<3) | (vf<<2) | (nf<<1) | (cf<<0)
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82 8 gdevic
    print ('Out:      A -> %0.2X    Flags = %0.2X' % ( finalA, flags))
83 3 gdevic
    printFlags(flags)
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sbc(0, 0, 0)
86 8 gdevic
print ('Should be A -> 00    Flags = 42')
87 3 gdevic
printFlags(0x42)
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sbc(0, 1, 0)
89 8 gdevic
print ('Should be A -> FF    Flags = BB')
90 3 gdevic
printFlags(0xBB)
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sbc(0xAA, 0x55, 0)
93 8 gdevic
print ('Should be A -> 55    Flags = 06')
94 3 gdevic
printFlags(0x06)
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sbc(0x55, 0xAA, 0)
96 8 gdevic
print ('Should be A -> AB    Flags = BF')
97 3 gdevic
printFlags(0xBF)
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sbc(0x0F, 0x03, 0)
100 8 gdevic
print ('Should be A -> 0C    Flags = 0A')
101 3 gdevic
printFlags(0x0A)

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