Fixed ALU Carry/Borrow Flag for SBC

CPUKit_ASBUILT/PLD/ALU/ALU.PLD

@@ -48,9 +48,14 @@ FIELD aluop = [FUNC0..2];
 /* Invert the B input bits for SUB functions */
 [B0..15] = aluop:['d'0,'d'2,'d'3,'d'4,'d'5,'d'6,'d'7]&[BBUS0..15] # aluop:['d'1]&!([BBUS0..15]);
 
-/* Setup Carry-in for addition or subtraction, and if the with carry flag is active. */
+/* Setup Carry-in for addition or subtraction, and if the with carry flag is active.
+   For addition, the carry bit equals 1 to  indicates a carry from the previous op.
+   For subtraction, the carry bit equals 0 to indicate a borrow from the previous op.
+   This is the opposite of X86 and 68K, but the same as ARM,6502.
+
+    */
 C0 =   (aluop:['d'2] & CFOut & (!ALU_WC) )       // inst=ADD: if WC==0 Cin=CF else Cin=0
-     # (aluop:['d'1] & ( (!CFOut) # ALU_WC));    // inst=SUB: if WC==0 Cin=!CF else Cin=1
+     # (aluop:['d'1] & ( (CFOut) # ALU_WC));    // inst=SUB: if WC==0 Cin=CF else Cin=1
 
 P0 = A0 $ B0;
 G0 = A0 & B0;

asm/pygen.py

@@ -0,0 +1,69 @@
+maxq=maxn=maxr=maxk=maxl=maxt=0
+
+def calcPi(limit):  # Generator function
+    """
+    Prints out the digits of PI
+    until it reaches the given limit
+    """
+
+    q, r, t, k, n, l = 1, 0, 1, 1, 3, 3
+
+
+    decimal = limit
+    counter = 0
+
+    while counter != decimal + 1:
+            if 4 * q + r - t < n * t:
+                    # yield digit
+                    yield n
+                    # insert period after first digit
+                    if counter == 0:
+                            yield '.'
+                    # end
+                    if decimal == counter:
+                            print('')
+                            break
+                    counter += 1
+                    nr = 10 * (r - n * t)
+                    n = ((10 * (3 * q + r)) // t) - 10 * n
+                    q *= 10
+                    r = nr
+                    maxn=max(n,maxn)
+                    maxq=max(q,maxq)
+                    maxr=max(r,maxr)
+
+            else:
+                    nr = (2 * q + r) * l
+                    nn = (q * (7 * k) + 2 + (r * l)) // (t * l)
+                    q *= k
+                    t *= l
+                    l += 2
+                    k += 1
+                    n = nn
+                    r = nr
+                    maxn=max(n,maxn)
+                    maxq=max(q,maxq)
+                    maxr=max(r,maxr)
+                    maxt=max(t,maxt)
+                    maxl=max(l,maxl)
+                    maxk=max(k,maxk)
+
+
+
+
+# Calls CalcPi with the given limit
+pi_digits = calcPi(int(input("Enter the number of decimals to calculate to: ")))
+
+i = 0
+
+# Prints the output of calcPi generator function
+# Inserts a newline after every 40th number
+for d in pi_digits:
+    print(d, end='')
+    i += 1
+    if i == 40:
+        print("")
+        i = 0
+
+
+print("n:",maxn,"q:",maxq)