diff options
Diffstat (limited to 'cpu/alu.ml')
| -rw-r--r-- | cpu/alu.ml | 117 |
1 files changed, 110 insertions, 7 deletions
@@ -1,5 +1,13 @@ open Netlist_gen +let zeroes n = + const (String.make n '0') + +let one n = + const "1" ++ zeroes (n-1) +let two n = + const "01" ++ zeroes (n-2) + let rec rep n k = if n = 1 then k else @@ -27,25 +35,55 @@ let rec nonnull n a = let rec sign_extend n_a n_dest a = a ++ rep (n_dest - n_a) (a ** (n_a - 1)) +(* Arithmetic operations *) + let fulladder a b c = let s = a ^^ b ^^ c in let r = (a ^& b) ^| ((a ^^ b) ^& c) in s, r -let rec nadder n a b c_in = +let rec nadder_with_carry n a b c_in = if n = 1 then fulladder a b c_in else let s_n, c_n1 = fulladder (a ** 0) (b ** 0) c_in in - let s_n1, c_out = nadder (n-1) (a % (1, n-1)) (b % (1, n-1)) c_n1 in + let s_n1, c_out = nadder_with_carry (n-1) (a % (1, n-1)) (b % (1, n-1)) c_n1 in s_n ++ s_n1, c_out -let rec npshift_signed n p a b = - a (* TODO *) - -let nadder_nocarry n a b = - let a, b = nadder n a b (const "0") in +let nadder n a b = + let a, b = nadder_with_carry n a b (const "0") in ignore b a +let rec nsubber n a b = + zeroes n (* TODO *) + +let rec nmul n a b = + zeroes n, zeroes n (* TODO : retuns lo and hi part of 32-bit answer *) + +let rec ndiv n a b = + zeroes n, zeroes n (* TODO : returns quotient and remainder *) + +let rec nmulu n a b = + zeroes n, zeroes n (* TODO : same as nmul but unsigned *) + +let rec ndivu n a b = + zeroes n, zeroes n (* TODO : save as ndiv but unsigned *) + +(* Shifts *) + +let npshift_signed n p a b = + a (* TODO (here b is a signed integer on p bits) *) + +let op_lsl n a b = + a (* TODO (b is unsigned, same size n) *) + +let op_lsr n a b = + a (* TODO (b is unsigned, same size n) *) + +let op_asr n a b = + a (* TODO (b unsigned size n) *) + +(* Comparisons *) + let rec eq_n n a b = all1 n (not (a ^^ b)) @@ -64,6 +102,8 @@ let rec le_n n a b = let rec ule_n n a b = const "0" (* TODO : less than or equal, unsigned *) +(* Big pieces *) + let alu_comparer n f0 f a b = (* f0 f action @@ -82,3 +122,66 @@ let alu_comparer n f0 f a b = let lte_unsigned = mux (f ** 0) (ult_n n a b) (ule_n n a b) in let lte = mux (f ** 1) lte_signed lte_unsigned in mux f0 eq_ne lte + +let alu_arith f1 f a b = + (* See table for ALU below *) + let add = nadder 16 a b in + let sub = nsubber 16 a b in + let mul, mul2 = nmul 16 a b in + let div, div2 = ndiv 16 a b in + let mulu, mulu2 = nmulu 16 a b in + let divu, divu2 = ndivu 16 a b in + let q00 = mux (f ** 0) add sub in + let q01 = mux (f ** 0) mul div in + let q03 = mux (f ** 0) mulu divu in + let q10 = mux (f ** 1) q00 q01 in + let q11 = mux (f ** 1) q00 q03 in + let q = mux f1 q10 q11 in + let r01 = mux (f ** 0) mul2 div2 in + let r03 = mux (f ** 0) mulu2 divu2 in + let r10 = mux (f ** 1) (zeroes 16) r01 in + let r11 = mux (f ** 1) (zeroes 16) r03 in + let r = mux f1 r10 r11 in + q, r + +let alu_logic f a b = + (* See table for ALU below *) + let q0 = mux (f ** 0) (a ^| b) (a ^& b) in + let q1 = mux (f ** 0) (a ^^ b) (not (a ^| b)) in + mux (f ** 1) q0 q1 + +let alu_shifts f a b = + (* See table for ALU below *) + let q1 = mux (f ** 0) (op_lsr 16 a b) (op_asr 16 a b) in + mux (f ** 1) (op_lsl 16 a b) q1 + +let alu f1 f0 f a b = + (* + f0 f1 f action + -- -- - ------ + 0 0 0 add + 0 0 1 sub + 0 0 2 mul + 0 0 3 div + 0 1 0 addu + 0 1 1 subu + 0 1 2 mulu + 0 1 3 divu + 1 0 0 or + 1 0 1 and + 1 0 2 xor + 1 0 3 nor + 1 1 0 lsl + 1 1 1 lsl + 1 1 2 lsr + 1 1 3 asr + *) + let arith, arith_r = alu_arith f1 f a b in + let logic = alu_logic f a b in + let shifts = alu_shifts f a b in + + let q0 = mux f1 logic shifts in + let s = mux f0 arith q0 in + let r = mux f0 arith_r (zeroes 16) in + s, r + |