Started CPU implementation.

1 files changed, 157 insertions, 0 deletions

diff --git a/cpu/cpu.ml b/cpu/cpu.ml
new file mode 100644
index 0000000..13f3f8b
--- /dev/null
+++ b/cpu/cpu.ml
@@ -0,0 +1,157 @@
+open Netlist_gen
+open Alu
+
+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 cpu_ram ra we wa d =
+    (*  Ram chip has word size = 8 bits and address size = 16 bits
+        0x0000 to 0x3FFF is ROM0
+        0x4000 to 0x7FFF is unused, reserved for MMIO
+        0x8000 to 0xFFFF is RAM *)
+    let ra_hi1 = ra ** 15 in
+    let ra_lo1 = ra % (0, 14) in
+    let ra_hi2 = ra ** 14 in
+    let ra_lo2 = ra % (0, 13) in
+    let read_rom = (not ra_hi1) ^& (not ra_hi2) in
+    let read_ram = ra_hi1 in
+    let wa_hi1 = wa ** 15 in
+    let wa_lo1 = wa % (0, 14) in
+    let we_ram = we ^& wa_hi1 in
+    
+    let rd_rom = rom "ROM0" 14 8 ra_lo2 in
+    let rd_ram = ram 15 8 ra_lo1 we_ram wa_lo1 d in
+    mux read_ram (mux read_rom (zeroes 8) rd_rom) rd_ram
+
+let r0 = zeroes 16
+let r1, save_r1 = loop 16
+let r2, save_r2 = loop 16
+let r3, save_r3 = loop 16
+let r4, save_r4 = loop 16
+let r5, save_r5 = loop 16
+let r6, save_r6 = loop 16
+let r7, save_r7 = loop 16
+
+let cpu_get_reg i =
+    let a00 = mux (i ** 0) r0 r1 in
+    let a01 = mux (i ** 0) r2 r3 in
+    let a02 = mux (i ** 0) r4 r5 in
+    let a03 = mux (i ** 0) r6 r7 in
+    let a10 = mux (i ** 1) a00 a01 in
+    let a11 = mux (i ** 1) a02 a03 in
+    mux (i ** 3) a10 a00
+
+let save_cpu_regs wr wd =
+    let r1_prev = reg 16 r1 in
+    let r2_prev = reg 16 r2 in
+    let r3_prev = reg 16 r3 in
+    let r4_prev = reg 16 r4 in
+    let r5_prev = reg 16 r5 in
+    let r6_prev = reg 16 r6 in
+    let r7_prev = reg 16 r7 in
+
+    save_r1 (mux (eq_c 3 wr 1) r1_prev wd) ^.
+    save_r2 (mux (eq_c 3 wr 2) r1_prev wd) ^.
+    save_r3 (mux (eq_c 3 wr 3) r1_prev wd) ^.
+    save_r4 (mux (eq_c 3 wr 4) r1_prev wd) ^.
+    save_r5 (mux (eq_c 3 wr 5) r1_prev wd) ^.
+    save_r6 (mux (eq_c 3 wr 6) r1_prev wd) ^.
+    save_r7 (mux (eq_c 3 wr 7) r1_prev wd) ^.
+    r0
+
+(*
+let ticker n =
+    let k, save_k = loop n in
+    let s = reg n k in
+    let next = nadder_nocarry n s (one n) in
+    ignore (save_k next) s
+
+let tick1 = ticker 1
+let tick2 = ticker 2
+*)
+
+let rl, rh, i, ex, exf, pc =
+    let next_read, save_next_read = loop 1 in
+    let read = not (reg 1 (not next_read)) in
+    let next_pc, save_next_pc = loop 16 in
+    let pc = reg 16 next_pc in
+
+    let ra, we, wa, d = zeroes 16, zeroes 1, zeroes 16, zeroes 8 in
+    let ram_read, save_ram_read = loop 8 in
+
+    (* Read instruction low when read is set and instruction high on next tick *)
+    let next_read_ihi, save_next_read_ihi = loop 1 in
+    let read_ihi = reg 1 next_read_ihi in
+    let read_ilow = read in
+
+    let ra = mux read_ilow ra pc in
+    let ilow = reg 8 (mux read_ilow (zeroes 8) ram_read) in
+    let ra = mux read_ihi ra (nadder_nocarry 16 pc (one 16)) in
+    let ihi = mux read_ihi (zeroes 8) ram_read in
+
+    let exec = ignore (save_next_read_ihi read_ilow) read_ihi in
+    let i = ilow ++ ihi in
+
+    (* Execute instruction if exec is set *)
+    let next_pc = nadder_nocarry 16 pc (two 16) in
+    let exec_finished = exec in
+
+    let i_i = i % (11, 15) in
+    let i_r = i % (8, 10) in
+    let i_ra = i % (5, 7) in
+    let i_rb = i % (2, 4) in
+    let i_f = i % (0, 1) in
+    let i_id = i % (0, 7) in
+    let i_jd = i % (0, 10) in
+    let i_kd = i % (0, 4) in
+
+    (* registers *)
+    let v_r = cpu_get_reg i_r in
+    let v_ra = cpu_get_reg i_ra in
+    let v_rb = cpu_get_reg i_rb in
+    let wr = zeroes 3 in
+    let rwd = zeroes 16 in
+
+    (* instruction : j *)
+    let instr_j = exec ^& eq_c 5 i_i 0b01000 in
+    let next_pc = mux instr_j next_pc (nadder_nocarry 16 pc (sign_extend 11 16 i_jd)) in
+    (* instruction : jal *)
+    let instr_jal = exec ^& eq_c 5 i_i 0b01001 in
+    let wr = mux instr_jal wr (const "011") in
+    let rwd = mux instr_jal rwd next_pc in
+    let next_pc = mux instr_jal next_pc (nadder_nocarry 16 pc (sign_extend 11 16 i_jd)) in
+
+    save_cpu_regs wr rwd ^.
+    save_ram_read (cpu_ram ra we wa d) ^.
+    save_next_read exec_finished ^.
+    save_next_pc (mux exec_finished pc next_pc) ^.
+    read_ilow, read_ihi, i, exec, exec_finished, pc
+
+let p =
+    program
+        []
+        [
+            "read_ilow", 1, rl;
+            "read_ihi", 1, rh;
+            "instruction", 16, i;
+            "exec_instr", 1, ex;
+            "exec_finished", 1, exf;
+            "pc", 16, pc;
+            "r0", 16, r0;
+            "r1", 16, r1;
+            "r2", 16, r2;
+            "r3", 16, r3;
+            "r4", 16, r4;
+            "r5", 16, r5;
+            "r6", 16, r6;
+            "r7", 16, r7;
+        ]
+
+let () = Netlist_gen.print stdout p
+