eater: PC inc included, decode on negedgemain

Some cycles can be saved.
As previously (wrongly) committed, the PC can be incremented early,
but the decoder needs to do this "early", so as now implemented,
on the falling clock adge already.

1 files changed, 14 insertions, 7 deletions

diff --git a/eater_cpu/eater_decoder.sv b/eater_cpu/eater_decoder.sv
index 634102a..e18d20d 100644
--- a/eater_cpu/eater_decoder.sv
+++ b/eater_cpu/eater_decoder.sv
@@ -47,11 +47,12 @@ always @(posedge clk_i) begin
 
     INIT: next_state = PC_to_MAR;
 
-    PC_to_MAR: next_state = MEM_to_INS;
+    // PC_to_MAR: next_state = MEM_to_INS;
+    // MEM_to_INS: next_state = PC_inc;
+    // PC_inc: next_state = insdep_state();
 
-    MEM_to_INS: next_state = PC_inc;
-
-    PC_inc: next_state = insdep_state();
+    PC_to_MAR: next_state = MEM_to_INS_PC_inc;
+    MEM_to_INS_PC_inc: next_state = insdep_state();
 
     LDA_INS_to_MAR: next_state = LDA_MEM_to_A;
     LDA_MEM_to_A: next_state = PC_to_MAR;
@@ -101,11 +102,17 @@ always_comb begin
         internal_flags.PC_out = 1;
         internal_flags.MAR_in = 1;
     end
-    MEM_to_INS: begin
+    // MEM_to_INS: begin
+    //     internal_flags.RAM_out = 1;
+    //     internal_flags.INS_in = 1;
+    // end
+    // PC_inc: begin
+    //     internal_flags.PC_count = 1;
+    // end
+
+    MEM_to_INS_PC_inc: begin
         internal_flags.RAM_out = 1;
         internal_flags.INS_in = 1;
-    end
-    PC_inc: begin
         internal_flags.PC_count = 1;
     end