From 1f0fc1edcea04e5c1f04803f0bdda337c2245f09 Mon Sep 17 00:00:00 2001
From: uvok
Date: Mon, 19 Jan 2026 19:43:58 +0100
Subject: eater: Combine counting in prev. state

save 1 cycle, as explained in video.
also, only print lo->hi clk states to term.
---
 eater_cpu/cpp/Veater_computer__main.cpp |  2 +-
 eater_cpu/cpp/simpc_term.cpp            |  3 +++
 eater_cpu/eater_decoder.sv              | 10 +++-------
 eater_cpu/eater_types.sv                |  3 +--
 eater_cpu/readme.txt                    |  6 ++----
 5 files changed, 10 insertions(+), 14 deletions(-)

(limited to 'eater_cpu')

diff --git a/eater_cpu/cpp/Veater_computer__main.cpp b/eater_cpu/cpp/Veater_computer__main.cpp
index 425fa4e..315d52a 100644
--- a/eater_cpu/cpp/Veater_computer__main.cpp
+++ b/eater_cpu/cpp/Veater_computer__main.cpp
@@ -65,7 +65,7 @@ int main(int argc, char **argv, char **) {
 
     topp->clk_in = !topp->clk_in;
 
-    if (topp->eater_computer->PC_out == 3 &&
+    if (topp->eater_computer->PC_out == 4 &&
         topp->eater_computer->decoder__DOT__internal_state == 0x01)
       break;
   }
diff --git a/eater_cpu/cpp/simpc_term.cpp b/eater_cpu/cpp/simpc_term.cpp
index 8ddf83d..540cc98 100644
--- a/eater_cpu/cpp/simpc_term.cpp
+++ b/eater_cpu/cpp/simpc_term.cpp
@@ -36,6 +36,9 @@ bool paused = false;
 static void handle_key();
 
 void simpc_ui_write(const std::unique_ptr<Veater_computer> &topp, uint64_t i) {
+  // clk hi->lo doesn't do anything, just skip this.
+  if (i !=0 && !topp->clk_in)
+    return;
   // uint16_t opcode = topp->eater_computer->;
   uint8_t opcode = topp->eater_computer->INS->r_datastore;
   // topp->halt
diff --git a/eater_cpu/eater_decoder.sv b/eater_cpu/eater_decoder.sv
index d2ea9cc..78d4e6c 100644
--- a/eater_cpu/eater_decoder.sv
+++ b/eater_cpu/eater_decoder.sv
@@ -41,11 +41,9 @@ 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_and_PC_inc;
 
-    MEM_to_INS: next_state = PC_inc;
-
-    PC_inc: next_state = insdep_state();
+    MEM_to_INS_and_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;
@@ -81,11 +79,9 @@ always_comb begin
         internal_flags.PC_out = 1;
         internal_flags.MAR_in = 1;
     end
-    MEM_to_INS: begin
+    MEM_to_INS_and_PC_inc: begin
         internal_flags.RAM_out = 1;
         internal_flags.INS_in = 1;
-    end
-    PC_inc: begin
         internal_flags.PC_count = 1;
     end
 
diff --git a/eater_cpu/eater_types.sv b/eater_cpu/eater_types.sv
index 6be4d9d..6061a03 100644
--- a/eater_cpu/eater_types.sv
+++ b/eater_cpu/eater_types.sv
@@ -8,8 +8,7 @@ typedef enum logic[7:0] {
     // "regular" states
     INIT,
     PC_to_MAR,
-    MEM_to_INS,
-    PC_inc,
+    MEM_to_INS_and_PC_inc,
 
     // instruction dependent states
 
diff --git a/eater_cpu/readme.txt b/eater_cpu/readme.txt
index f92fdd7..9ff0090 100644
--- a/eater_cpu/readme.txt
+++ b/eater_cpu/readme.txt
@@ -40,10 +40,8 @@ operation
    Increment PC.
    a) PC out -> MAR
    (PC_to_bus) + (bus_to_MAR) + (clk)
-   b) MEM -> INS
-   (RAM_to_bus) + (bus_to_INS) + (clk)
-   c) PC++
-   (PC_count_en) + (clk)
+   b) MEM -> INS, PC++
+   (RAM_to_bus) + (bus_to_INS) + (PC_count_en) + (clk)
 
 2. Decode and execute instruction.
 
-- 
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