From 3a0c50ca076c3cd94923ee89aea2b885aee06f06 Mon Sep 17 00:00:00 2001
From: uvok
Date: Sun, 25 Jan 2026 16:09:54 +0100
Subject: eater: ALU outputs flags

---
 eater_cpu/eater_alu.sv      |  5 ++++-
 eater_cpu/eater_computer.sv | 15 ++++++++++++++-
 eater_cpu/eater_types.sv    |  6 ++++++
 3 files changed, 24 insertions(+), 2 deletions(-)

(limited to 'eater_cpu')

diff --git a/eater_cpu/eater_alu.sv b/eater_cpu/eater_alu.sv
index b1ed7ea..d8748a4 100644
--- a/eater_cpu/eater_alu.sv
+++ b/eater_cpu/eater_alu.sv
@@ -2,6 +2,8 @@
 
 `timescale 1us/1us
 
+`include "eater_types.sv"
+
 module eater_alu (
     input wire clk_in,
     input wire en_output_in,
@@ -11,7 +13,8 @@ module eater_alu (
     input wire [7:0] A_in,
     input wire [7:0] B_in,
 
-    output wire [7:0] bus_out
+    output wire [7:0] bus_out,
+    output wire AluFlags flags_out
 );
 
 wire [7:0] result /* verilator public */;
diff --git a/eater_cpu/eater_computer.sv b/eater_cpu/eater_computer.sv
index 75a54c9..b22096a 100644
--- a/eater_cpu/eater_computer.sv
+++ b/eater_cpu/eater_computer.sv
@@ -41,6 +41,9 @@ wire [7:0]
       OUT_out
 ;
 
+// ALU flags. int: direct out. out: buffered output (for decoder).
+wire AluFlags ALU_flags_int, ALU_flags_out;
+
 // PC is only 4 bit.
 wire [3:0] PC_in, PC_out;
 
@@ -134,7 +137,8 @@ eater_alu alu (
   .A_in(A_out),
   .B_in(B_out),
   .subtract_n_add_in(flags.ALU_subtract_nadd),
-  .bus_out(bus)
+  .bus_out(bus),
+  .flags_out(ALU_flags_int)
 );
 
 assign PC_in = bus[3:0];
@@ -167,6 +171,15 @@ eater_register OUT_reg (
   .always_out(OUT_out)
 );
 
+eater_register ALU_flags (
+  .clk_in(clk_in),
+  .en_store_in(flags.flags_in),
+  .en_output_in(1'b0),
+  .data_in(ALU_flags_int),
+  .bus_out(),
+  .always_out(ALU_flags_out)
+);
+
 // run decoder on negated clock,
 // allowing stuff to be clocked in "early"
 wire DEC_clk_neg = ~clk_in;
diff --git a/eater_cpu/eater_types.sv b/eater_cpu/eater_types.sv
index b0e5592..3744df1 100644
--- a/eater_cpu/eater_types.sv
+++ b/eater_cpu/eater_types.sv
@@ -73,6 +73,12 @@ typedef enum logic[3:0] {
     HALT_op = 'b1111
 } eater_instruction;
 
+typedef struct packed {
+    logic Zero;
+    logic Carry;
+    logic [5:0] reserved;
+} AluFlags;
+
 // CPU control flags
 `ifdef IVERILOG
 typedef struct packed {
-- 
cgit v1.2.3