From 090b432b90577e968557d32f84c4f2ed7fe97f57 Mon Sep 17 00:00:00 2001
From: uvok
Date: Sun, 25 Jan 2026 16:26:55 +0100
Subject: eater: test subtraction

---
 eater_cpu/eater_computer_tb.sv | 10 ++++++++++
 1 file changed, 10 insertions(+)

(limited to 'eater_cpu')

diff --git a/eater_cpu/eater_computer_tb.sv b/eater_cpu/eater_computer_tb.sv
index eab7b23..cc024f4 100644
--- a/eater_cpu/eater_computer_tb.sv
+++ b/eater_cpu/eater_computer_tb.sv
@@ -120,6 +120,16 @@ initial begin
   assert (uut.ALU_flags_int.Carry == 1)
   else   $error("Expected carry flag from ALU, got it not.");
 
+  uut.manual_flags.ALU_subtract_nadd = 1;
+
+  @(negedge clk_in);
+  assert (uut.bus == 8'('haa - 'hbb))
+  else   $error("Expected 0x%02x (from ALU), got 0x%02x on bus", 8'('haa - 'hbb), uut.bus);
+
+  assert (uut.ALU_flags_int.Carry == 1)
+  else   $error("Expected carry flag from ALU, got it not.");
+
+  uut.manual_flags.ALU_subtract_nadd = 0;
   uut.manual_flags.ALU_out = 0;
   uut.manual_flags.PC_out = 1;
 
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