From 5742e1f66c4e70151865de7092547223898bbf6b Mon Sep 17 00:00:00 2001
From: Julian Blake Kongslie
Date: Sun, 18 Apr 2021 16:00:54 -0700
Subject: Support a proper PDP-8 assembler.

---
 tool/pll.rb | 23 +++++++++++++++++++++++
 1 file changed, 23 insertions(+)
 create mode 100755 tool/pll.rb

(limited to 'tool/pll.rb')

diff --git a/tool/pll.rb b/tool/pll.rb
new file mode 100755
index 0000000..49464d4
--- /dev/null
+++ b/tool/pll.rb
@@ -0,0 +1,23 @@
+#!/usr/bin/ruby -w
+
+TARGET_FREQ = ARGV.shift.to_f
+NATIVE_FREQ = 50.0
+
+CLOCK_WIDTH = 5
+
+best = nil
+best_mult = nil
+best_div = nil
+1.upto(2**CLOCK_WIDTH) do | mult |
+  1.upto(2**CLOCK_WIDTH) do | div |
+    new = NATIVE_FREQ * mult / div
+    if not best or (new - TARGET_FREQ).abs < (best - TARGET_FREQ).abs or ((new - TARGET_FREQ).abs == (best - TARGET_FREQ).abs and (mult + div) < (best_mult + best_div))
+      best = new
+      best_mult = mult
+      best_div = div
+    end
+  end
+end
+
+error = (best - TARGET_FREQ).abs / TARGET_FREQ
+$stdout.write("Closest I can get is #{best}: *#{best_mult} /#{best_div} (#{(error * 100).round}% error)\n")
-- 
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