add epona glitch monitoring script

Lua/README.md

@@ -12,7 +12,7 @@ Note that some scripts lack full support for Ocarina of Time.
 
 ## Scripts
 
-#### actor listor.lua
+#### actor lister.lua
 Lists actor data onscreen,
 and focuses the camera on them.
 Actors may be selected using the D-Pad.
@@ -70,6 +70,11 @@ These scripts look for changes in RAM regions and print them in detail.
 
 These are mostly used for documenation.
 
+#### epona monitor.lua
+used to investigate [this glitch with unloading Epona.][eponaglitch]
+
+[eponaglitch]: https://www.youtube.com/watch?v=kX0ZcIS8P84
+
 #### event flag monitor.lua
 Monitors event flags,
 and announces which bits are being changed,

Lua/epona monitor.lua

@@ -0,0 +1,47 @@
+require = require "depend"
+require "boilerplate"
+require "addrs.init"
+require "messages"
+require "actors"
+
+local actor_names = require "data.actor names"
+
+local epona_addr = 0
+while true do
+    local nearest = {}
+    local offset = 0x800000
+
+    for at, ai, addr in iter_actors() do
+        local actor_number = R2(addr)
+        local name = actor_names[actor_number]
+        local size = R4(addr - 0xC) -- read linked list data above the actor
+        if actor_number == 0x00D then
+            epona_addr = addr
+        end
+
+        if epona_addr then
+            local diff = addr - epona_addr
+            if diff >= 0 and diff < offset then
+                offset = diff
+                nearest.name = name or "[error]"
+                nearest.addr = addr
+                nearest.at = at
+                nearest.ai = ai
+                nearest.size = size
+            end
+        end
+    end
+
+    if nearest.addr then
+        local color = offset <= nearest.size and 'white' or 'yellow'
+        T_BR(0, 4, 'white', 'Epona: %06X', epona_addr)
+        T_BR(0, 3, 'white', '%s: %06X', nearest.name, nearest.addr)
+        T_BR(0, 2, color, 'Offset: %06X', offset)
+        T_BR(0, 1, color, 'Size: %06X', nearest.size)
+        T_BR(0, 0, 'white', 'Type, Index: %2i, %2i', nearest.at, nearest.ai)
+    else
+        T_BR(0, 0, 'yellow', 'Epona not found')
+    end
+
+    emu.frameadvance()
+end