dwt: visual injection experiments via the returning rdebug jump

dwt/visual/frame_clock.lua

@@ -0,0 +1,25 @@
+-- frame_clock.lua -- read-only frame counter side channel for host-driven tests.
+--
+-- Writes the current frame number to $FRAME_CLOCK once per frame so a host
+-- client can align an injection with a known emulated frame (and therefore with
+-- the driver's VT1200_DUMP_FRAMES schedule).  No breakpoints, no memory writes
+-- except this file.  Optionally exits at $FRAME_STOP.
+local machine = manager.machine
+local path = os.getenv("FRAME_CLOCK")
+local stop = tonumber(os.getenv("FRAME_STOP") or "0")
+local f = 0
+
+emu.register_frame_done(function()
+	f = f + 1
+	if path then
+		local fh = io.open(path, "w")
+		if fh then
+			fh:write(string.format("%d\n", f))
+			fh:close()
+		end
+	end
+	if stop > 0 and f >= stop then
+		print(string.format("frame_clock: stopping at frame %d", f))
+		machine:exit()
+	end
+end, "vt1200-frame-clock")