emu_main: IGC drain-wait hook (0xf0421510): firmware polls [r16] until the rasterizer consumes the region queue; we consume instantly

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

emulator/firmware-decomp/emu_main.py

@@ -60,6 +60,7 @@ MAPS = {
         # (PFAM/PFMAM families, FLAGM->MPIPE, sp/rp bit swap, fdest bypass) makes
         # the firmware's own Newton-Raphson divide compute correctly.
         intdiv=None,
+        igcwait=0xf0421510,               # post-flush IGC drain poll (ld.l 0(r16))
         seeds=[
             (0x1000, 0),                  # _processorId
         ],
@@ -106,8 +107,16 @@ class MainRunner:
         if m['putchar']:  self.hooks[m['putchar']] = self.h_console
         if m['chain']:    self.hooks[m['chain']] = self.h_chainfix
         if m.get('intdiv'): self.hooks[m['intdiv']] = self.h_intdiv
+        if m.get('igcwait'): self.hooks[m['igcwait']] = self.h_igcwait
         self.heap = [0x08010000, 0x0c010000]   # bump allocator over the DRAM banks
 
+    def h_igcwait(self, cpu):
+        # Post-flush drain wait: the firmware polls [r16] until the IGC clears
+        # it after consuming the region queue. We are the IGC: consume instantly.
+        cpu.mem.w32(cpu.rd(16), 0)
+        cpu.step()
+        return True
+
     def h_intdiv(self, cpu):
         # Runtime integer divide (r22 = r22/r23, result via ftrunc+fxfr): the
         # compiled Newton-Raphson relies on exact dual-op pipeline timing our