"Implement register mirroring"
https://github.com/mupen64plus/mupen64plus-core/pull/1119

Index: src/device/rcp/ai/ai_controller.c
--- src/device/rcp/ai/ai_controller.c.orig
+++ src/device/rcp/ai/ai_controller.c
@@ -180,7 +180,7 @@ void read_ai_regs(void* opaque, uint32_t address, uint
             ai->last_read = *value;
         }
     }
-    else
+    else if (reg < AI_REGS_COUNT)
     {
         *value = ai->regs[reg];
     }
@@ -216,7 +216,10 @@ void write_ai_regs(void* opaque, uint32_t address, uin
         return;
     }
 
-    masked_write(&ai->regs[reg], value, mask);
+    if (reg < AI_REGS_COUNT)
+    {
+        masked_write(&ai->regs[reg], value, mask);
+    }
 }
 
 void ai_end_of_dma_event(void* opaque)
