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

Index: src/device/rcp/mi/mi_controller.h
--- src/device/rcp/mi/mi_controller.h.orig
+++ src/device/rcp/mi/mi_controller.h
@@ -57,7 +57,7 @@ struct mi_controller
 
 static osal_inline uint32_t mi_reg(uint32_t address)
 {
-    return (address & 0xffff) >> 2;
+    return (address & 0xf) >> 2;
 }
 
 void init_mi(struct mi_controller* mi, struct r4300_core* r4300);
