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

Index: src/device/rdram/rdram.c
--- src/device/rdram/rdram.c.orig
+++ src/device/rdram/rdram.c
@@ -173,7 +173,11 @@ void read_rdram_regs(void* opaque, uint32_t address, u
         return;
     }
 
-    *value = rdram->regs[module][reg];
+    if (reg < RDRAM_REGS_COUNT) {
+        *value = rdram->regs[module][reg];
+    } else {
+        *value = 0;
+    }
 
     /* some bits are inverted when read */
     if (reg == RDRAM_MODE_REG) {
@@ -187,6 +191,10 @@ void write_rdram_regs(void* opaque, uint32_t address, 
     uint32_t reg = rdram_reg(address);
     size_t module;
     size_t modules = get_modules_count(rdram);
+
+    if (reg >= RDRAM_REGS_COUNT) {
+        return;
+    }
 
     /* HACK: Detect when current Control calibration is about to start,
      * so we can set corrupted rdram_dram handler
