diff --git a/bmc/main.cpp b/bmc/main.cpp
index ab7ece8..bc25ff0 100644
--- a/bmc/main.cpp
+++ b/bmc/main.cpp
@@ -43,8 +43,14 @@
 namespace
 {
 
+#ifdef NUVOTON_P2A_MBOX
+static constexpr std::size_t memoryRegionSize = 16 * 1024UL;
+#elif defined NUVOTON_P2A_VGA
+static constexpr std::size_t memoryRegionSize = 4 * 1024 * 1024UL;
+#else
 /* The maximum external buffer size we expect is 64KB. */
 static constexpr std::size_t memoryRegionSize = 64 * 1024UL;
+#endif
 
 static constexpr const char* jsonConfigurationPath =
     "/usr/share/phosphor-ipmi-flash/";
@@ -62,11 +68,7 @@
 #endif
 
 #ifdef ENABLE_PCI_BRIDGE
-#if defined(ASPEED_P2A)
 PciDataHandler pciDataHandler(MAPPED_ADDRESS, memoryRegionSize);
-#else
-#error "You must specify a hardware implementation."
-#endif
 #endif
 
 std::vector<DataHandlerPack> supportedTransports = {