11 files changed, 387 insertions, 65 deletions

diff --git a/src/Makefile b/src/Makefile
index 888110f..c997ae3 100644
--- a/src/Makefile
+++ b/src/Makefile
@@ -225,6 +225,7 @@ tests: test_bip32 test_compactblock bitflash-node
         ./bitflash-node -selftest=wallet-crypto
         ./bitflash-node -selftest=wallet-encrypt
         ./bitflash-node -selftest=net-message
+        ./bitflash-node -selftest=network-params
         ./bitflash-node -selftest=consensus-limits
         ./bitflash-node -selftest=pool-stratum
         ./bitflash-node -selftest=payout-ledger
diff --git a/src/main.cpp b/src/main.cpp
index 7398064..0fa6b89 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -42,12 +42,30 @@ unsigned int nTransactionsUpdated = 0;
 map<COutPoint, CInPoint> mapNextTx;
 
 map<uint256, CBlockIndex*> mapBlockIndex;
-// Bitflash genesis -- mined under RandomX PoW on 2026-07-22
-// (nTime 1753142400, nBits 0x1f0fffff, RandomX key "Bitflash/RandomX/v1/...")
-// Bitflash 2026 stable relaunch genesis (2-min blocks, RandomX). Mined values.
-unsigned int GENESIS_NONCE = 3141;
-uint256 hashGenesisBlock("0x5bd7cb255d814e48cebcdfb72da4dc87b34bd774227f8ceb546c5640f4bdc169");
-uint256 hashGenesisMerkleRoot("0x1a45b4482532abb29b10e234d3f13132230525a339ecea91658ffa675a5b1325");
+// Bitflash mainnet genesis -- mined under RandomX PoW for the 2026 stable
+// relaunch. Testnet gets its own resettable genesis below so block indexes,
+// headers, and wallet scans cannot be accidentally mixed across networks.
+static const unsigned int MAINNET_GENESIS_TIME  = 1753315200; // 2026-07-24 00:00:00 UTC
+static const unsigned int MAINNET_GENESIS_NONCE = 3141;
+static const char* MAINNET_GENESIS_TIMESTAMP =
+    "Bitflash 24/Jul/2026 Fair launch: one CPU one vote, no premine";
+static const char* MAINNET_GENESIS_HASH =
+    "0x5bd7cb255d814e48cebcdfb72da4dc87b34bd774227f8ceb546c5640f4bdc169";
+static const char* MAINNET_GENESIS_MERKLE =
+    "0x1a45b4482532abb29b10e234d3f13132230525a339ecea91658ffa675a5b1325";
+
+static const unsigned int TESTNET_GENESIS_TIME  = 1787184000; // 2026-08-20 00:00:00 UTC
+static const unsigned int TESTNET_GENESIS_NONCE = 3199;
+static const char* TESTNET_GENESIS_TIMESTAMP =
+    "Bitflash testnet 20/Aug/2026: resettable public test chain";
+static const char* TESTNET_GENESIS_HASH =
+    "0xa9d11c6d697bcb7aea0653bc088b12dcf9f44e732df205162cf085fd9d9963eb";
+static const char* TESTNET_GENESIS_MERKLE =
+    "0x510b293105e3ff85b8d4c3920e357f85d1a86bf199eb4e7d11f04f380030ec5c";
+
+unsigned int GENESIS_NONCE = MAINNET_GENESIS_NONCE;
+uint256 hashGenesisBlock(MAINNET_GENESIS_HASH);
+uint256 hashGenesisMerkleRoot(MAINNET_GENESIS_MERKLE);
 CBlockIndex* pindexGenesisBlock = NULL;
 int nBestHeight = -1;
 uint256 hashBestChain = 0;
@@ -254,6 +272,63 @@ static std::atomic<uint64> gParticipantHashRateX1000{0};
 static std::mutex gParticipantStatusMutex;
 static std::string gParticipantStatus;
 
+void SelectGenesisParams(bool fTestNetIn)
+{
+    static bool fGenesisParamsSelected = false;
+    static bool fGenesisParamsTestNet = false;
+    if (fGenesisParamsSelected && fGenesisParamsTestNet == fTestNetIn)
+        return;
+
+    fGenesisParamsSelected = true;
+    fGenesisParamsTestNet = fTestNetIn;
+
+    if (fTestNetIn)
+    {
+        GENESIS_NONCE = TESTNET_GENESIS_NONCE;
+        hashGenesisBlock = uint256(TESTNET_GENESIS_HASH);
+        hashGenesisMerkleRoot = uint256(TESTNET_GENESIS_MERKLE);
+    }
+    else
+    {
+        GENESIS_NONCE = MAINNET_GENESIS_NONCE;
+        hashGenesisBlock = uint256(MAINNET_GENESIS_HASH);
+        hashGenesisMerkleRoot = uint256(MAINNET_GENESIS_MERKLE);
+    }
+}
+
+void SelectChainParams(bool fTestNetIn)
+{
+    SelectNetworkParams(fTestNetIn);
+    SelectGenesisParams(fTestNetIn);
+}
+
+static CBlock BuildGenesisBlock()
+{
+    const char* pszTimestamp = IsTestNet() ?
+        TESTNET_GENESIS_TIMESTAMP : MAINNET_GENESIS_TIMESTAMP;
+
+    CTransaction txNew;
+    txNew.vin.resize(1);
+    txNew.vout.resize(1);
+    txNew.vin[0].scriptSig = CScript() << 486604799 << CBigNum(4) <<
+        vector<unsigned char>((unsigned char*)pszTimestamp,
+                              (unsigned char*)pszTimestamp + strlen(pszTimestamp));
+    txNew.vout[0].nValue = 50 * COIN;
+    txNew.vout[0].scriptPubKey = CScript() <<
+        CBigNum("0x5F1DF16B2B704C8A578D0BBAF74D385CDE12C11EE50455F3C438EF4C3FBCF649B6DE611FEAE06279A60939E028A8D65C10B73071A6F16719274855FEB0FD8A6704") <<
+        OP_CHECKSIG;
+
+    CBlock block;
+    block.vtx.push_back(txNew);
+    block.hashPrevBlock = 0;
+    block.hashMerkleRoot = block.BuildMerkleTree();
+    block.nVersion = 1;
+    block.nTime = IsTestNet() ? TESTNET_GENESIS_TIME : MAINNET_GENESIS_TIME;
+    block.nBits = 0x1f0fffff; // = bnProofOfWorkLimit (Bitflash RandomX floor)
+    block.nNonce = GENESIS_NONCE;
+    return block;
+}
+
 void SetParticipantMiningStatus(const std::string& status)
 {
     // Updates the GUI status string only. Logging is done at each call site
@@ -2654,11 +2729,21 @@ string GetAppDir()
     {
         return ".";
     }
-    static bool fMkdirDone;
-    if (!fMkdirDone)
+    static string strCreatedBaseDir;
+    if (strCreatedBaseDir != strDir)
     {
-        fMkdirDone = true;
         _mkdir(strDir.c_str());
+        strCreatedBaseDir = strDir;
+    }
+    if (IsTestNet())
+    {
+        strDir += "/testnet";
+        static string strCreatedTestnetDir;
+        if (strCreatedTestnetDir != strDir)
+        {
+            _mkdir(strDir.c_str());
+            strCreatedTestnetDir = strDir;
+        }
     }
     return strDir;
 }
@@ -2812,38 +2897,34 @@ bool LoadBlockIndex(bool fAllowNew)
 
         // Bitflash genesis block -- own header (fair launch)
         //
-        // Do not change pszTimestamp, the scriptPubKey, nTime or nNonce. They
-        // are the inputs to the genesis hash, and the genesis hash is
-        // consensus. Changing one on its own trips the assert below, which is
-        // loud and reverts cleanly; changing one and regenerating
-        // GENESIS_NONCE and hashGenesisBlock to match -- which is exactly what
-        // the re-mining branch below prints out and invites -- gives a node
-        // that starts without complaint, builds its own chain from height 0,
-        // and rejects every real peer as being on a different chain. That one
-        // fails silently, and the damage scales with how many people run the
-        // "fixed" build.
-        char* pszTimestamp = "Bitflash 24/Jul/2026 Fair launch: one CPU one vote, no premine";
-        CTransaction txNew;
-        txNew.vin.resize(1);
-        txNew.vout.resize(1);
-        txNew.vin[0].scriptSig     = CScript() << 486604799 << CBigNum(4) << vector<unsigned char>((unsigned char*)pszTimestamp, (unsigned char*)pszTimestamp + strlen(pszTimestamp));
-        txNew.vout[0].nValue       = 50 * COIN;
-        txNew.vout[0].scriptPubKey = CScript() << CBigNum("0x5F1DF16B2B704C8A578D0BBAF74D385CDE12C11EE50455F3C438EF4C3FBCF649B6DE611FEAE06279A60939E028A8D65C10B73071A6F16719274855FEB0FD8A6704") << OP_CHECKSIG;
-        CBlock block;
-        block.vtx.push_back(txNew);
-        block.hashPrevBlock = 0;
-        block.hashMerkleRoot = block.BuildMerkleTree();
-        block.nVersion = 1;
-        // 1753315200 is 2025-07-24T00:00:00Z. The headline in pszTimestamp
-        // above reads 2026 and does not match it. This is a known discrepancy
-        // and not a typo in the constant: the value is only consensus-critical
-        // as an input to the genesis hash, the block hashes to
-        // hashGenesisBlock with it, and every node on the network agrees. The
-        // mismatch is in the launched chain and cannot be corrected -- see the
-        // warning above before deciding otherwise.
-        block.nTime    = 1753315200;
-        block.nBits    = 0x1f0fffff; // = bnProofOfWorkLimit (Bitflash RandomX floor)
-        block.nNonce   = GENESIS_NONCE;
+        // Upstream moved the construction into BuildGenesisBlock() so mainnet
+        // and the isolated testnet can share it. The mainnet inputs it uses are
+        // byte-identical to what this block built inline before the merge --
+        // timestamp string, nTime, nNonce, scriptPubKey, nBits and nVersion all
+        // verified equal against MAINNET_GENESIS_* -- so the mainnet genesis
+        // hash is unchanged. The warning below is why that was checked rather
+        // than assumed, and it still applies to those constants:
+        //
+        // Do not change MAINNET_GENESIS_TIMESTAMP, the scriptPubKey,
+        // MAINNET_GENESIS_TIME or MAINNET_GENESIS_NONCE. They are the inputs to
+        // the genesis hash, and the genesis hash is consensus. Changing one on
+        // its own trips the assert below, which is loud and reverts cleanly;
+        // changing one and regenerating GENESIS_NONCE and hashGenesisBlock to
+        // match -- which is exactly what the re-mining branch below prints out
+        // and invites -- gives a node that starts without complaint, builds its
+        // own chain from height 0, and rejects every real peer as being on a
+        // different chain. That one fails silently, and the damage scales with
+        // how many people run the "fixed" build.
+        //
+        // MAINNET_GENESIS_TIME is 1753315200, which is 2025-07-24T00:00:00Z,
+        // while the headline in MAINNET_GENESIS_TIMESTAMP reads 2026 -- as does
+        // the comment upstream put on that constant, which is wrong about the
+        // year. This is a known discrepancy and not a typo in the value: it is
+        // only consensus-critical as an input to the genesis hash, the block
+        // hashes to hashGenesisBlock with it, and every node on the network
+        // agrees. The mismatch is in the launched chain and cannot be corrected
+        // -- see the warning above before deciding otherwise.
+        CBlock block = BuildGenesisBlock();
 
         // If the nonce has not been found yet, mine the genesis once (RandomX)
         // and print the values to be hardcoded in the constants above.
diff --git a/src/main.h b/src/main.h
index e05b467..26b3b69 100644
--- a/src/main.h
+++ b/src/main.h
@@ -94,6 +94,8 @@ extern map<uint256, CBlockIndex*> mapBlockIndex;
 extern uint256 hashGenesisBlock;
 extern uint256 hashGenesisMerkleRoot;
 extern unsigned int GENESIS_NONCE;
+void SelectGenesisParams(bool fTestNetIn);
+void SelectChainParams(bool fTestNetIn);
 extern CBlockIndex* pindexGenesisBlock;
 extern int nBestHeight;
 extern uint256 hashBestChain;
diff --git a/src/main_gui.cpp b/src/main_gui.cpp
index dd001c8..2e4eb91 100644
--- a/src/main_gui.cpp
+++ b/src/main_gui.cpp
@@ -120,7 +120,7 @@ static void PrintUsage()
     printf("            wallet-crypto, wallet-encrypt, wallet-portability,\n");
     printf("            net-message,\n");
     printf("            consensus-limits, pool-stratum,\n");
-    printf("            parse-money, socks5-proxy, or managed-tor\n");
+    printf("            parse-money, network-params, socks5-proxy, or managed-tor\n");
     printf("\n");
     printf("Mining mode:\n");
     printf("  /operator\n");
@@ -132,6 +132,8 @@ static void PrintUsage()
     printf("  /stratumbridgeport=N       (default 3333; listen on 127.0.0.1)\n");
     printf("  /solomine\n");
     printf("  /genproclimit=N            (mining threads; 0 or absent = every core but one)\n");
+    printf("  /nolargepages              (do not ask for 2 MB pages for the RandomX\n");
+    printf("                              cache, dataset and scratchpads)\n");
     printf("  /checkblocks=N             (blocks re-verified at startup, default 288, 0 = all)\n");
     printf("\n");
     printf("Pool operator announcement:\n");
@@ -148,7 +150,8 @@ static void PrintUsage()
     printf("  /onionservice=HOST.onion:PORT  (advertise this node's Tor hidden service)\n");
     printf("\n");
     printf("Network:\n");
-    printf("  /port=N                    (P2P listen port, default 8433)\n");
+    printf("  /testnet                   (isolated test network genesis, datadir, port, and magic)\n");
+    printf("  /port=N                    (P2P listen port, default 8433; testnet 18433)\n");
     printf("  /socks=HOST:PORT           (SOCKS5 proxy for Nostr, .btf relay, and onion dials)\n");
     printf("  /tor[=HOST:PORT]           (Tor mode; default SOCKS5 proxy is 127.0.0.1:9050)\n");
     printf("  /managedtor[=PATH]         (start Tor, create a hidden service, advertise its onion)\n");
@@ -214,6 +217,9 @@ static void ParseStartupArguments(int argc, char* argv[])
     if (arg(argc,argv,"/datadir") || arg(argc,argv,"-datadir"))
         strSetDataDir = argval2(argc, argv, "/datadir", "-datadir");
 
+    bool fUseTestNet = arg(argc, argv, "/testnet") || arg(argc, argv, "-testnet");
+    SelectChainParams(fUseTestNet);
+
     if (arg(argc,argv,"/debug") || arg(argc,argv,"-debug"))
         fDebug = true;
 
@@ -284,6 +290,11 @@ static void ParseStartupArguments(int argc, char* argv[])
     if (!strCheckBlocks.empty())
         nCheckBlocksOnLoad = atoi(strCheckBlocks.c_str());
 
+    // Must be read before LoadBlockIndex(), which is what first calls
+    // RandomXInit() and fixes how the cache is allocated.
+    if (arg(argc,argv,"/nolargepages") || arg(argc,argv,"-nolargepages"))
+        fRandomXLargePages = false;
+
     // /genproclimit=N -- threads to hash with. 0 or absent means automatic,
     // which is every core but one. Named after Bitcoin's own option so it reads
     // familiarly to anyone who has run one of these before.
diff --git a/src/makefile.mingw b/src/makefile.mingw
index 740bba6..362794a 100644
--- a/src/makefile.mingw
+++ b/src/makefile.mingw
@@ -116,6 +116,7 @@ tests: test_bip32.exe bitflash.exe
         ./bitflash.exe -selftest=wallet-backend-default
         ./bitflash.exe -selftest=wallet-convert
         ./bitflash.exe -selftest=net-message
+        ./bitflash.exe -selftest=network-params
         ./bitflash.exe -selftest=consensus-limits
         ./bitflash.exe -selftest=pool-stratum
         ./bitflash.exe -selftest=socks5-proxy
diff --git a/src/net.cpp b/src/net.cpp
index bb05259..0576402 100644
--- a/src/net.cpp
+++ b/src/net.cpp
@@ -50,10 +50,14 @@ static int BtfPoll(BtfPollFd* pfd, unsigned int nfd, int nTimeoutMs)
 //
 // Global state variables
 //
+static const char pchMainnetMessageStart[4] = { 0xbf, 0x20, 0x5c, 0xfd };
+static const char pchTestnetMessageStart[4] = { (char)0xce, (char)0xe2, (char)0xc0, (char)0xff };
+static bool fTestNet = false;
+char pchMessageStart[4] = { 0xbf, 0x20, 0x5c, 0xfd };
 bool fClient = false;
 uint64 nLocalServices = (fClient ? 0 : NODE_NETWORK);
-CAddress addrLocalHost(0, DEFAULT_PORT, nLocalServices);
-unsigned short nListenPort = DEFAULT_PORT; // local P2P port (tunable via /port)
+CAddress addrLocalHost(0, GetDefaultPort(), nLocalServices);
+unsigned short nListenPort = GetDefaultPort(); // local P2P port (tunable via /port)
 CNode nodeLocalHost(INVALID_SOCKET, CAddress("127.0.0.1", nLocalServices));
 CNode* pnodeLocalHost = &nodeLocalHost;
 bool fShutdown = false;
@@ -90,6 +94,29 @@ static int64 nBtfHandshakeSilent = 0;
 static string strBtfLastDialFail;
 static string strBtfLastHandshakeTimeout;
 
+bool IsTestNet()
+{
+    return fTestNet;
+}
+
+unsigned short GetDefaultPort()
+{
+    return htons(fTestNet ? TESTNET_PORT : MAINNET_PORT);
+}
+
+void SelectNetworkParams(bool fTestNetIn)
+{
+    if (fTestNet == fTestNetIn)
+        return;
+
+    fTestNet = fTestNetIn;
+    memcpy(pchMessageStart,
+           fTestNet ? pchTestnetMessageStart : pchMainnetMessageStart,
+           sizeof(pchMessageStart));
+    nListenPort = GetDefaultPort();
+    addrLocalHost.port = nListenPort;
+}
+
 void BtfChurnNoteResolveAttempt()
 {
     CRITICAL_BLOCK(cs_btfChurn)
@@ -288,6 +315,7 @@ string GetDiagnosticsText()
     int nMedian = GetPeerMedianHeight();
 
     str += "Bitflash node diagnostics\n";
+    str += strprintf("  network           %s\n", IsTestNet() ? "testnet" : "mainnet");
     str += strprintf("  uptime            %s\n",
                      FormatAge(nNodeStartTime ? nNow - nNodeStartTime : -1).c_str());
     if (nMedian < 0)
@@ -338,6 +366,7 @@ string GetDiagnosticsText()
                                      nMining,
                                      (RandomXFastReady() ? 2080 : 256) + 2 * nMining).c_str()
                          : ", not mining");
+    str += strprintf("  large pages       %s\n", RandomXLargePagesStatus());
 
     str += SockAccountingText();
 
diff --git a/src/net.h b/src/net.h
index 752b1fe..0988542 100644
--- a/src/net.h
+++ b/src/net.h
@@ -12,7 +12,13 @@ class CBlockIndex;
 
 
 
-static const unsigned short DEFAULT_PORT = htons(8433);
+// Held in host byte order, unlike the DEFAULT_PORT constant these replace,
+// which was htons(8433). Nothing is lost: net.cpp's GetDefaultPort() applies
+// htons() itself and is what every caller now uses, so the value that reaches
+// a sockaddr is byte-for-byte what it was. Mainnet stays on 8433.
+static const unsigned short MAINNET_PORT = 8433;
+static const unsigned short TESTNET_PORT = 18433;
+static const unsigned int PUBLISH_HOPS = 5;
 enum
 {
     NODE_NETWORK = (1 << 0),
@@ -30,6 +36,9 @@ enum
 bool IsBlockFetchNearTip();
 
 bool GetMyExternalIP(unsigned int& ipRet);
+bool IsTestNet();
+unsigned short GetDefaultPort();
+void SelectNetworkParams(bool fTestNetIn);
 CNode* ConnectNodeBtf(const string& strBtfAddr);
 CNode* ConnectNodeBtfResolved(const string& strBtfAddr, const string& strMeeting,
                               const string& strOnion, const unsigned char enc_pub[32],
@@ -266,15 +275,17 @@ void CheckForShutdown(int n);
 // The message start string is designed to be unlikely to occur in normal data.
 // The characters are rarely used upper ascii, not valid as UTF-8, and produce
 // a large 4-byte int at any alignment.
-// Magic bytes unique to the Bitflash network (0xbf = "BF"). Second byte bumped
-// to 0x20 for the 2026 stable relaunch so the old test chain can't interfere.
-static const char pchMessageStart[4] = { 0xbf, 0x20, 0x5c, 0xfd };
+// Magic bytes unique to the selected Bitflash network. Mainnet uses 0xbf =
+// "BF"; testnet swaps the whole sequence so a test node cannot handshake with
+// mainnet before consensus-level testnet activation exists.
+extern char pchMessageStart[4];
 
 class CMessageHeader
 {
 public:
     enum { COMMAND_SIZE=12 };
-    char pchMessageStart[sizeof(::pchMessageStart)];
+    enum { MESSAGE_START_SIZE=4 };
+    char pchMessageStart[MESSAGE_START_SIZE];
     char pchCommand[COMMAND_SIZE];
     unsigned int nMessageSize;
 
@@ -365,7 +376,7 @@ public:
         nServices = 0;
         memcpy(pchReserved, pchIPv4, sizeof(pchReserved));
         ip = 0;
-        port = DEFAULT_PORT;
+        port = GetDefaultPort();
         nTime = GetAdjustedTime();
         nLastFailed = 0;
     }
@@ -395,7 +406,7 @@ public:
         nServices = nServicesIn;
         memcpy(pchReserved, pchIPv4, sizeof(pchReserved));
         ip = 0;
-        port = DEFAULT_PORT;
+        port = GetDefaultPort();
         nTime = GetAdjustedTime();
         nLastFailed = 0;
 
diff --git a/src/randomx_pow.cpp b/src/randomx_pow.cpp
index 9c59364..a509543 100644
--- a/src/randomx_pow.cpp
+++ b/src/randomx_pow.cpp
@@ -24,6 +24,50 @@ static std::mutex      g_csInit;
 static bool            g_fInit    = false;
 static bool            g_fFast    = false;
 
+// RandomX reads a 256 MB cache, a 2 GB dataset and a 2 MB scratchpad per VM
+// at random, so most reads miss the TLB on 4 KB pages. 2 MB pages recover
+// roughly a tenth of the hash rate.
+//
+// The pool must be reserved first (vm.nr_hugepages), and RandomX returns NULL
+// instead of falling back, so each allocation below retries without the flag.
+bool fRandomXLargePages = true;   // cleared by -nolargepages
+static bool g_fLargeCache   = false;
+static bool g_fLargeDataset = false;
+static bool g_fLargeAny     = false;
+
+// How to reserve the large-page pool, for the hint printed when a large-page
+// allocation falls back to normal pages. The mechanism is OS-specific.
+static const char* LargePagesHint()
+{
+#ifdef _WIN32
+    return "enable the \"Lock pages in memory\" privilege and run elevated";
+#else
+    return "reserve them with: sysctl vm.nr_hugepages=1280";
+#endif
+}
+
+static randomx_flags WithLargePages(randomx_flags f)
+{
+    return (randomx_flags)(f | RANDOMX_FLAG_LARGE_PAGES);
+}
+
+// Ask for a cache in large pages, then plain pages. Sets fLargeOut to say
+// which one answered.
+static randomx_cache* AllocCache(randomx_flags flags, bool& fLargeOut)
+{
+    fLargeOut = false;
+    if (fRandomXLargePages)
+    {
+        randomx_cache* c = randomx_alloc_cache(WithLargePages(flags));
+        if (c)
+        {
+            fLargeOut = true;
+            return c;
+        }
+    }
+    return randomx_alloc_cache(flags);
+}
+
 
 bool RandomXInit()
 {
@@ -37,28 +81,56 @@ bool RandomXInit()
     // Detect the best flags for this CPU (JIT, hardware AES, Argon2).
     g_flags = randomx_get_flags();
 
-    g_cache = randomx_alloc_cache(g_flags);
+    g_cache = AllocCache(g_flags, g_fLargeCache);
     if (!g_cache)
     {
         // Try without JIT as a fallback
         g_flags = RANDOMX_FLAG_DEFAULT;
-        g_cache = randomx_alloc_cache(g_flags);
+        g_cache = AllocCache(g_flags, g_fLargeCache);
         if (!g_cache)
             return error("RandomX: failed to allocate cache (256 MB)");
     }
     randomx_init_cache(g_cache, RANDOMX_KEY, strlen(RANDOMX_KEY));
 
-    // Verification VM in light mode (cache only)
-    g_vmVerify = randomx_create_vm(g_flags, g_cache, NULL);
+    // Verification VM in light mode (cache only). The scratchpad is only 2 MB
+    // and this VM is created once, but it hashes every block the node ever
+    // validates, so it gets the same treatment.
+    bool fLargeVerify = false;
+    if (fRandomXLargePages)
+    {
+        g_vmVerify = randomx_create_vm(WithLargePages(g_flags), g_cache, NULL);
+        fLargeVerify = (g_vmVerify != NULL);
+    }
+    if (!g_vmVerify)
+        g_vmVerify = randomx_create_vm(g_flags, g_cache, NULL);
     if (!g_vmVerify)
         return error("RandomX: failed to create verification VM");
 
+    g_fLargeAny = g_fLargeCache || fLargeVerify;
     g_fInit = true;
-    printf("RandomX: initialized (cache 256 MB, flags=%d)\n", (int)g_flags);
+    printf("RandomX: initialized (cache 256 MB, flags=%d, large pages: %s)\n",
+           (int)g_flags, RandomXLargePagesStatus());
+    if (fRandomXLargePages && !g_fLargeCache)
+        printf("RandomX: large pages unavailable for the cache; %s "
+               "for about 10%% more hash rate\n", LargePagesHint());
     return true;
 }
 
 
+const char* RandomXLargePagesStatus()
+{
+    if (!fRandomXLargePages)
+        return "off (-nolargepages)";
+    if (g_fLargeCache && g_fLargeDataset)
+        return "cache + dataset";
+    if (g_fLargeCache)
+        return "cache only";
+    if (g_fLargeDataset)
+        return "dataset only";
+    return g_fLargeAny ? "scratchpad only" : "unavailable";
+}
+
+
 // One dataset, once, no matter how many miners ask for it.
 //
 // Every miner thread calls this at startup. The g_fFast guard below is only
@@ -88,8 +160,18 @@ bool RandomXInitDataset(int nThreads)
     if (g_fFast)
         return true;
 
-    randomx_flags fastFlags = (randomx_flags)(g_flags | RANDOMX_FLAG_FULL_MEM);
-    g_dataset = randomx_alloc_dataset(fastFlags);
+    // Only RANDOMX_FLAG_LARGE_PAGES means anything to randomx_alloc_dataset;
+    // the rest of g_flags belongs to the VMs that read it.
+    if (fRandomXLargePages)
+    {
+        g_dataset = randomx_alloc_dataset(WithLargePages(RANDOMX_FLAG_DEFAULT));
+        g_fLargeDataset = (g_dataset != NULL);
+        if (!g_dataset)
+            printf("RandomX: large pages unavailable for the 2 GB dataset; %s "
+                   "for about 10%% more hash rate\n", LargePagesHint());
+    }
+    if (!g_dataset)
+        g_dataset = randomx_alloc_dataset(RANDOMX_FLAG_DEFAULT);
     if (!g_dataset)
     {
         printf("RandomX: not enough memory for the 2 GB dataset, staying in light mode\n");
@@ -158,13 +240,26 @@ void* RandomXCreateMinerVM()
 {
     if (!g_fInit && !RandomXInit())
         return NULL;
+
+    randomx_flags   flags   = g_flags;
+    randomx_cache*  cache   = g_cache;
+    randomx_dataset* dataset = NULL;
     if (g_fFast && g_dataset)
     {
-        randomx_flags fastFlags = (randomx_flags)(g_flags | RANDOMX_FLAG_FULL_MEM);
-        return randomx_create_vm(fastFlags, NULL, g_dataset);
+        flags   = (randomx_flags)(g_flags | RANDOMX_FLAG_FULL_MEM);
+        cache   = NULL;
+        dataset = g_dataset;
+    }
+
+    // Each thread gets its own 2 MB scratchpad, so the large-page pool can run
+    // dry partway through a fleet of miners. Threads that miss out still run.
+    if (fRandomXLargePages)
+    {
+        randomx_vm* vm = randomx_create_vm(WithLargePages(flags), cache, dataset);
+        if (vm)
+            return vm;
     }
-    // Light mode: own VM sharing the cache
-    return randomx_create_vm(g_flags, g_cache, NULL);
+    return randomx_create_vm(flags, cache, dataset);
 }
 
 
diff --git a/src/randomx_pow.h b/src/randomx_pow.h
index 0027571..355b708 100644
--- a/src/randomx_pow.h
+++ b/src/randomx_pow.h
@@ -41,4 +41,11 @@ uint256 RandomXHashWithVM(void* vm, const void* pHeader, size_t nSize);
 // True when the 2 GB dataset is ready (fast mode active).
 bool RandomXFastReady();
 
+// Ask for large (2 MB) pages for the cache, dataset and scratchpads. Set false
+// by -nolargepages. Must be set before the first RandomXInit().
+extern bool fRandomXLargePages;
+
+// Which allocations actually got large pages, for the status display.
+const char* RandomXLargePagesStatus();
+
 #endif
diff --git a/src/readme.txt b/src/readme.txt
index 7490a9a..455884c 100644
--- a/src/readme.txt
+++ b/src/readme.txt
@@ -41,7 +41,8 @@ The resulting executable is src/bitflash.exe.
 
 Command-line options (in addition to the original ones)
 -------------------------------------------------------
-  /port=N        listen on P2P port N (default 8433)
+  /testnet       use isolated test network genesis, datadir, port 18433, and message magic
+  /port=N        listen on P2P port N (default 8433; testnet default 18433)
   /socks=HOST:PORT
                  route outbound Nostr, .btf rendezvous, and direct onion peer
                  dials through a SOCKS5 proxy, e.g. /socks=127.0.0.1:9050 for local Tor
diff --git a/src/selftest.cpp b/src/selftest.cpp
index 65f215b..357d532 100644
--- a/src/selftest.cpp
+++ b/src/selftest.cpp
@@ -3118,6 +3118,87 @@ static int RunNetMessageSelfTest()
     return nFail == 0 ? 0 : 1;
 }
 
+static int RunNetworkParamsSelfTest()
+{
+    fflush(stdout);
+    printf("network-params self-test\n");
+
+    int nFail = 0;
+    std::string strOldDataDir = strSetDataDir;
+    try
+    {
+        SelectChainParams(false);
+        nFail += Check(!IsTestNet(), "starts on mainnet after explicit selection") ? 0 : 1;
+        nFail += Check(ntohs(GetDefaultPort()) == MAINNET_PORT,
+                       "mainnet default P2P port is 8433") ? 0 : 1;
+        CAddress mainAddr("127.0.0.1");
+        nFail += Check(mainAddr.port == htons(MAINNET_PORT),
+                       "mainnet address parsing uses the mainnet default port") ? 0 : 1;
+        CMessageHeader mainHeader("ping", 0);
+        char mainMagic[4];
+        memcpy(mainMagic, mainHeader.pchMessageStart, sizeof(mainMagic));
+        uint256 mainGenesis = hashGenesisBlock;
+        uint256 mainMerkle = hashGenesisMerkleRoot;
+        unsigned int mainNonce = GENESIS_NONCE;
+
+        SelectChainParams(true);
+        nFail += Check(IsTestNet(), "testnet selection is sticky") ? 0 : 1;
+        nFail += Check(ntohs(GetDefaultPort()) == TESTNET_PORT,
+                       "testnet default P2P port is 18433") ? 0 : 1;
+        CAddress testAddr("127.0.0.1");
+        nFail += Check(testAddr.port == htons(TESTNET_PORT),
+                       "testnet address parsing uses the testnet default port") ? 0 : 1;
+        CMessageHeader testHeader("ping", 0);
+        nFail += Check(memcmp(mainMagic, testHeader.pchMessageStart, sizeof(mainMagic)) != 0,
+                       "testnet message magic differs from mainnet") ? 0 : 1;
+        nFail += Check(hashGenesisBlock != mainGenesis &&
+                       hashGenesisMerkleRoot != mainMerkle &&
+                       GENESIS_NONCE != mainNonce,
+                       "testnet genesis constants differ from mainnet") ? 0 : 1;
+        nFail += Check(hashGenesisBlock == uint256("0xa9d11c6d697bcb7aea0653bc088b12dcf9f44e732df205162cf085fd9d9963eb") &&
+                       hashGenesisMerkleRoot == uint256("0x510b293105e3ff85b8d4c3920e357f85d1a86bf199eb4e7d11f04f380030ec5c") &&
+                       GENESIS_NONCE == 3199,
+                       "testnet genesis constants are pinned") ? 0 : 1;
+
+        std::string tmp;
+        if (!MakeTempDir(tmp))
+        {
+            nFail += Check(false, "creates a temporary data directory") ? 0 : 1;
+        }
+        else
+        {
+            strSetDataDir = tmp;
+            SelectChainParams(false);
+            std::string mainDir = GetAppDir();
+            SelectChainParams(true);
+            std::string testDir = GetAppDir();
+            nFail += Check(mainDir == tmp,
+                           "mainnet uses the selected data directory") ? 0 : 1;
+            nFail += Check(testDir == tmp + "/testnet",
+                           "testnet stores data below a testnet subdirectory") ? 0 : 1;
+            RemoveTree(tmp);
+        }
+    }
+    catch (const std::exception& e)
+    {
+        printf("  FAIL exception: %s\n", e.what());
+        nFail++;
+    }
+    catch (...)
+    {
+        printf("  FAIL unknown exception\n");
+        nFail++;
+    }
+
+    strSetDataDir = strOldDataDir;
+    SelectChainParams(false);
+
+    printf("%s (%d failure%s)\n", nFail == 0 ? "ALL TESTS PASSED" : "TESTS FAILED",
+           nFail, nFail == 1 ? "" : "s");
+    fflush(stdout);
+    return nFail == 0 ? 0 : 1;
+}
+
 static CBlock MakeSizedConsensusBlock(size_t nScriptBytes)
 {
     CTransaction tx;
@@ -3716,6 +3797,8 @@ int RunSelfTest(const std::string& name)
         return RunWalletPortabilitySelfTest();
     if (name == "net-message")
         return RunNetMessageSelfTest();
+    if (name == "network-params")
+        return RunNetworkParamsSelfTest();
     if (name == "consensus-limits")
         return RunConsensusLimitsSelfTest();
     if (name == "pool-stratum")
@@ -3730,6 +3813,6 @@ int RunSelfTest(const std::string& name)
         return RunManagedTorSelfTest();
 
     printf("Unknown self-test '%s'\n", name.c_str());
-    printf("Known self-tests: wallet-keypool, wallet-hd, wallet-format, wallet-storage-sanity, db-env-reopen, wallet-sqlite, wallet-sqlite-migration, wallet-crypto, wallet-encrypt, wallet-sqlite-encrypt, wallet-backend-default, wallet-convert, wallet-portability, net-message, consensus-limits, pool-stratum, payout-ledger, parse-money, socks5-proxy, managed-tor\n");
+    printf("Known self-tests: wallet-keypool, wallet-hd, wallet-format, wallet-storage-sanity, db-env-reopen, wallet-sqlite, wallet-sqlite-migration, wallet-crypto, wallet-encrypt, wallet-sqlite-encrypt, wallet-backend-default, wallet-convert, wallet-portability, net-message, network-params, consensus-limits, pool-stratum, payout-ledger, parse-money, socks5-proxy, managed-tor\n");
     return 1;
 }