diff --git a/misoclib/com/liteeth/phy/gmii_mii.py b/misoclib/com/liteeth/phy/gmii_mii.py
index 5cf8669d6..91a122d5f 100644
--- a/misoclib/com/liteeth/phy/gmii_mii.py
+++ b/misoclib/com/liteeth/phy/gmii_mii.py
@@ -1,10 +1,11 @@
 from migen.genlib.io import DDROutput
 from migen.flow.plumbing import Multiplexer, Demultiplexer
+from migen.genlib.cdc import MultiReg
 
 from misoclib.com.liteeth.common import *
 from misoclib.com.liteeth.generic import *
 
-from misoclib.com.liteeth.phy.gmii import LiteEthPHYGMIIMIICRG
+from misoclib.com.liteeth.phy.gmii import LiteEthPHYGMIICRG
 from misoclib.com.liteeth.phy.mii import LiteEthPHYMIITX, LiteEthPHYMIIRX
 from misoclib.com.liteeth.phy.gmii import LiteEthPHYGMIITX, LiteEthPHYGMIIRX
 
@@ -67,6 +68,19 @@ class LiteEthPHYGMIIMIIRX(Module):
 			Record.connect(mux.source, source)
 		]
 
+class LiteEthGMIIMIIClockCounter(Module, AutoCSR):
+	def __init__(self):
+		self._reset = CSRStorage()
+		self._value = CSRStatus(32)
+		###
+		counter = RenameClockDomains(Counter(32), "eth_rx")
+		self.submodules += counter
+		self.comb += [
+			counter.reset.eq(self._reset.storage), #slow, don't need CDC
+			counter.ce.eq(1),
+		]
+		self.specials += MultiReg(counter.value, self._value.status)
+
 class LiteEthPHYGMIIMII(Module, AutoCSR):
 	def __init__(self, clock_pads, pads, with_hw_init_reset=True):
 		self.dw = 8
@@ -74,6 +88,7 @@ class LiteEthPHYGMIIMII(Module, AutoCSR):
 		mode = self._mode.storage
 		# Note: we can use GMII CRG since it also handles tx clock pad used for MII
 		self.submodules.crg = LiteEthPHYGMIICRG(clock_pads, pads, with_hw_init_reset)
+		self.submodules.clock_counter = LiteEthGMIIMIIClockCounter()
 		self.submodules.tx = RenameClockDomains(LiteEthPHYGMIIMIITX(pads, mode), "eth_tx")
 		self.submodules.rx = RenameClockDomains(LiteEthPHYGMIIMIIRX(pads, mode), "eth_rx")
 		self.sink, self.source = self.tx.sink, self.rx.source
diff --git a/software/bios/main.c b/software/bios/main.c
index 5c92b93e8..28f79dfc8 100644
--- a/software/bios/main.c
+++ b/software/bios/main.c
@@ -502,6 +502,9 @@ static void boot_sequence(void)
 		flashboot();
 #endif
 		serialboot();
+#ifdef CSR_ETHPHY_MODE_ADDR
+		ethmode();
+#endif
 #ifdef CSR_ETHMAC_BASE
 		netboot();
 #endif
diff --git a/software/include/net/microudp.h b/software/include/net/microudp.h
index f9b339800..15c2a47dc 100644
--- a/software/include/net/microudp.h
+++ b/software/include/net/microudp.h
@@ -15,5 +15,6 @@ void microudp_set_callback(udp_callback callback);
 void microudp_service(void);
 
 void ethreset(void);
+void ethmode(void);
 
 #endif /* __MICROUDP_H */
diff --git a/software/libnet/microudp.c b/software/libnet/microudp.c
index 8720407e1..2e6bceb23 100644
--- a/software/libnet/microudp.c
+++ b/software/libnet/microudp.c
@@ -444,4 +444,27 @@ void ethreset(void)
 	busy_wait(2);
 }
 
+void ethmode(void)
+{
+	ethphy_clock_counter_reset_write(1);
+	busy_wait(1);
+	ethphy_clock_counter_reset_write(0);
+	busy_wait(1);
+
+	printf("Ethernet phy mode: ");
+	/* if freq > 120 MHz, use GMII (5MHz margin)*/
+	if (ethphy_clock_counter_value_read() > 120000000/10) {
+		ethphy_mode_write(0);
+		printf("GMII");
+	/* else use MII */
+	} else {
+		ethphy_mode_write(1);
+		printf("MII");
+	}
+	printf("\n");
+
+	ethphy_clock_counter_reset_write(1);
+}
+
 #endif
+