drtio: more reliable link layer init

artiq/gateware/drtio/core.py

@@ -6,9 +6,10 @@ from artiq.gateware.drtio import link_layer, rt_packets, iot, rt_controller
 
 
 class DRTIOSatellite(Module):
-    def __init__(self, transceiver, rx_synchronizer, channels, fine_ts_width=3, full_ts_width=63):
+    def __init__(self, transceiver, rx_synchronizer, channels, fine_ts_width=3, full_ts_width=63,
+                 ll_rx_ready_confirm=1000):
         self.submodules.link_layer = link_layer.LinkLayer(
-            transceiver.encoder, transceiver.decoders)
+            transceiver.encoder, transceiver.decoders, ll_rx_ready_confirm)
         self.comb += [
             transceiver.rx_reset.eq(self.link_layer.rx_reset),
             self.link_layer.rx_ready.eq(transceiver.rx_ready)
@@ -45,9 +46,9 @@ class DRTIOSatellite(Module):
 
 
 class DRTIOMaster(Module):
-    def __init__(self, transceiver, channel_count=1024, fine_ts_width=3):
+    def __init__(self, transceiver, channel_count=1024, fine_ts_width=3, ll_rx_ready_confirm=1000):
         self.submodules.link_layer = link_layer.LinkLayer(
-            transceiver.encoder, transceiver.decoders)
+            transceiver.encoder, transceiver.decoders, ll_rx_ready_confirm)
         self.comb += [
             transceiver.rx_reset.eq(self.link_layer.rx_reset),
             self.link_layer.rx_ready.eq(transceiver.rx_ready)

artiq/gateware/drtio/link_layer.py

@@ -4,6 +4,7 @@ from operator import xor, or_
 from migen import *
 from migen.genlib.fsm import *
 from migen.genlib.cdc import MultiReg, BusSynchronizer
+from migen.genlib.misc import WaitTimer
 
 from misoc.interconnect.csr import *
 
@@ -212,7 +213,7 @@ class LinkLayerRX(Module):
 
 
 class LinkLayer(Module, AutoCSR):
-    def __init__(self, encoder, decoders):
+    def __init__(self, encoder, decoders, rx_ready_confirm_cycles):
         self.link_status = CSRStatus(3)
 
         # control signals, in rtio clock domain
@@ -272,6 +273,12 @@ class LinkLayer(Module, AutoCSR):
         self.submodules += link_status
         self.comb += self.link_status.status.eq(link_status.o)
 
+        wait_confirm = ClockDomainsRenamer("rtio")(
+            WaitTimer(rx_ready_confirm_cycles))
+        self.submodules += wait_confirm
+        signal_rx_ready_margin = ClockDomainsRenamer("rtio")(WaitTimer(15))
+        self.submodules += signal_rx_ready_margin
+
         fsm.act("RESET_RX",
             link_status.i.eq(0),
             tx.link_init.eq(1),
@@ -281,24 +288,40 @@ class LinkLayer(Module, AutoCSR):
         fsm.act("WAIT_LOCAL_RX_READY",
             link_status.i.eq(1),
             tx.link_init.eq(1),
-            If(self.rx_ready,
-                NextState("WAIT_REMOTE_RX_READY")
-            )
+            If(self.rx_ready, NextState("CONFIRM_LOCAL_RX_READY"))
         )
-        fsm.act("WAIT_REMOTE_RX_READY",
+        fsm.act("CONFIRM_LOCAL_RX_READY",
             link_status.i.eq(2),
             tx.link_init.eq(1),
+            wait_confirm.wait.eq(1),
+            If(wait_confirm.done, NextState("WAIT_REMOTE_RX_READY")),
+            If(~rx_link_init, NextState("RESET_RX"))
+        )
+        fsm.act("WAIT_REMOTE_RX_READY",
+            link_status.i.eq(3),
+            tx.link_init.eq(1),
             tx.signal_rx_ready.eq(1),
-            If(rx_remote_rx_ready,
-                NextState("WAIT_REMOTE_LINK_UP")
-            )
+            If(rx_remote_rx_ready, NextState("ENSURE_SIGNAL_RX_READY"))
+        )
+        # If the transceiver transmits one character per RTIO cycle,
+        # we may be unlucky and signal_rx_ready will transmit a comma
+        # on the first cycle instead of a "RX ready" character.
+        # Further, we need to ensure the rx.remote_rx_ready
+        # gets through MultiReg to rx_remote_rx_ready at the receiver.
+        # So transmit the "RX ready" pattern for several cycles.
+        fsm.act("ENSURE_SIGNAL_RX_READY",
+            link_status.i.eq(3),
+            tx.link_init.eq(1),
+            tx.signal_rx_ready.eq(1),
+            signal_rx_ready_margin.wait.eq(1),
+            If(signal_rx_ready_margin.done, NextState("WAIT_REMOTE_LINK_UP"))
         )
         fsm.act("WAIT_REMOTE_LINK_UP",
-            link_status.i.eq(3),
+            link_status.i.eq(4),
             If(~rx_link_init, NextState("READY"))
         )
         fsm.act("READY",
-            link_status.i.eq(4),
-            If(rx_link_init, NextState("RESET_RX")),
+            link_status.i.eq(5),
+            If(rx_link_init, NextState("RESET_RX")),  # TODO: remove this, link deinit should be detected at upper layer
             self.ready.eq(1)
         )

artiq/runtime.rs/src/drtio.rs

@@ -3,7 +3,7 @@ use sched::{Waiter, Spawner};
 
 fn drtio_link_is_up() -> bool {
     unsafe {
-        csr::drtio::link_status_read() == 4
+        csr::drtio::link_status_read() == 5
     }
 }
 

artiq/test/gateware/drtio/test_full_stack.py

@@ -41,7 +41,8 @@ class DUT(Module):
         self.ttl1 = Signal()
         self.transceivers = DummyTransceiverPair(nwords)
         
-        self.submodules.master = DRTIOMaster(self.transceivers.alice)
+        self.submodules.master = DRTIOMaster(self.transceivers.alice,
+                                             ll_rx_ready_confirm=15)
 
         rx_synchronizer = DummyRXSynchronizer()
         self.submodules.phy0 = ttl_simple.Output(self.ttl0)
@@ -51,7 +52,8 @@ class DUT(Module):
             rtio.Channel.from_phy(self.phy1, ofifo_depth=4)
         ]
         self.submodules.satellite = DRTIOSatellite(
-            self.transceivers.bob, rx_synchronizer, rtio_channels)
+            self.transceivers.bob, rx_synchronizer, rtio_channels,
+            ll_rx_ready_confirm=15)
         
 
 class TestFullStack(unittest.TestCase):