From 160fcc657a4fd8108c250fcf610c3631787796e2 Mon Sep 17 00:00:00 2001
From: morgan <mc@m-labs.hk>
Date: Fri, 2 Aug 2024 12:35:19 +0800
Subject: [PATCH] cxp downconn: remove bruteforce aligner

---
 src/gateware/cxp_downconn.py | 118 -----------------------------------
 1 file changed, 118 deletions(-)

diff --git a/src/gateware/cxp_downconn.py b/src/gateware/cxp_downconn.py
index bd83ba6..8750f4c 100644
--- a/src/gateware/cxp_downconn.py
+++ b/src/gateware/cxp_downconn.py
@@ -1,6 +1,5 @@
 from migen import *
 from migen.genlib.resetsync import AsyncResetSynchronizer
-from migen.genlib.cdc import MultiReg, PulseSynchronizer
 
 from misoc.cores.code_8b10b import Encoder, Decoder
 from misoc.interconnect.csr import *
@@ -254,111 +253,6 @@ class QPLL(Module):
             )
         ]
 
-# Changes the phase of the transceiver RX clock to align the comma to
-# the LSBs of RXDATA, fixing the latency.
-#
-# This is implemented by repeatedly resetting the transceiver until it
-# gives out the correct phase. Each reset gives a random phase.
-#
-# If Xilinx had designed the GTX transceiver correctly, RXSLIDE_MODE=PMA
-# would achieve this faster and in a cleaner way. But:
-#  * the phase jumps are of 2 UI at every second RXSLIDE pulse, instead
-#    of 1 UI at every pulse. It is unclear what the latency becomes.
-#  * RXSLIDE_MODE=PMA cannot be used with the RX buffer bypassed.
-# Those design flaws make RXSLIDE_MODE=PMA yet another broken and useless
-# transceiver "feature".
-#
-# Warning: Xilinx transceivers are LSB first, and comma needs to be flipped
-# compared to the usual 8b10b binary representation.
-class CXP_BruteforceClockAligner(Module):
-    def __init__(self, comma, check_max_val):
-        self.rxdata = Signal(20)
-        self.restart = Signal()
-
-        self.ready = Signal()
-
-        check_counter = Signal(max=check_max_val+1)
-        check = Signal()
-        reset_check_counter = Signal()
-        self.sync.cxp_gtx_tx += [
-            check.eq(0),
-            If(reset_check_counter,
-                check_counter.eq(check_max_val)
-            ).Else(
-                If(check_counter == 0,
-                    check.eq(1),
-                    check_counter.eq(check_max_val)
-                ).Else(
-                    check_counter.eq(check_counter-1)
-                )
-            )
-        ]
-
-        checks_reset = PulseSynchronizer("cxp_gtx_tx", "cxp_gtx_rx")
-        self.submodules += checks_reset
-
-        comma_n = ~comma & 0b1111111111
-        comma_seen_rxclk = Signal()
-        comma_seen = Signal()
-        comma_seen_rxclk.attr.add("no_retiming")
-        self.specials += MultiReg(comma_seen_rxclk, comma_seen)
-        self.sync.cxp_gtx_rx += \
-            If(checks_reset.o,
-                comma_seen_rxclk.eq(0)
-            ).Elif((self.rxdata[:10] == comma) | (self.rxdata[:10] == comma_n),
-                comma_seen_rxclk.eq(1)
-            )
-
-        error_seen_rxclk = Signal()
-        error_seen = Signal()
-        error_seen_rxclk.attr.add("no_retiming")
-        self.specials += MultiReg(error_seen_rxclk, error_seen)
-        rx1cnt = Signal(max=11)
-        self.sync.cxp_gtx_rx += [
-            rx1cnt.eq(reduce(add, [self.rxdata[i] for i in range(10)])),
-            If(checks_reset.o,
-                error_seen_rxclk.eq(0)
-            ).Elif((rx1cnt != 4) & (rx1cnt != 5) & (rx1cnt != 6),
-                error_seen_rxclk.eq(1)
-            )
-        ]
-
-        fsm = ClockDomainsRenamer("cxp_gtx_tx")(FSM(reset_state="WAIT_COMMA"))
-        self.submodules += fsm
-
-        fsm.act("WAIT_COMMA",
-            If(check,
-                # Errors are still OK at this stage, as the transceiver
-                # has just been reset and may output garbage data.
-                If(comma_seen,
-                    NextState("WAIT_NOERROR")
-                ).Else(
-                    self.restart.eq(1)
-                ),
-                checks_reset.i.eq(1)
-            )
-        )
-        fsm.act("WAIT_NOERROR",
-            If(check,
-                If(comma_seen & ~error_seen,
-                    NextState("READY")
-                ).Else(
-                    self.restart.eq(1),
-                    NextState("WAIT_COMMA")
-                ),
-                checks_reset.i.eq(1)
-            )
-        )
-        fsm.act("READY",
-            reset_check_counter.eq(1),
-            self.ready.eq(1),
-            If(error_seen,
-                checks_reset.i.eq(1),
-                self.restart.eq(1),
-                NextState("WAIT_COMMA")
-            )
-        )
-
 # Warning: Xilinx transceivers are LSB first, and comma needs to be flipped
 # compared to the usual 8b10b binary representation.
 class Manual_Aligner(Module):
@@ -753,20 +647,8 @@ class GTX(Module):
             self.decoders[1].input.eq(rxdata[10:])
         ]
 
-        # 62.5MHz: cannot align
-        # 125MHz: align <1s
-        # 156.25MHz: align <15s
-        # 250MHz: cannot align
-        # clock_aligner = CXP_BruteforceClockAligner(0b0101111100, 1_000_000)
-        # self.submodules += clock_aligner
-        # self.comb += [
-        #     clock_aligner.rxdata.eq(rxdata),
-        #     rx_init.restart.eq(clock_aligner.restart),
-        #     self.rx_ready.eq(clock_aligner.ready),
-        # ]
 
         self.submodules.clk_aligner = clk_aligner = Manual_Aligner(0b0101111100)
-        
         self.comb += [
             clk_aligner.rxdata.eq(rxdata),
             rxslide.eq(clk_aligner.rxslide),