From 67bfb947f43a218a4c820b0e588cebed66e8d1b8 Mon Sep 17 00:00:00 2001
From: Alex Forencich <alex@alexforencich.com>
Date: Wed, 6 Aug 2025 15:09:04 -0700
Subject: [PATCH] zircon: Add TX buffer module

Signed-off-by: Alex Forencich <alex@alexforencich.com>
---
 src/zircon/rtl/zircon_ip_tx_buffer.sv | 135 ++++++++++++++++++++++++++
 1 file changed, 135 insertions(+)
 create mode 100644 src/zircon/rtl/zircon_ip_tx_buffer.sv

diff --git a/src/zircon/rtl/zircon_ip_tx_buffer.sv b/src/zircon/rtl/zircon_ip_tx_buffer.sv
new file mode 100644
index 0000000..8462871
--- /dev/null
+++ b/src/zircon/rtl/zircon_ip_tx_buffer.sv
@@ -0,0 +1,135 @@
+// SPDX-License-Identifier: CERN-OHL-S-2.0
+/*
+
+Copyright (c) 2025 FPGA Ninja, LLC
+
+Authors:
+- Alex Forencich
+
+*/
+
+`resetall
+`timescale 1ns / 1ps
+`default_nettype none
+
+/*
+ * Zircon IP stack - TX packet buffer
+ */
+module zircon_ip_tx_buffer #
+(
+    parameter N_UI = 4,
+    parameter TX_RAM_SIZE = 32768
+)
+(
+    input  wire logic  clk,
+    input  wire logic  rst,
+
+    /*
+     * Packet data input
+     */
+    taxi_axis_if.snk   s_axis_pkt_ui[N_UI],
+
+    /*
+     * Metadata output
+     */
+    taxi_axis_if.src   m_axis_meta_len,
+
+    /*
+     * Transfer command input and packet data output
+     */
+    taxi_axis_if.src   m_axis_pkt
+);
+
+localparam DATA_W = m_axis_pkt.DATA_W;
+localparam TX_USER_W = m_axis_pkt.USER_W;
+localparam TX_TAG_W = m_axis_pkt.ID_W;
+
+taxi_axis_if #(.DATA_W(DATA_W), .USER_EN(1), .USER_W(TX_USER_W), .ID_EN(1), .ID_W(TX_TAG_W)) axis_pkt_1();
+taxi_axis_if #(.DATA_W(DATA_W), .USER_EN(1), .USER_W(TX_USER_W), .ID_EN(1), .ID_W(TX_TAG_W)) axis_pkt_2();
+
+taxi_axis_arb_mux #(
+    .S_COUNT(N_UI),
+    .UPDATE_TID(1'b0),
+    .ARB_ROUND_ROBIN(1'b1),
+    .ARB_LSB_HIGH_PRIO(1'b1)
+)
+mux_inst (
+    .clk(clk),
+    .rst(rst),
+
+    /*
+     * AXI4-Stream inputs (sink)
+     */
+    .s_axis(s_axis_pkt_ui),
+
+    /*
+     * AXI4-Stream output (source)
+     */
+    .m_axis(axis_pkt_1)
+);
+
+zircon_ip_len_cksum #(
+    .START_OFFSET(0)
+)
+tx_len_cksum_inst (
+    .clk(clk),
+    .rst(rst),
+
+    /*
+     * Packet passthrough
+     */
+    .s_axis_pkt(axis_pkt_1),
+    .m_axis_pkt(axis_pkt_2),
+
+    /*
+     * Packet metadata output
+     */
+    .m_axis_meta(m_axis_meta_len)
+);
+
+taxi_axis_fifo #(
+    .DEPTH(TX_RAM_SIZE),
+    .RAM_PIPELINE(1),
+    .OUTPUT_FIFO_EN(1'b0),
+    .FRAME_FIFO(1'b0),
+    .USER_BAD_FRAME_VALUE(1'b1),
+    .USER_BAD_FRAME_MASK(1'b1),
+    .DROP_OVERSIZE_FRAME(1'b0),
+    .DROP_BAD_FRAME(1'b0),
+    .DROP_WHEN_FULL(1'b0),
+    .MARK_WHEN_FULL(1'b0),
+    .PAUSE_EN(1'b0)
+)
+tx_fifo_inst (
+    .clk(clk),
+    .rst(rst),
+
+    /*
+     * AXI4-Stream input (sink)
+     */
+    .s_axis(axis_pkt_2),
+
+    /*
+     * AXI4-Stream output (source)
+     */
+    .m_axis(m_axis_pkt),
+
+    /*
+     * Pause
+     */
+    .pause_req(1'b0),
+    .pause_ack(),
+
+    /*
+     * Status
+     */
+    .status_depth(),
+    .status_depth_commit(),
+    .status_overflow(),
+    .status_bad_frame(),
+    .status_good_frame()
+);
+
+endmodule
+
+`resetall