doom_riscv/cores/e1/rtl/e1_tx.v

/*
 * e1_tx.v
 *
 * vim: ts=4 sw=4
 *
 * E1 TX top-level
 *
 *
 * Copyright (C) 2019  Sylvain Munaut <tnt@246tNt.com>
 * All rights reserved.
 *
 * LGPL v3+, see LICENSE.lgpl3
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 3 of the License, or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public License
 * along with this program; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
 */

`default_nettype none

module e1_tx #(
	parameter integer MFW = 7
)(
	// IO pads
	output wire pad_tx_hi,
	output wire pad_tx_lo,

	// Buffer interface
	input  wire [7:0] buf_data,
	output wire [4:0] buf_ts,
	output wire [3:0] buf_frame,
	output wire [MFW-1:0] buf_mf,
	output wire buf_re,
	input  wire buf_rdy,

	// BD interface
	input  wire [MFW-1:0] bd_mf,
	input  wire [1:0] bd_crc_e,
	input  wire bd_valid,
	output reg  bd_done,
	output reg  bd_miss,

	// Loopback input
	input  wire lb_bit,
	input  wire lb_valid,

	// Control
	input  wire ctrl_time_src,  // 0=internal, 1=external
	input  wire ctrl_do_framing,
	input  wire ctrl_do_crc4,
	input  wire ctrl_loopback,
	input  wire alarm,

	// Timing sources
	input  wire ext_tick,
	output wire int_tick,

	// Common
	input  wire clk,
	input  wire rst
);

	// Signals
	// -------

	// Buffer Descriptor handling
	reg  mf_valid;

	// Framer
	wire [7:0] f_data;
	wire [1:0] f_crc_e;
	wire [3:0] f_frame;
	wire [4:0] f_ts;
	wire f_mf_first;
	wire f_mf_last;
	wire f_req;
	wire f_rdy;

	// Low-level (bit -> pulses)
	wire ll_bit, ll_valid;
	wire ll_pg_hi,  ll_pg_lo, ll_pg_stb;
	wire ll_raw_hi, ll_raw_lo;

	// Pulse generator
	reg  [4:0] pg_hi;
	reg  [4:0] pg_lo;


	// Frame generation
	// ----------------

	// Buffer Descriptor
		// Keep track if we're in a valid MF at all
	always @(posedge clk or posedge rst)
		if (rst)
			mf_valid <= 1'b0;
		else if (f_req & f_mf_first)
			mf_valid <= bd_valid;

		// We register those because a 1 cycle delay doesn't matter
	always @(posedge clk)
	begin
		bd_done <= f_req & f_mf_last  &  mf_valid;
		bd_miss <= f_req & f_mf_first & ~bd_valid;
	end

	// Buffer read
	assign buf_ts    = f_ts;
	assign buf_frame = f_frame;
	assign buf_mf    = bd_mf;
	assign buf_re    = f_req & bd_valid;

	assign f_data  = buf_data;
	assign f_crc_e = bd_crc_e;
	assign f_rdy   = buf_rdy & mf_valid;

	// Framer
	e1_tx_framer framer_I (
		.in_data(f_data),
		.in_crc_e(f_crc_e),
		.in_frame(f_frame),
		.in_ts(f_ts),
		.in_mf_first(f_mf_first),
		.in_mf_last(f_mf_last),
		.in_req(f_req),
		.in_rdy(f_rdy),
		.out_bit(ll_bit),
		.out_valid(ll_valid),
		.lb_bit(lb_bit),
		.lb_valid(lb_valid),
		.ctrl_time_src(ctrl_time_src),
		.ctrl_do_framing(ctrl_do_framing),
		.ctrl_do_crc4(ctrl_do_crc4),
		.ctrl_loopback(ctrl_loopback),
		.alarm(alarm),
		.ext_tick(ext_tick),
		.int_tick(int_tick),
		.clk(clk),
		.rst(rst)
	);


	// Low-level
	// ---------

	// HDB3 encoding
	hdb3_enc hdb3_I (
		.out_pos(ll_pg_hi),
		.out_neg(ll_pg_lo),
		.out_valid(ll_pg_stb),
		.in_data(ll_bit),
		.in_valid(ll_valid),
		.clk(clk),
		.rst(rst)
	);

	// Pulse generation
	always @(posedge clk)
	begin
		if (rst) begin
			pg_hi <= 0;
			pg_lo <= 0;
		end else begin
			if (ll_pg_stb) begin
				pg_hi <= ll_pg_hi ? 5'h19 : 5'h00;
				pg_lo <= ll_pg_lo ? 5'h19 : 5'h00;
			end else begin
				pg_hi <= pg_hi - pg_hi[4];
				pg_lo <= pg_lo - pg_lo[4];
			end
		end
	end

	assign ll_raw_hi = pg_hi[4];
	assign ll_raw_lo = pg_lo[4];

	// PHY
	e1_tx_phy phy_I (
		.pad_tx_hi(pad_tx_hi),
		.pad_tx_lo(pad_tx_lo),
		.tx_hi(ll_raw_hi),
		.tx_lo(ll_raw_lo),
		.clk(clk),
		.rst(rst)
	);

endmodule // e1_tx