jtag_vpi.v

/*
 * TCP/IP controlled VPI JTAG Interface.
 * Based on Julius Baxter's work on jp_vpi.c
 *
 * SPDX-FileCopyrightText: 2012 Franck Jullien <franck.jullien@gmail.com>
 * SPDX-License-Identifier: BSD-3-Clause
 */

`define CMD_RESET		0
`define CMD_TMS_SEQ		1
`define CMD_SCAN_CHAIN		2
`define CMD_SCAN_CHAIN_FLIP_TMS	3
`define CMD_STOP_SIMU		4

module jtag_vpi
#(	parameter DEBUG_INFO = 0,
	parameter TP = 1,
	parameter TCK_HALF_PERIOD = 50, // Clock half period (Clock period = 100 ns => 10 MHz)
	parameter  CMD_DELAY = 1000
)
(
	output reg	tms,
	output reg	tck,
	output reg	tdi,
	input		tdo,
	input		enable,
	input		init_done);

integer		cmd;
integer		length;
integer		nb_bits;

reg [31:0]	buffer_out [0:4095];   // Data storage from the jtag server
reg [31:0]	buffer_in  [0:4095];   // Data storage to the jtag server

integer		flip_tms;

reg [31:0]	data_out;
reg [31:0]	data_in;

integer		debug;

assign		tms_o = tms;
assign		tck_o = tck;
assign		tdi_o = tdi;

initial
begin
	tck		<= #TP 1'b0;
	tdi		<= #TP 1'bz;
	tms		<= #TP 1'b0;

	data_out	<= 32'h0;
	data_in		<= 32'h0;

	// Insert a #delay here because we need to
	// wait until the PC isn't pointing to flash anymore
	// (this is around 20k ns if the flash_crash boot code
	// is being booted from, else much bigger, around 10mil ns)
	wait(init_done)
		if($test$plusargs("jtag_vpi_enable")) main;
end

task main;
begin
	$display("JTAG debug module with VPI interface enabled\n");

	reset_tap;
	goto_run_test_idle_from_reset;

	while (1) begin

		// Check for incoming command
		// wait until a command is sent
		// poll with a delay here
		cmd = -1;

		while (cmd == -1)
		begin
			#CMD_DELAY $check_for_command(cmd, length, nb_bits, buffer_out);
		end

		// now switch on the command
		case (cmd)

		`CMD_RESET :
		begin
			if (DEBUG_INFO)
				$display("%t ----> CMD_RESET %h\n", $time, length);
			reset_tap;
			goto_run_test_idle_from_reset;
		end

		`CMD_TMS_SEQ :
		begin
			if (DEBUG_INFO)
				$display("%t ----> CMD_TMS_SEQ\n", $time);
			do_tms_seq;
		end

		`CMD_SCAN_CHAIN :
		begin
			if (DEBUG_INFO)
				$display("%t ----> CMD_SCAN_CHAIN\n", $time);
			flip_tms = 0;
			do_scan_chain;
			$send_result_to_server(length, buffer_in);
		end

		`CMD_SCAN_CHAIN_FLIP_TMS :
		begin
			if(DEBUG_INFO)
				$display("%t ----> CMD_SCAN_CHAIN\n", $time);
			flip_tms = 1;
			do_scan_chain;
			$send_result_to_server(length, buffer_in);
		end

		`CMD_STOP_SIMU :
		begin
			if(DEBUG_INFO)
				$display("%t ----> End of simulation\n", $time);
			$finish();
		end

		default:
		begin
			$display("Somehow got to the default case in the command case statement.");
			$display("Command was: %x", cmd);
			$display("Exiting...");
			$finish();
		end

		endcase // case (cmd)

	end // while (1)
end

endtask // main


// Generation of the TCK signal
task gen_clk;
input [31:0] number;
integer i;

begin
	for (i = 0; i < number; i = i + 1)
	begin
		#TCK_HALF_PERIOD tck <= 1;
		#TCK_HALF_PERIOD tck <= 0;
	end
end

endtask

// TAP reset
task reset_tap;
begin
	if (DEBUG_INFO)
		$display("(%0t) Task reset_tap", $time);
	tms <= #1 1'b1;
	gen_clk(5);
end

endtask


// Goes to RunTestIdle state
task goto_run_test_idle_from_reset;
begin
	if (DEBUG_INFO)
		$display("(%0t) Task goto_run_test_idle_from_reset", $time);
	tms <= #1 1'b0;
	gen_clk(1);
end

endtask

//
task do_tms_seq;

integer		i,j;
reg [31:0]	data;
integer		nb_bits_rem;
integer		nb_bits_in_this_byte;

begin
	if (DEBUG_INFO)
		$display("(%0t) Task do_tms_seq of %d bits (length = %d)", $time, nb_bits, length);

	// Number of bits to send in the last byte
	nb_bits_rem = nb_bits % 8;

	for (i = 0; i < length; i = i + 1)
	begin
		// If we are in the last byte, we have to send only
		// nb_bits_rem bits. If not, we send the whole byte.
		nb_bits_in_this_byte = (i == (length - 1)) ? nb_bits_rem : 8;

		data = buffer_out[i];
		for (j = 0; j < nb_bits_in_this_byte; j = j + 1)
		begin
			tms <= #1 1'b0;
			if (data[j] == 1) begin
				tms <= #1 1'b1;
			end
			gen_clk(1);
		end
	end

	tms <= #1 1'b0;
end

endtask


//
task do_scan_chain;

integer		_bit;
integer		nb_bits_rem;
integer		nb_bits_in_this_byte;
integer		index;

begin
	if(DEBUG_INFO)
		$display("(%0t) Task do_scan_chain of %d bits (length = %d)", $time, nb_bits, length);

	// Number of bits to send in the last byte
	nb_bits_rem = nb_bits % 8;

	for (index = 0; index < length; index = index + 1)
	begin
		// If we are in the last byte, we have to send only
		// nb_bits_rem bits if it's not zero.
		// If not, we send the whole byte.
		nb_bits_in_this_byte = (index == (length - 1)) ? ((nb_bits_rem == 0) ? 8 : nb_bits_rem) : 8;

		data_out = buffer_out[index];
		for (_bit = 0; _bit < nb_bits_in_this_byte; _bit = _bit + 1)
		begin
			tdi <= 1'b0;
			if (data_out[_bit] == 1'b1) begin
				tdi <= 1'b1;
			end

			// On the last bit, set TMS to '1'
			if (((_bit == (nb_bits_in_this_byte - 1)) && (index == (length - 1))) && (flip_tms == 1)) begin
				tms <= 1'b1;
			end

			#TCK_HALF_PERIOD tck <= 1;
			data_in[_bit] <= tdo;
			#TCK_HALF_PERIOD tck <= 0;
		end
		buffer_in[index] = data_in;
	end

	tdi <= 1'b0;
	tms <= 1'b0;
end

endtask

endmodule