data_io.v

//
// data_io.v
//
// data_io for the MiST board
// http://code.google.com/p/mist-board/
//
// Copyright (c) 2014 Till Harbaum <till@harbaum.org>
// Copyright (c) 2015-2017 Sorgelig
// Copyright (c) 2019 György Szombathelyi
//
// This source file is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published
// by the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// This source file 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 General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with this program.  If not, see <http://www.gnu.org/licenses/>.
//
///////////////////////////////////////////////////////////////////////

module data_io
(
	// Global clock. It should be around 100MHz (higher is better).
	input             clk_sys,

	// Global SPI clock from ARM. 24MHz
	input             SPI_SCK,
	input             SPI_SS2,
	input             SPI_DI,

	// ARM -> FPGA download
	input             ioctl_clkref,
	output reg        ioctl_download = 0, // signal indicating an active download
	output reg  [7:0] ioctl_index,        // menu index used to upload the file
	output reg        ioctl_wr = 0,
	output reg [24:0] ioctl_addr,
	output reg [15:0] ioctl_dout
);

///////////////////////////////   DOWNLOADING   ///////////////////////////////

localparam UIO_FILE_TX      = 8'h53;
localparam UIO_FILE_TX_DAT  = 8'h54;
localparam UIO_FILE_INDEX   = 8'h55;
// SPI receiver IO -> FPGA

reg       spi_receiver_strobe_r = 0;
reg       spi_transfer_end_r = 1;
reg [7:0] spi_byte_in;

// data_io has its own SPI interface to the io controller
// Read at spi_sck clock domain, assemble bytes for transferring to clk_sys
always@(posedge SPI_SCK or posedge SPI_SS2) begin

	reg  [6:0] sbuf;
	reg  [2:0] bit_cnt;

	if(SPI_SS2) begin
		spi_transfer_end_r <= 1;
		bit_cnt <= 0;
	end else begin
		spi_transfer_end_r <= 0;
		
		bit_cnt <= bit_cnt + 1'd1;

		if(bit_cnt != 7)
			sbuf[6:0] <= { sbuf[5:0], SPI_DI };

		// finished reading a byte, prepare to transfer to clk_sys
        if(bit_cnt == 7) begin
			spi_byte_in <= { sbuf, SPI_DI};
			spi_receiver_strobe_r <= ~spi_receiver_strobe_r;
		end
	end
end

always @(posedge clk_sys) begin

	reg        spi_receiver_strobe;
	reg        spi_transfer_end;
	reg        spi_receiver_strobeD;
	reg        spi_transfer_endD;
	reg  [7:0] acmd;
	reg  [2:0] abyte_cnt;   // counts bytes
	reg [24:0] addr;
	reg        wr_int;
	reg        clkrefD;
	reg        hi;

	//synchronize between SPI and sys clock domains
	spi_receiver_strobeD <= spi_receiver_strobe_r;
	spi_receiver_strobe <= spi_receiver_strobeD;
	spi_transfer_endD <= spi_transfer_end_r;
	spi_transfer_end <= spi_transfer_endD;

	if (~spi_transfer_endD & spi_transfer_end) begin
		abyte_cnt <= 3'd0;
	end else if (spi_receiver_strobeD ^ spi_receiver_strobe) begin
		if(~&abyte_cnt) abyte_cnt <= abyte_cnt + 1'd1;

		if(abyte_cnt == 0) begin
			acmd <= spi_byte_in;
			hi <= 0;
		end else begin
			case (acmd)
				UIO_FILE_TX: begin
				// prepare 
					if(spi_byte_in) begin
						addr <= 0;
						ioctl_download <= 1; 
					end else begin
						ioctl_addr <= addr;
						ioctl_download <= 0;
					end
				end

				// transfer
				UIO_FILE_TX_DAT: begin
					ioctl_addr <= addr;
					if (hi) ioctl_dout[7:0] <= spi_byte_in; else ioctl_dout[15:8] <= spi_byte_in;
					hi <= ~hi;
					if (hi) wr_int <= 1;
				end

				// expose file (menu) index
				UIO_FILE_INDEX: ioctl_index <= spi_byte_in;
			endcase
		end
	end

	ioctl_wr <= 0;
	clkrefD <= ioctl_clkref;
	if (wr_int & ~clkrefD & ioctl_clkref) begin
		addr <= addr + 1'd1;
		ioctl_wr <= 1;
		wr_int <= 0;
	end
end

endmodule