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repo2/mist/user_io.v @ 446

//
// user_io.v
//
// user_io for the MiST board
// http://code.google.com/p/mist-board/
//
// Copyright (c) 2014 Till Harbaum <till@harbaum.org>
//
// This source file is free software: you can redistribute it and/or modify
// it under the terms of the Lesser 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/>.
//

// parameter STRLEN and the actual length of conf_str have to match
module user_io #(parameter STRLEN=0) (
input [(8*STRLEN)-1:0] conf_str,

input SPI_CLK,
input SPI_SS_IO,
output reg SPI_MISO,
input SPI_MOSI,
output reg [5:0] joystick_0,
output reg [5:0] joystick_1,
output reg [15:0] joystick_analog_0,
output reg [15:0] joystick_analog_1,
output [1:0] buttons,
output [1:0] switches,

output reg [7:0] status,

// connection to sd card emulation
input [31:0] sd_lba,
input sd_rd,
input sd_wr,
output reg sd_ack,
input sd_conf,
input sd_sdhc,
output reg [7:0] sd_dout,
output reg sd_dout_strobe,
input [7:0] sd_din,
output reg sd_din_strobe,

// ps2 keyboard emulation
input ps2_clk, // 12-16khz provided by core
output ps2_kbd_clk,
output reg ps2_kbd_data,

// serial com port
input [7:0] serial_data,
input serial_strobe
);

reg [6:0] sbuf;
reg [7:0] cmd;
reg [2:0] bit_cnt; // counts bits 0-7 0-7 ...
reg [7:0] byte_cnt; // counts bytes
reg [5:0] joystick0;
reg [5:0] joystick1;
reg [3:0] but_sw;
reg [2:0] stick_idx;

assign buttons = but_sw[1:0];
assign switches = but_sw[3:2];

// this variant of user_io is for 8 bit cores (type == a4) only
wire [7:0] core_type = 8'ha4;

// command byte read by the io controller
wire [7:0] sd_cmd = { 4'h5, sd_conf, sd_sdhc, sd_wr, sd_rd };

// filter spi clock. the 8 bit gate delay is ~2.5ns in total
wire [7:0] spi_sck_D = { spi_sck_D[6:0], SPI_CLK } /* synthesis keep */;
wire spi_sck = (spi_sck && spi_sck_D != 8'h00) || (!spi_sck && spi_sck_D == 8'hff);

// drive MISO only when transmitting core id
always@(negedge spi_sck or posedge SPI_SS_IO) begin
if(SPI_SS_IO == 1) begin
SPI_MISO <= 1'bZ;
end else begin

// first byte returned is always core type, further bytes are
// command dependent
if(byte_cnt == 0) begin
SPI_MISO <= core_type[~bit_cnt];

end else begin
// reading serial fifo
if(cmd == 8'h1b) begin
// send alternating flag byte and data
if(byte_cnt[0]) SPI_MISO <= serial_out_status[~bit_cnt];
else SPI_MISO <= serial_out_byte[~bit_cnt];
end
// reading config string
else if(cmd == 8'h14) begin
// returning a byte from string
if(byte_cnt < STRLEN + 1)
SPI_MISO <= conf_str[{STRLEN - byte_cnt,~bit_cnt}];
else
SPI_MISO <= 1'b0;
end
// reading sd card status
else if(cmd == 8'h16) begin
if(byte_cnt == 1)
SPI_MISO <= sd_cmd[~bit_cnt];
else if((byte_cnt >= 2) && (byte_cnt < 6))
SPI_MISO <= sd_lba[{5-byte_cnt, ~bit_cnt}];
else
SPI_MISO <= 1'b0;
end
// reading sd card write data
else if(cmd == 8'h18)
SPI_MISO <= sd_din[~bit_cnt];
else
SPI_MISO <= 1'b0;
end
end
end

// 8 byte fifo to store ps2 bytes
localparam PS2_FIFO_BITS = 3;
reg [7:0] ps2_fifo [(2**PS2_FIFO_BITS)-1:0];
reg [PS2_FIFO_BITS-1:0] ps2_wptr;
reg [PS2_FIFO_BITS-1:0] ps2_rptr;

// ps2 transmitter state machine
reg [3:0] ps2_tx_state;
reg [7:0] ps2_tx_byte;
reg ps2_parity;

assign ps2_kbd_clk = ps2_clk || (ps2_tx_state == 0);

// ps2 transmitter
// Takes a byte from the FIFO and sends it in a ps2 compliant serial format.
reg ps2_r_inc;
always@(posedge ps2_clk) begin
ps2_r_inc <= 1'b0;
if(ps2_r_inc)
ps2_rptr <= ps2_rptr + 1;

// transmitter is idle?
if(ps2_tx_state == 0) begin
// data in fifo present?
if(ps2_wptr != ps2_rptr) begin
// load tx register from fifo
ps2_tx_byte <= ps2_fifo[ps2_rptr];
ps2_r_inc <= 1'b1;
// reset parity
ps2_parity <= 1'b1;
// start transmitter
ps2_tx_state <= 4'd1;

// put start bit on data line
ps2_kbd_data <= 1'b0; // start bit is 0
end
end else begin
// transmission of 8 data bits
if((ps2_tx_state >= 1)&&(ps2_tx_state < 9)) begin
ps2_kbd_data <= ps2_tx_byte[0]; // data bits
ps2_tx_byte[6:0] <= ps2_tx_byte[7:1]; // shift down
if(ps2_tx_byte[0])
ps2_parity <= !ps2_parity;
end

// transmission of parity
if(ps2_tx_state == 9)
ps2_kbd_data <= ps2_parity;
// transmission of stop bit
if(ps2_tx_state == 10)
ps2_kbd_data <= 1'b1; // stop bit is 1

// advance state machine
if(ps2_tx_state < 11)
ps2_tx_state <= ps2_tx_state + 4'd1;
else
ps2_tx_state <= 4'd0;
end
end
// fifo to receive serial data from core to be forwarded to io controller

// 16 byte fifo to store serial bytes
localparam SERIAL_OUT_FIFO_BITS = 6;
reg [7:0] serial_out_fifo [(2**SERIAL_OUT_FIFO_BITS)-1:0];
reg [SERIAL_OUT_FIFO_BITS-1:0] serial_out_wptr;
reg [SERIAL_OUT_FIFO_BITS-1:0] serial_out_rptr;
wire serial_out_data_available = serial_out_wptr != serial_out_rptr;
wire [7:0] serial_out_byte = serial_out_fifo[serial_out_rptr] /* synthesis keep */;
wire [7:0] serial_out_status = { 7'b1000000, serial_out_data_available};

// status[0] is reset signal from io controller and is thus used to flush
// the fifo
always @(posedge serial_strobe or posedge status[0]) begin
if(status[0] == 1) begin
serial_out_wptr <= 0;
end else begin
serial_out_fifo[serial_out_wptr] <= serial_data;
serial_out_wptr <= serial_out_wptr + 1;
end
end

always@(negedge spi_sck or posedge status[0]) begin
if(status[0] == 1) begin
serial_out_rptr <= 0;
end else begin
if((byte_cnt != 0) && (cmd == 8'h1b)) begin
// read last bit -> advance read pointer
if((bit_cnt == 7) && !byte_cnt[0] && serial_out_data_available)
serial_out_rptr <= serial_out_rptr + 1;
end
end
end

// SPI receiver
always@(posedge spi_sck or posedge SPI_SS_IO) begin

if(SPI_SS_IO == 1) begin
bit_cnt <= 3'd0;
byte_cnt <= 8'd0;
sd_ack <= 1'b0;
sd_dout_strobe <= 1'b0;
sd_din_strobe <= 1'b0;
end else begin
sd_dout_strobe <= 1'b0;
sd_din_strobe <= 1'b0;
sbuf[6:0] <= { sbuf[5:0], SPI_MOSI };
bit_cnt <= bit_cnt + 3'd1;
if((bit_cnt == 7)&&(byte_cnt != 8'd255))
byte_cnt <= byte_cnt + 8'd1;

// finished reading command byte
if(bit_cnt == 7) begin
if(byte_cnt == 0) begin
cmd <= { sbuf, SPI_MOSI};
// fetch first byte when sectore FPGA->IO command has been seen
if({ sbuf, SPI_MOSI} == 8'h18)
sd_din_strobe <= 1'b1;
if(({ sbuf, SPI_MOSI} == 8'h17) || ({ sbuf, SPI_MOSI} == 8'h18))
sd_ack <= 1'b1;
end else begin
// buttons and switches
if(cmd == 8'h01)
but_sw <= { sbuf[2:0], SPI_MOSI };

if(cmd == 8'h02)
joystick_0 <= { sbuf[4:0], SPI_MOSI };
if(cmd == 8'h03)
joystick_1 <= { sbuf[4:0], SPI_MOSI };
if(cmd == 8'h05) begin
// store incoming keyboard bytes in
ps2_fifo[ps2_wptr] <= { sbuf, SPI_MOSI };
ps2_wptr <= ps2_wptr + 1;
end
if(cmd == 8'h15)
status <= { sbuf[6:0], SPI_MOSI };
// send sector IO -> FPGA
if(cmd == 8'h17) begin
// flag that download begins
sd_dout <= { sbuf, SPI_MOSI};
sd_dout_strobe <= 1'b1;
end
// send sector FPGA -> IO
if(cmd == 8'h18)
sd_din_strobe <= 1'b1;
// send SD config IO -> FPGA
if(cmd == 8'h19) begin
// flag that download begins
sd_dout <= { sbuf, SPI_MOSI};
// sd card knows data is config if sd_dout_strobe is asserted
// with sd_ack still being inactive (low)
sd_dout_strobe <= 1'b1;
end
// joystick analog
if(cmd == 8'h1a) begin
// first byte is joystick indes
if(byte_cnt == 1)
stick_idx <= { sbuf[1:0], SPI_MOSI };
else if(byte_cnt == 2) begin
// second byte is x axis
if(stick_idx == 0)
joystick_analog_0[15:8] <= { sbuf, SPI_MOSI };
else if(stick_idx == 1)
joystick_analog_1[15:8] <= { sbuf, SPI_MOSI };
end else if(byte_cnt == 3) begin
// third byte is y axis
if(stick_idx == 0)
joystick_analog_0[7:0] <= { sbuf, SPI_MOSI };
else if(stick_idx == 1)
joystick_analog_1[7:0] <= { sbuf, SPI_MOSI };
end
end

end
end
end
end
endmodule
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