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//
// Copyright 2012 Ettus Research LLC
//
// This program 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 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 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/>.
//
// Simple SPI core, the simplest, yet complete spi core I can think of
// Settings register controlled.
// 2 settings regs, control and data
// 1 32-bit readback and status signal
// Settings reg map:
//
// BASE+0 divider setting
// bits [15:0] spi clock divider
//
// BASE+1 configuration input
// bits [23:0] slave select, bit0 = slave0 enabled
// bits [29:24] num bits (1 through 32)
// bit [30] data input edge = in data bit latched on rising edge of clock
// bit [31] data output edge = out data bit latched on rising edge of clock
//
// BASE+2 input data
// Writing this register begins a spi transaction.
// Bits are latched out from bit 0.
// Therefore, load this register in reverse.
//
// Readback
// Bits are latched into bit 0.
// Therefore, data will be in-order.
module simple_spi_core
#(
//settings register base address
parameter BASE = 0,
//width of serial enables (up to 24 is possible)
parameter WIDTH = 8,
//idle state of the spi clock
parameter CLK_IDLE = 0,
//idle state of the serial enables
parameter SEN_IDLE = 24'hffffff
)
(
//clock and synchronous reset
input clock, input reset,
//32-bit settings bus inputs
input set_stb, input [7:0] set_addr, input [31:0] set_data,
//32-bit data readback
output [31:0] readback,
//read is high when spi core can begin another transaction
output ready,
//spi interface, slave selects, clock, data in, data out
output [WIDTH-1:0] sen,
output sclk,
output mosi,
input miso,
//optional debug output
output [31:0] debug
);
wire [15:0] sclk_divider;
setting_reg #(.my_addr(BASE+0),.width(16)) divider_sr(
.clk(clock),.rst(reset),.strobe(set_stb),.addr(set_addr),.in(set_data),
.out(sclk_divider),.changed());
wire [23:0] slave_select;
wire [5:0] num_bits;
wire datain_edge, dataout_edge;
setting_reg #(.my_addr(BASE+1),.width(32)) config_sr(
.clk(clock),.rst(reset),.strobe(set_stb),.addr(set_addr),.in(set_data),
.out({dataout_edge, datain_edge, num_bits, slave_select}),.changed());
wire [31:0] mosi_data;
wire trigger_spi;
setting_reg #(.my_addr(BASE+2),.width(32)) data_sr(
.clk(clock),.rst(reset),.strobe(set_stb),.addr(set_addr),.in(set_data),
.out(mosi_data),.changed(trigger_spi));
localparam WAIT_TRIG = 0;
localparam PRE_IDLE = 1;
localparam CLK_REG = 2;
localparam CLK_INV = 3;
localparam POST_IDLE = 4;
reg [2:0] state;
assign ready = (state == WAIT_TRIG);
//serial clock either idles or is in one of two clock states
reg sclk_reg;
assign sclk = sclk_reg;
//serial enables either idle or enabled based on state
wire [23:0] sen24 = (ready)? SEN_IDLE : (SEN_IDLE ^ slave_select);
reg [WIDTH-1:0] sen_reg;
always @(posedge clock) sen_reg <= sen24[WIDTH-1:0];
assign sen = sen_reg;
//data output shift register
reg [31:0] dataout_reg;
wire [31:0] dataout_next = {dataout_reg[30:0], 1'b0};
assign mosi = dataout_reg[31];
//data input shift register
reg [31:0] datain_reg;
wire [31:0] datain_next = {datain_reg[30:0], miso};
assign readback = datain_reg;
//counter for spi clock
reg [15:0] sclk_counter;
wire sclk_counter_done = (sclk_counter == sclk_divider);
wire [15:0] sclk_counter_next = (sclk_counter_done)? 0 : sclk_counter + 1;
//counter for latching bits miso/mosi
reg [6:0] bit_counter;
wire [6:0] bit_counter_next = bit_counter + 1;
wire bit_counter_done = (bit_counter_next == num_bits);
always @(posedge clock) begin
if (reset) begin
state <= WAIT_TRIG;
sclk_reg <= CLK_IDLE;
end
else begin
case (state)
WAIT_TRIG: begin
if (trigger_spi) state <= PRE_IDLE;
sclk_counter <= 0;
sclk_reg <= CLK_IDLE;
end
PRE_IDLE: begin
if (sclk_counter_done) state <= CLK_REG;
sclk_counter <= sclk_counter_next;
dataout_reg <= mosi_data;
bit_counter <= 0;
sclk_reg <= CLK_IDLE;
end
CLK_REG: begin
if (sclk_counter_done) begin
state <= CLK_INV;
if (datain_edge != CLK_IDLE) datain_reg <= datain_next;
if (dataout_edge != CLK_IDLE) dataout_reg <= dataout_next;
sclk_reg <= ~CLK_IDLE;
end
sclk_counter <= sclk_counter_next;
end
CLK_INV: begin
if (sclk_counter_done) begin
state <= (bit_counter_done)? POST_IDLE : CLK_REG;
bit_counter <= bit_counter_next;
if (datain_edge == CLK_IDLE) datain_reg <= datain_next;
if (dataout_edge == CLK_IDLE) dataout_reg <= dataout_next;
sclk_reg <= CLK_IDLE;
end
sclk_counter <= sclk_counter_next;
end
POST_IDLE: begin
if (sclk_counter_done) state <= WAIT_TRIG;
sclk_counter <= sclk_counter_next;
sclk_reg <= CLK_IDLE;
end
default: state <= WAIT_TRIG;
endcase //state
end
end
assign debug = {
trigger_spi, state, //4
sclk, mosi, miso, ready, //4
sen[7:0], //8
1'b0, bit_counter[6:0], //8
sclk_counter_done, bit_counter_done, //2
sclk_counter[5:0] //6
};
endmodule //simple_spi_core
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