1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
|
//
// Copyright 2011 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/>.
//
////////////////////////////////////////////////////////////////////////
// GPMC to FIFO
//
// Reads frames from BRAM pages and writes them into FIFO interface.
// The GPMC is asynchronously alerted when a BRAM page is available.
//
// EM_CLK:
// A GPMC read transaction consists of one EM_CLK cycle (idle low).
//
// EM_WE:
// Write enable is actually the combination of ~NWE & ~NCS.
// The write enable is active for the entire transaction.
//
// EM_D:
// Data is set on the rising edge and written into BRAM on the falling edge.
//
// EM_A:
// Address is set on the rising edge and read by BRAM on the falling edge.
////////////////////////////////////////////////////////////////////////
module gpmc_to_fifo
#(parameter PTR_WIDTH = 2, parameter ADDR_WIDTH = 10)
(input [15:0] EM_D, input [ADDR_WIDTH:1] EM_A, input EM_CLK, input EM_WE,
input clk, input reset, input clear, input arst,
output [17:0] data_o, output src_rdy_o, input dst_rdy_i,
output reg have_space);
//states for the GPMC side of things
wire [17:0] data_i;
reg gpmc_state;
reg [ADDR_WIDTH:1] last_addr;
reg [PTR_WIDTH:0] gpmc_ptr, next_gpmc_ptr;
localparam GPMC_STATE_START = 0;
localparam GPMC_STATE_FILL = 1;
//states for the FIFO side of things
reg fifo_state;
reg [ADDR_WIDTH-1:0] counter;
reg [PTR_WIDTH:0] fifo_ptr;
localparam FIFO_STATE_CLAIM = 0;
localparam FIFO_STATE_EMPTY = 1;
//------------------------------------------------------------------
// State machine to control the data from GPMC to BRAM
//------------------------------------------------------------------
always @(negedge EM_CLK or posedge arst) begin
if (arst) begin
gpmc_state <= GPMC_STATE_START;
gpmc_ptr <= 0;
next_gpmc_ptr <= 0;
end
else if (EM_WE) begin
case(gpmc_state)
GPMC_STATE_START: begin
if (EM_A == 2) begin
gpmc_state <= GPMC_STATE_FILL;
last_addr <= {EM_D[ADDR_WIDTH-2:0], 1'b0} - 1'b1 + 2;
next_gpmc_ptr <= gpmc_ptr + 1;
end
end
GPMC_STATE_FILL: begin
if (data_i[17]) begin
gpmc_state <= GPMC_STATE_START;
gpmc_ptr <= next_gpmc_ptr;
end
end
endcase //gpmc_state
end //EM_WE
end //always
//------------------------------------------------------------------
// A block ram is available to empty when the pointers dont match.
//------------------------------------------------------------------
wire [PTR_WIDTH:0] safe_gpmc_ptr;
cross_clock_reader #(.WIDTH(PTR_WIDTH+1)) read_gpmc_ptr
(.clk(clk), .rst(reset | clear), .in(gpmc_ptr), .out(safe_gpmc_ptr));
wire bram_available_to_empty = safe_gpmc_ptr != fifo_ptr;
//------------------------------------------------------------------
// Glich free generation of have space signal:
// High when the fifo pointer has not caught up to the gpmc pointer.
//------------------------------------------------------------------
wire [PTR_WIDTH:0] safe_next_gpmc_ptr;
cross_clock_reader #(.WIDTH(PTR_WIDTH+1)) read_next_gpmc_ptr
(.clk(clk), .rst(reset | clear), .in(next_gpmc_ptr), .out(safe_next_gpmc_ptr));
always @(posedge clk)
if (reset | clear) have_space <= 0;
else have_space <= (fifo_ptr ^ (1 << PTR_WIDTH)) != safe_next_gpmc_ptr;
//------------------------------------------------------------------
// State machine to control the data from BRAM to FIFO
//------------------------------------------------------------------
always @(posedge clk) begin
if (reset | clear) begin
fifo_state <= FIFO_STATE_CLAIM;
fifo_ptr <= 0;
counter <= 2;
end
else begin
case(fifo_state)
FIFO_STATE_CLAIM: begin
if (bram_available_to_empty) fifo_state <= FIFO_STATE_EMPTY;
counter <= 2;
end
FIFO_STATE_EMPTY: begin
if (src_rdy_o && dst_rdy_i && data_o[17]) begin
fifo_state <= FIFO_STATE_CLAIM;
fifo_ptr <= fifo_ptr + 1;
end
if (src_rdy_o && dst_rdy_i) begin
counter <= counter + 1;
end
end
endcase //fifo_state
end
end //always
assign src_rdy_o = fifo_state == FIFO_STATE_EMPTY;
//assign data and frame bits to bram input
assign data_i[15:0] = EM_D;
assign data_i[16] = (gpmc_state == GPMC_STATE_START);
assign data_i[17] = (EM_A == last_addr);
//instantiate dual ported bram for async read + write
ram_2port #(.DWIDTH(18),.AWIDTH(PTR_WIDTH + ADDR_WIDTH)) async_fifo_bram
(.clka(~EM_CLK),.ena(1'b1),.wea(EM_WE),
.addra({gpmc_ptr[PTR_WIDTH-1:0], EM_A}),.dia(data_i),.doa(),
.clkb(~clk),.enb(1'b1),.web(1'b0),
.addrb({fifo_ptr[PTR_WIDTH-1:0], counter}),.dib(18'h3ffff),.dob(data_o));
endmodule // gpmc_to_fifo
|
