1+ /*
2+ * icebreaker examples - gamma pwm demo
3+ *
4+ * Copyright (C) 2018 Piotr Esden-Tempski <[email protected] > 5+ *
6+ * Permission to use, copy, modify, and/or distribute this software for any
7+ * purpose with or without fee is hereby granted, provided that the above
8+ * copyright notice and this permission notice appear in all copies.
9+ *
10+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
11+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
12+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
13+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
14+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
15+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
16+ * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
17+ *
18+ */
19+
20+ // This example generates PWM with gamma correction
21+ // The intended result is opposite pulsating Red and Green LEDs
22+ // on the iCEBreaker. The intended effect is that the two LED "breathe" evenly
23+ // and don't stay at a perceptable brightness level longer than others.
24+ //
25+ // For more information about gamma correction:
26+ // https://en.wikipedia.org/wiki/Gamma_correction
27+
28+ module top (
29+ input CLK,
30+ output LEDR_N,
31+ output LEDG_N,
32+ output P1A7,
33+ output P1A8,
34+ output P1A9
35+ );
36+
37+ // Gamma value lookup table parameters
38+ parameter G_PW = 8 ; // Number of input bits
39+ parameter G_OW = 16 ; // Number of output bits
40+
41+ // Load the gamma value lookup table
42+ reg [(G_OW- 1 ):0 ] gamma_lut [0 :((1 << (G_PW))- 1 )];
43+ initial $readmemh ("gamma_table.hex" , gamma_lut);
44+
45+ // Very simple dual output PWM generator
46+ // We need two outputs as we can't just invert the gamma corrected PWM output,
47+ // as this would also invert the gamma curve.
48+ reg [15 :0 ] pwm_counter = 0 ;
49+ reg [15 :0 ] pwm_compare_0 = (1 << 15 ) / 2 ;
50+ reg [15 :0 ] pwm_compare_1 = (1 << 15 ) / 2 ;
51+ reg pwm_out_0;
52+ reg pwm_out_1;
53+ always @(posedge CLK) begin
54+ pwm_counter <= pwm_counter + 1 ;
55+
56+ if (pwm_counter < pwm_compare_0) begin
57+ pwm_out_0 <= 1 ;
58+ end else begin
59+ pwm_out_0 <= 0 ;
60+ end
61+
62+ if (pwm_counter < pwm_compare_1) begin
63+ pwm_out_1 <= 1 ;
64+ end else begin
65+ pwm_out_1 <= 0 ;
66+ end
67+ end
68+
69+ // PWM compare value generator
70+ // Fade through the values using the gamma correction
71+ reg [16 :0 ] pwm_inc_counter = 0 ;
72+ reg [G_PW- 1 :0 ] pwm_value = 0 ;
73+ reg pwm_dir = 1 ;
74+ always @(posedge CLK) begin
75+ // Divide clock by 131071
76+ pwm_inc_counter <= pwm_inc_counter + 1 ;
77+
78+ // increment/decrement the index
79+ if (pwm_inc_counter == 0 )
80+ if (pwm_dir)
81+ pwm_value <= pwm_value + 1 ;
82+ else
83+ pwm_value <= pwm_value - 1 ;
84+
85+ // Reverse directions when reaching the index extremes
86+ if (pwm_value == ((1 << G_PW) - 1 ))
87+ pwm_dir <= 0 ;
88+ if (pwm_value == 0 )
89+ pwm_dir <= 1 ;
90+
91+ if (pwm_inc_counter == 1 ) begin
92+ pwm_compare_0 <= gamma_lut[pwm_value];
93+ pwm_compare_1 <= gamma_lut[((1 << G_PW) - 1 ) - pwm_value];
94+ end
95+ end
96+
97+ assign LEDG_N = ~ pwm_out_0;
98+ assign LEDR_N = ~ pwm_out_1;
99+ assign P1A7 = pwm_counter[15 ];
100+ assign P1A8 = pwm_out_0;
101+ assign P1A9 = pwm_out_1;
102+
103+ endmodule
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