1 /* ir-nec-decoder.c - handle NEC IR Pulse/Space protocol
2  *
3  * Copyright (C) 2010 by Mauro Carvalho Chehab
4  *
5  * This program is free software; you can redistribute it and/or modify
6  *  it under the terms of the GNU General Public License as published by
7  *  the Free Software Foundation version 2 of the License.
8  *
9  *  This program is distributed in the hope that it will be useful,
10  *  but WITHOUT ANY WARRANTY; without even the implied warranty of
11  *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
12  *  GNU General Public License for more details.
13  */
14 
15 #include <linux/bitrev.h>
16 #include <linux/module.h>
17 #include "rc-core-priv.h"
18 
19 #define NEC_NBITS		32
20 #define NEC_UNIT		562500  /* ns */
21 #define NEC_HEADER_PULSE	(16 * NEC_UNIT)
22 #define NECX_HEADER_PULSE	(8  * NEC_UNIT) /* Less common NEC variant */
23 #define NEC_HEADER_SPACE	(8  * NEC_UNIT)
24 #define NEC_REPEAT_SPACE	(4  * NEC_UNIT)
25 #define NEC_BIT_PULSE		(1  * NEC_UNIT)
26 #define NEC_BIT_0_SPACE		(1  * NEC_UNIT)
27 #define NEC_BIT_1_SPACE		(3  * NEC_UNIT)
28 #define	NEC_TRAILER_PULSE	(1  * NEC_UNIT)
29 #define	NEC_TRAILER_SPACE	(10 * NEC_UNIT) /* even longer in reality */
30 #define NECX_REPEAT_BITS	1
31 
32 enum nec_state {
33 	STATE_INACTIVE,
34 	STATE_HEADER_SPACE,
35 	STATE_BIT_PULSE,
36 	STATE_BIT_SPACE,
37 	STATE_TRAILER_PULSE,
38 	STATE_TRAILER_SPACE,
39 };
40 
41 /**
42  * ir_nec_decode() - Decode one NEC pulse or space
43  * @dev:	the struct rc_dev descriptor of the device
44  * @duration:	the struct ir_raw_event descriptor of the pulse/space
45  *
46  * This function returns -EINVAL if the pulse violates the state machine
47  */
48 static int ir_nec_decode(struct rc_dev *dev, struct ir_raw_event ev)
49 {
50 	struct nec_dec *data = &dev->raw->nec;
51 	u32 scancode;
52 	u8 address, not_address, command, not_command;
53 	bool send_32bits = false;
54 
55 	if (!(dev->enabled_protocols & RC_BIT_NEC))
56 		return 0;
57 
58 	if (!is_timing_event(ev)) {
59 		if (ev.reset)
60 			data->state = STATE_INACTIVE;
61 		return 0;
62 	}
63 
64 	IR_dprintk(2, "NEC decode started at state %d (%uus %s)\n",
65 		   data->state, TO_US(ev.duration), TO_STR(ev.pulse));
66 
67 	switch (data->state) {
68 
69 	case STATE_INACTIVE:
70 		if (!ev.pulse)
71 			break;
72 
73 		if (eq_margin(ev.duration, NEC_HEADER_PULSE, NEC_UNIT * 2)) {
74 			data->is_nec_x = false;
75 			data->necx_repeat = false;
76 		} else if (eq_margin(ev.duration, NECX_HEADER_PULSE, NEC_UNIT / 2))
77 			data->is_nec_x = true;
78 		else
79 			break;
80 
81 		data->count = 0;
82 		data->state = STATE_HEADER_SPACE;
83 		return 0;
84 
85 	case STATE_HEADER_SPACE:
86 		if (ev.pulse)
87 			break;
88 
89 		if (eq_margin(ev.duration, NEC_HEADER_SPACE, NEC_UNIT)) {
90 			data->state = STATE_BIT_PULSE;
91 			return 0;
92 		} else if (eq_margin(ev.duration, NEC_REPEAT_SPACE, NEC_UNIT / 2)) {
93 			if (!dev->keypressed) {
94 				IR_dprintk(1, "Discarding last key repeat: event after key up\n");
95 			} else {
96 				rc_repeat(dev);
97 				IR_dprintk(1, "Repeat last key\n");
98 				data->state = STATE_TRAILER_PULSE;
99 			}
100 			return 0;
101 		}
102 
103 		break;
104 
105 	case STATE_BIT_PULSE:
106 		if (!ev.pulse)
107 			break;
108 
109 		if (!eq_margin(ev.duration, NEC_BIT_PULSE, NEC_UNIT / 2))
110 			break;
111 
112 		data->state = STATE_BIT_SPACE;
113 		return 0;
114 
115 	case STATE_BIT_SPACE:
116 		if (ev.pulse)
117 			break;
118 
119 		if (data->necx_repeat && data->count == NECX_REPEAT_BITS &&
120 			geq_margin(ev.duration,
121 			NEC_TRAILER_SPACE, NEC_UNIT / 2)) {
122 				IR_dprintk(1, "Repeat last key\n");
123 				rc_repeat(dev);
124 				data->state = STATE_INACTIVE;
125 				return 0;
126 
127 		} else if (data->count > NECX_REPEAT_BITS)
128 			data->necx_repeat = false;
129 
130 		data->bits <<= 1;
131 		if (eq_margin(ev.duration, NEC_BIT_1_SPACE, NEC_UNIT / 2))
132 			data->bits |= 1;
133 		else if (!eq_margin(ev.duration, NEC_BIT_0_SPACE, NEC_UNIT / 2))
134 			break;
135 		data->count++;
136 
137 		if (data->count == NEC_NBITS)
138 			data->state = STATE_TRAILER_PULSE;
139 		else
140 			data->state = STATE_BIT_PULSE;
141 
142 		return 0;
143 
144 	case STATE_TRAILER_PULSE:
145 		if (!ev.pulse)
146 			break;
147 
148 		if (!eq_margin(ev.duration, NEC_TRAILER_PULSE, NEC_UNIT / 2))
149 			break;
150 
151 		data->state = STATE_TRAILER_SPACE;
152 		return 0;
153 
154 	case STATE_TRAILER_SPACE:
155 		if (ev.pulse)
156 			break;
157 
158 		if (!geq_margin(ev.duration, NEC_TRAILER_SPACE, NEC_UNIT / 2))
159 			break;
160 
161 		address     = bitrev8((data->bits >> 24) & 0xff);
162 		not_address = bitrev8((data->bits >> 16) & 0xff);
163 		command	    = bitrev8((data->bits >>  8) & 0xff);
164 		not_command = bitrev8((data->bits >>  0) & 0xff);
165 
166 		if ((command ^ not_command) != 0xff) {
167 			IR_dprintk(1, "NEC checksum error: received 0x%08x\n",
168 				   data->bits);
169 			send_32bits = true;
170 		}
171 
172 		if (send_32bits) {
173 			/* NEC transport, but modified protocol, used by at
174 			 * least Apple and TiVo remotes */
175 			scancode = data->bits;
176 			IR_dprintk(1, "NEC (modified) scancode 0x%08x\n", scancode);
177 		} else if ((address ^ not_address) != 0xff) {
178 			/* Extended NEC */
179 			scancode = address     << 16 |
180 				   not_address <<  8 |
181 				   command;
182 			IR_dprintk(1, "NEC (Ext) scancode 0x%06x\n", scancode);
183 		} else {
184 			/* Normal NEC */
185 			scancode = address << 8 | command;
186 			IR_dprintk(1, "NEC scancode 0x%04x\n", scancode);
187 		}
188 
189 		if (data->is_nec_x)
190 			data->necx_repeat = true;
191 
192 		rc_keydown(dev, RC_TYPE_NEC, scancode, 0);
193 		data->state = STATE_INACTIVE;
194 		return 0;
195 	}
196 
197 	IR_dprintk(1, "NEC decode failed at count %d state %d (%uus %s)\n",
198 		   data->count, data->state, TO_US(ev.duration), TO_STR(ev.pulse));
199 	data->state = STATE_INACTIVE;
200 	return -EINVAL;
201 }
202 
203 static struct ir_raw_handler nec_handler = {
204 	.protocols	= RC_BIT_NEC,
205 	.decode		= ir_nec_decode,
206 };
207 
208 static int __init ir_nec_decode_init(void)
209 {
210 	ir_raw_handler_register(&nec_handler);
211 
212 	printk(KERN_INFO "IR NEC protocol handler initialized\n");
213 	return 0;
214 }
215 
216 static void __exit ir_nec_decode_exit(void)
217 {
218 	ir_raw_handler_unregister(&nec_handler);
219 }
220 
221 module_init(ir_nec_decode_init);
222 module_exit(ir_nec_decode_exit);
223 
224 MODULE_LICENSE("GPL");
225 MODULE_AUTHOR("Mauro Carvalho Chehab");
226 MODULE_AUTHOR("Red Hat Inc. (http://www.redhat.com)");
227 MODULE_DESCRIPTION("NEC IR protocol decoder");
228