text: /* ir-nec-decoder.c - handle NEC IR Pulse/Space protocol
   *
   * Copyright (C) 2010 by Mauro Carvalho Chehab <mchehab@redhat.com>
   *
   * 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 version 2 of the License.
   *
   *  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.
   */
  
  #include <linux/bitrev.h>
  #include <linux/module.h>
  #include "rc-core-priv.h"
  
  #define NEC_NBITS		32
  #define NEC_UNIT		562500  /* ns */
  #define NEC_HEADER_PULSE	(16 * NEC_UNIT)
  #define NECX_HEADER_PULSE	(8  * NEC_UNIT) /* Less common NEC variant */
  #define NEC_HEADER_SPACE	(8  * NEC_UNIT)
  #define NEC_REPEAT_SPACE	(4  * NEC_UNIT)
  #define NEC_BIT_PULSE		(1  * NEC_UNIT)
  #define NEC_BIT_0_SPACE		(1  * NEC_UNIT)
  #define NEC_BIT_1_SPACE		(3  * NEC_UNIT)
  #define	NEC_TRAILER_PULSE	(1  * NEC_UNIT)
  #define	NEC_TRAILER_SPACE	(10 * NEC_UNIT) /* even longer in reality */
  #define NECX_REPEAT_BITS	1
  
  enum nec_state {
  	STATE_INACTIVE,
  	STATE_HEADER_SPACE,
  	STATE_BIT_PULSE,
  	STATE_BIT_SPACE,
  	STATE_TRAILER_PULSE,
  	STATE_TRAILER_SPACE,
  };
  
  /**
   * ir_nec_decode() - Decode one NEC pulse or space
   * @dev:	the struct rc_dev descriptor of the device
   * @duration:	the struct ir_raw_event descriptor of the pulse/space
   *
   * This function returns -EINVAL if the pulse violates the state machine
   */
  static int ir_nec_decode(struct rc_dev *dev, struct ir_raw_event ev)
  {
  	struct nec_dec *data = &dev->raw->nec;
  	u32 scancode;
  	u8 address, not_address, command, not_command;
  	bool send_32bits = false;
  
  	if (!(dev->enabled_protocols & RC_BIT_NEC))
  		return 0;
  
  	if (!is_timing_event(ev)) {
  		if (ev.reset)
  			data->state = STATE_INACTIVE;
  		return 0;
  	}
  
  	IR_dprintk(2, "NEC decode started at state %d (%uus %s)\n",
  		   data->state, TO_US(ev.duration), TO_STR(ev.pulse));
  
  	switch (data->state) {
  
  	case STATE_INACTIVE:
  		if (!ev.pulse)
  			break;
  
  		if (eq_margin(ev.duration, NEC_HEADER_PULSE, NEC_UNIT * 2)) {
  			data->is_nec_x = false;
  			data->necx_repeat = false;
  		} else if (eq_margin(ev.duration, NECX_HEADER_PULSE, NEC_UNIT / 2))
  			data->is_nec_x = true;
  		else
  			break;
  
  		data->count = 0;
  		data->state = STATE_HEADER_SPACE;
  		return 0;
  
  	case STATE_HEADER_SPACE:
  		if (ev.pulse)
  			break;
  
  		if (eq_margin(ev.duration, NEC_HEADER_SPACE, NEC_UNIT)) {
  			data->state = STATE_BIT_PULSE;
  			return 0;
  		} else if (eq_margin(ev.duration, NEC_REPEAT_SPACE, NEC_UNIT / 2)) {
  			if (!dev->keypressed) {
  				IR_dprintk(1, "Discarding last key repeat: event after key up\n");
  			} else {
  				rc_repeat(dev);
  				IR_dprintk(1, "Repeat last key\n");
  				data->state = STATE_TRAILER_PULSE;
  			}
  			return 0;
  		}
  
  		break;
  
  	case STATE_BIT_PULSE:
  		if (!ev.pulse)
  			break;
  
  		if (!eq_margin(ev.duration, NEC_BIT_PULSE, NEC_UNIT / 2))
  			break;
  
  		data->state = STATE_BIT_SPACE;
  		return 0;
  
  	case STATE_BIT_SPACE:
  		if (ev.pulse)
  			break;
  
  		if (data->necx_repeat && data->count == NECX_REPEAT_BITS &&
  			geq_margin(ev.duration,
  			NEC_TRAILER_SPACE, NEC_UNIT / 2)) {
  				IR_dprintk(1, "Repeat last key\n");
  				rc_repeat(dev);
  				data->state = STATE_INACTIVE;
  				return 0;
  
  		} else if (data->count > NECX_REPEAT_BITS)
  			data->necx_repeat = false;
  
  		data->bits <<= 1;
  		if (eq_margin(ev.duration, NEC_BIT_1_SPACE, NEC_UNIT / 2))
  			data->bits |= 1;
  		else if (!eq_margin(ev.duration, NEC_BIT_0_SPACE, NEC_UNIT / 2))
  			break;
  		data->count++;
  
  		if (data->count == NEC_NBITS)
  			data->state = STATE_TRAILER_PULSE;
  		else
  			data->state = STATE_BIT_PULSE;
  
  		return 0;
  
  	case STATE_TRAILER_PULSE:
  		if (!ev.pulse)
  			break;
  
  		if (!eq_margin(ev.duration, NEC_TRAILER_PULSE, NEC_UNIT / 2))
  			break;
  
  		data->state = STATE_TRAILER_SPACE;
  		return 0;
  
  	case STATE_TRAILER_SPACE:
  		if (ev.pulse)
  			break;
  
  		if (!geq_margin(ev.duration, NEC_TRAILER_SPACE, NEC_UNIT / 2))
  			break;
  
  		address     = bitrev8((data->bits >> 24) & 0xff);
  		not_address = bitrev8((data->bits >> 16) & 0xff);
  		command	    = bitrev8((data->bits >>  8) & 0xff);
  		not_command = bitrev8((data->bits >>  0) & 0xff);
  
  		if ((command ^ not_command) != 0xff) {
  			IR_dprintk(1, "NEC checksum error: received 0x%08x\n",
  				   data->bits);
  			send_32bits = true;
  		}
  
  		if (send_32bits) {
  			/* NEC transport, but modified protocol, used by at
  			 * least Apple and TiVo remotes */
  			scancode = data->bits;
  			IR_dprintk(1, "NEC (modified) scancode 0x%08x\n", scancode);
  		} else {
  			/* Extended NEC */
  			scancode = address << 8  |
  				   not_address << 16 |
  				   command;
  			IR_dprintk(1, "NEC scancode 0x%06x\n", scancode);
  		}
  
  		if (data->is_nec_x)
  			data->necx_repeat = true;
  
  		rc_keydown(dev, scancode, 0);
  		data->state = STATE_INACTIVE;
  		return 0;
  	}
  
  	IR_dprintk(1, "NEC decode failed at count %d state %d (%uus %s)\n",
  		   data->count, data->state, TO_US(ev.duration), TO_STR(ev.pulse));
  	data->state = STATE_INACTIVE;
  	return -EINVAL;
  }
  
  static struct ir_raw_handler nec_handler = {
  	.protocols	= RC_BIT_NEC,
  	.decode		= ir_nec_decode,
  };
  
  static int __init ir_nec_decode_init(void)
  {
  	ir_raw_handler_register(&nec_handler);
  
  	printk(KERN_INFO "IR NEC protocol handler initialized\n");
  	return 0;
  }
  
  static void __exit ir_nec_decode_exit(void)
  {
  	ir_raw_handler_unregister(&nec_handler);
  }
  
  module_init(ir_nec_decode_init);
  module_exit(ir_nec_decode_exit);
  
  MODULE_LICENSE("GPL");
  MODULE_AUTHOR("Mauro Carvalho Chehab <mchehab@redhat.com>");
  MODULE_AUTHOR("Red Hat Inc. (http://www.redhat.com)");
  MODULE_DESCRIPTION("NEC IR protocol decoder");
  