text: /* ir-sharp-decoder.c - handle Sharp IR Pulse/Space protocol
   *
   * Copyright (C) 2013-2014 Imagination Technologies Ltd.
   *
   * Based on NEC decoder:
   * Copyright (C) 2010 by Mauro Carvalho Chehab
   *
   * 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 SHARP_NBITS		15
  #define SHARP_UNIT		40000  /* ns */
  #define SHARP_BIT_PULSE		(8    * SHARP_UNIT) /* 320us */
  #define SHARP_BIT_0_PERIOD	(25   * SHARP_UNIT) /* 1ms (680us space) */
  #define SHARP_BIT_1_PERIOD	(50   * SHARP_UNIT) /* 2ms (1680ms space) */
  #define SHARP_ECHO_SPACE	(1000 * SHARP_UNIT) /* 40 ms */
  #define SHARP_TRAILER_SPACE	(125  * SHARP_UNIT) /* 5 ms (even longer) */
  
  enum sharp_state {
  	STATE_INACTIVE,
  	STATE_BIT_PULSE,
  	STATE_BIT_SPACE,
  	STATE_TRAILER_PULSE,
  	STATE_ECHO_SPACE,
  	STATE_TRAILER_SPACE,
  };
  
  /**
   * ir_sharp_decode() - Decode one Sharp 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_sharp_decode(struct rc_dev *dev, struct ir_raw_event ev)
  {
  	struct sharp_dec *data = &dev->raw->sharp;
  	u32 msg, echo, address, command, scancode;
  
  	if (!rc_protocols_enabled(dev, RC_BIT_SHARP))
  		return 0;
  
  	if (!is_timing_event(ev)) {
  		if (ev.reset)
  			data->state = STATE_INACTIVE;
  		return 0;
  	}
  
  	IR_dprintk(2, "Sharp 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, SHARP_BIT_PULSE,
  			       SHARP_BIT_PULSE / 2))
  			break;
  
  		data->count = 0;
  		data->pulse_len = ev.duration;
  		data->state = STATE_BIT_SPACE;
  		return 0;
  
  	case STATE_BIT_PULSE:
  		if (!ev.pulse)
  			break;
  
  		if (!eq_margin(ev.duration, SHARP_BIT_PULSE,
  			       SHARP_BIT_PULSE / 2))
  			break;
  
  		data->pulse_len = ev.duration;
  		data->state = STATE_BIT_SPACE;
  		return 0;
  
  	case STATE_BIT_SPACE:
  		if (ev.pulse)
  			break;
  
  		data->bits <<= 1;
  		if (eq_margin(data->pulse_len + ev.duration, SHARP_BIT_1_PERIOD,
  			      SHARP_BIT_PULSE * 2))
  			data->bits |= 1;
  		else if (!eq_margin(data->pulse_len + ev.duration,
  				    SHARP_BIT_0_PERIOD, SHARP_BIT_PULSE * 2))
  			break;
  		data->count++;
  
  		if (data->count == SHARP_NBITS ||
  		    data->count == SHARP_NBITS * 2)
  			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, SHARP_BIT_PULSE,
  			       SHARP_BIT_PULSE / 2))
  			break;
  
  		if (data->count == SHARP_NBITS) {
  			/* exp,chk bits should be 1,0 */
  			if ((data->bits & 0x3) != 0x2)
  				break;
  			data->state = STATE_ECHO_SPACE;
  		} else {
  			data->state = STATE_TRAILER_SPACE;
  		}
  		return 0;
  
  	case STATE_ECHO_SPACE:
  		if (ev.pulse)
  			break;
  
  		if (!eq_margin(ev.duration, SHARP_ECHO_SPACE,
  			       SHARP_ECHO_SPACE / 4))
  			break;
  
  		data->state = STATE_BIT_PULSE;
  
  		return 0;
  
  	case STATE_TRAILER_SPACE:
  		if (ev.pulse)
  			break;
  
  		if (!geq_margin(ev.duration, SHARP_TRAILER_SPACE,
  				SHARP_BIT_PULSE / 2))
  			break;
  
  		/* Validate - command, ext, chk should be inverted in 2nd */
  		msg = (data->bits >> 15) & 0x7fff;
  		echo = data->bits & 0x7fff;
  		if ((msg ^ echo) != 0x3ff) {
  			IR_dprintk(1,
  				   "Sharp checksum error: received 0x%04x, 0x%04x\n",
  				   msg, echo);
  			break;
  		}
  
  		address = bitrev8((msg >> 7) & 0xf8);
  		command = bitrev8((msg >> 2) & 0xff);
  
  		scancode = address << 8 | command;
  		IR_dprintk(1, "Sharp scancode 0x%04x\n", scancode);
  
  		rc_keydown(dev, scancode, 0);
  		data->state = STATE_INACTIVE;
  		return 0;
  	}
  
  	IR_dprintk(1, "Sharp 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 sharp_handler = {
  	.protocols	= RC_BIT_SHARP,
  	.decode		= ir_sharp_decode,
  };
  
  static int __init ir_sharp_decode_init(void)
  {
  	ir_raw_handler_register(&sharp_handler);
  
  	pr_info("IR Sharp protocol handler initialized\n");
  	return 0;
  }
  
  static void __exit ir_sharp_decode_exit(void)
  {
  	ir_raw_handler_unregister(&sharp_handler);
  }
  
  module_init(ir_sharp_decode_init);
  module_exit(ir_sharp_decode_exit);
  
  MODULE_LICENSE("GPL");
  MODULE_AUTHOR("James Hogan <james.hogan@imgtec.com>");
  MODULE_DESCRIPTION("Sharp IR protocol decoder");
  