/* 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 "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;

        if (!(dev->raw->enabled_protocols & RC_TYPE_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 / 2)) {
                        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);
                        break;
                }

                if ((address ^ not_address) != 0xff) {
                        /* Extended NEC */
                        scancode = address     << 16 |
                                   not_address <<  8 |
                                   command;
                        IR_dprintk(1, "NEC (Ext) scancode 0x%06x\n", scancode);
                } else {
                        /* Normal NEC */
                        scancode = address << 8 | command;
                        IR_dprintk(1, "NEC scancode 0x%04x\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 state %d (%uus %s)\n",
                   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_TYPE_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");