canframelen.c

/*
 * canframelen.c
 *
 * Copyright (c) 2013, 2014 Czech Technical University in Prague
 *
 * Author: Michal Sojka <sojkam1@fel.cvut.cz>
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. Neither the name of Czech Technical University in Prague nor the
 *    names of its contributors may be used to endorse or promote
 *    products derived from this software without specific prior
 *    written permission.
 *
 * Alternatively, provided that this notice is retained in full, this
 * software may be distributed under the terms of the GNU General
 * Public License ("GPL") version 2, in which case the provisions of the
 * GPL apply INSTEAD OF those given above.
 *
 * The provided data structures and external interfaces from this code
 * are not restricted to be used by modules with a GPL compatible license.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
 * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH
 * DAMAGE.
 *
 * Send feedback to <linux-can@vger.kernel.org>
 *
 */

#include "canframelen.h"
#include <stdint.h>
#include <stddef.h>
#include <stdbool.h>
#include <string.h>
#include <assert.h>
#include <arpa/inet.h>

/**
 * Functions and types for CRC checks.
 *
 * Generated on Wed Jan  8 15:14:20 2014,
 * by pycrc v0.8.1, http://www.tty1.net/pycrc/
 * using the configuration:
 *    Width        = 15
 *    Poly         = 0x4599
 *    XorIn        = 0x0000
 *    ReflectIn    = False
 *    XorOut       = 0x0000
 *    ReflectOut   = False
 *    Algorithm    = table-driven
 *****************************************************************************/

typedef uint16_t crc_t;

/**
 * Static table used for the table_driven implementation.
 *****************************************************************************/
static const crc_t crc_table[256] = {
	0x0000, 0x4599, 0x4eab, 0x0b32, 0x58cf, 0x1d56, 0x1664, 0x53fd, 0x7407, 0x319e, 0x3aac, 0x7f35, 0x2cc8, 0x6951, 0x6263, 0x27fa,
	0x2d97, 0x680e, 0x633c, 0x26a5, 0x7558, 0x30c1, 0x3bf3, 0x7e6a, 0x5990, 0x1c09, 0x173b, 0x52a2, 0x015f, 0x44c6, 0x4ff4, 0x0a6d,
	0x5b2e, 0x1eb7, 0x1585, 0x501c, 0x03e1, 0x4678, 0x4d4a, 0x08d3, 0x2f29, 0x6ab0, 0x6182, 0x241b, 0x77e6, 0x327f, 0x394d, 0x7cd4,
	0x76b9, 0x3320, 0x3812, 0x7d8b, 0x2e76, 0x6bef, 0x60dd, 0x2544, 0x02be, 0x4727, 0x4c15, 0x098c, 0x5a71, 0x1fe8, 0x14da, 0x5143,
	0x73c5, 0x365c, 0x3d6e, 0x78f7, 0x2b0a, 0x6e93, 0x65a1, 0x2038, 0x07c2, 0x425b, 0x4969, 0x0cf0, 0x5f0d, 0x1a94, 0x11a6, 0x543f,
	0x5e52, 0x1bcb, 0x10f9, 0x5560, 0x069d, 0x4304, 0x4836, 0x0daf, 0x2a55, 0x6fcc, 0x64fe, 0x2167, 0x729a, 0x3703, 0x3c31, 0x79a8,
	0x28eb, 0x6d72, 0x6640, 0x23d9, 0x7024, 0x35bd, 0x3e8f, 0x7b16, 0x5cec, 0x1975, 0x1247, 0x57de, 0x0423, 0x41ba, 0x4a88, 0x0f11,
	0x057c, 0x40e5, 0x4bd7, 0x0e4e, 0x5db3, 0x182a, 0x1318, 0x5681, 0x717b, 0x34e2, 0x3fd0, 0x7a49, 0x29b4, 0x6c2d, 0x671f, 0x2286,
	0x2213, 0x678a, 0x6cb8, 0x2921, 0x7adc, 0x3f45, 0x3477, 0x71ee, 0x5614, 0x138d, 0x18bf, 0x5d26, 0x0edb, 0x4b42, 0x4070, 0x05e9,
	0x0f84, 0x4a1d, 0x412f, 0x04b6, 0x574b, 0x12d2, 0x19e0, 0x5c79, 0x7b83, 0x3e1a, 0x3528, 0x70b1, 0x234c, 0x66d5, 0x6de7, 0x287e,
	0x793d, 0x3ca4, 0x3796, 0x720f, 0x21f2, 0x646b, 0x6f59, 0x2ac0, 0x0d3a, 0x48a3, 0x4391, 0x0608, 0x55f5, 0x106c, 0x1b5e, 0x5ec7,
	0x54aa, 0x1133, 0x1a01, 0x5f98, 0x0c65, 0x49fc, 0x42ce, 0x0757, 0x20ad, 0x6534, 0x6e06, 0x2b9f, 0x7862, 0x3dfb, 0x36c9, 0x7350,
	0x51d6, 0x144f, 0x1f7d, 0x5ae4, 0x0919, 0x4c80, 0x47b2, 0x022b, 0x25d1, 0x6048, 0x6b7a, 0x2ee3, 0x7d1e, 0x3887, 0x33b5, 0x762c,
	0x7c41, 0x39d8, 0x32ea, 0x7773, 0x248e, 0x6117, 0x6a25, 0x2fbc, 0x0846, 0x4ddf, 0x46ed, 0x0374, 0x5089, 0x1510, 0x1e22, 0x5bbb,
	0x0af8, 0x4f61, 0x4453, 0x01ca, 0x5237, 0x17ae, 0x1c9c, 0x5905, 0x7eff, 0x3b66, 0x3054, 0x75cd, 0x2630, 0x63a9, 0x689b, 0x2d02,
	0x276f, 0x62f6, 0x69c4, 0x2c5d, 0x7fa0, 0x3a39, 0x310b, 0x7492, 0x5368, 0x16f1, 0x1dc3, 0x585a, 0x0ba7, 0x4e3e, 0x450c, 0x0095
};

/**
 * Update the crc value with new data.
 *
 * \param crc      The current crc value.
 * \param data     Pointer to a buffer of \a data_len bytes.
 * \param data_len Number of bytes in the \a data buffer.
 * \return         The updated crc value.
 *****************************************************************************/
static crc_t crc_update_bytewise(crc_t crc, const unsigned char *data, size_t data_len)
{
	unsigned int tbl_idx;

	while (data_len--) {
		tbl_idx = ((crc >> 7) ^ *data) & 0xff;
		crc = (crc_table[tbl_idx] ^ (crc << 8)) & 0x7fff;

		data++;
	}
	return crc & 0x7fff;
}

/**
 * Update the crc value with new data.
 *
 * \param crc      The current crc value.
 * \param data     Data value
 * \param bits	   The number of most significant bits in data used for CRC calculation
 * \return         The updated crc value.
 *****************************************************************************/
static crc_t crc_update_bitwise(crc_t crc, uint8_t data, size_t bits)
{
	uint8_t i;
	bool bit;

	for (i = 0x80; bits--; i >>= 1) {
		bit = crc & 0x4000;
		if (data & i) {
			bit = !bit;
		}
		crc <<= 1;
		if (bit) {
			crc ^= 0x4599;
		}
	}
	return crc & 0x7fff;
}

static crc_t calc_bitmap_crc(uint8_t *bitmap, unsigned start, unsigned end)
{
	crc_t crc = 0;

	if (start % 8) {
		crc = crc_update_bitwise(crc, bitmap[start / 8] << (start % 8), 8 - start % 8);
		start += 8 - start % 8;
	}
	crc = crc_update_bytewise(crc, &bitmap[start / 8], (end - start) / 8);
	crc = crc_update_bitwise(crc, bitmap[end / 8], end % 8);
	return crc;
}

static unsigned cfl_exact(struct can_frame *frame)
{
	uint8_t bitmap[16];
	unsigned start = 0, end;
	crc_t crc;
	uint16_t crc_be;
	uint8_t mask, lookfor;
	unsigned i, stuffed;
	const int8_t clz[32] = /* count of leading zeros in 5 bit numbers */
		{ 5, 4, 3, 3, 2, 2, 2, 2, 1, 1, 1, 1, 1, 1, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 };

	/* Prepare bitmap */
	memset(bitmap, 0, sizeof(bitmap));
	if (frame->can_id & CAN_EFF_FLAG) {
		/* bit            7      0 7      0 7      0 7      0
		 * bitmap[0-3]   |.sBBBBBB BBBBBSIE EEEEEEEE EEEEEEEE| s = SOF, B = Base ID (11 bits), S = SRR, I = IDE, E = Extended ID (18 bits)
		 * bitmap[4-7]   |ER10DLC4 00000000 11111111 22222222| R = RTR, 0 = r0, 1 = r1, DLC4 = DLC, Data bytes
		 * bitmap[8-11]  |33333333 44444444 55555555 66666666| Data bytes
		 * bitmap[12-15] |77777777 ........ ........ ........| Data bytes
		 */
		bitmap[0] = (frame->can_id & CAN_EFF_MASK) >> 23;
		bitmap[1] = ((frame->can_id >> 18) & 0x3f) << 3 |
			    3 << 1	       	     	      	| /* SRR, IDE */
			    ((frame->can_id >> 17) & 0x01);
		bitmap[2] = (frame->can_id >> 9) & 0xff;
		bitmap[3] = (frame->can_id >> 1) & 0xff;
		bitmap[4] = (frame->can_id & 0x1) << 7              |
			    (!!(frame->can_id & CAN_RTR_FLAG)) << 6 |
			    0 << 4	      		       	    | /* r1, r0 */
			    (frame->can_dlc & 0xf);
		memcpy(&bitmap[5], &frame->data, frame->can_dlc);
		start = 1;
		end = 40 + 8*frame->can_dlc;
	} else {
		/* bit           7      0 7      0 7      0 7      0
		 * bitmap[0-3]  |.....sII IIIIIIII IRE0DLC4 00000000| s = SOF, I = ID (11 bits), R = RTR, E = IDE, DLC4 = DLC
		 * bitmap[4-7]  |11111111 22222222 33333333 44444444| Data bytes
		 * bitmap[8-11] |55555555 66666666 77777777 ........| Data bytes
		 */
		bitmap[0] = (frame->can_id & CAN_SFF_MASK) >> 9;
		bitmap[1] = (frame->can_id >> 1) & 0xff;
		bitmap[2] = ((frame->can_id << 7) & 0xff) |
			    (!!(frame->can_id & CAN_RTR_FLAG)) << 6 |
			    0 << 4 | /* IDE, r0 */
			    (frame->can_dlc & 0xf);
		memcpy(&bitmap[3], &frame->data, frame->can_dlc);
		start = 5;
		end = 24 + 8 * frame->can_dlc;
	}

	/* Calc and append CRC */
	crc = calc_bitmap_crc(bitmap, start, end);
	crc_be = htons(crc << 1);
	assert(end % 8 == 0);
	memcpy(bitmap + end / 8, &crc_be, 2);
	end += 15;

	/* Count stuffed bits */
	mask 	= 0x1f;
	lookfor = 0;
	i 	= start;
	stuffed = 0;
	while (i < end) {
		unsigned change;
		unsigned bits = (bitmap[i / 8] << 8 | bitmap[i / 8 + 1]) >> (16 - 5 - i % 8);
		lookfor = lookfor ? 0 : mask; /* We alternate between looking for a series of zeros or ones */
		change = (bits & mask) ^ lookfor; /* 1 indicates a change */
		if (change) { /* No bit was stuffed here */
			i += clz[change];
			mask = 0x1f; /* Next look for 5 same bits */
		} else {
			i += (mask == 0x1f) ? 5 : 4;
			if (i <= end) {
				stuffed++;
				mask = 0x1e; /* Next look for 4 bits (5th bit is the stuffed one) */
			}
		}
	}
	return end - start + stuffed +
		3 + 		/* CRC del, ACK, ACK del */
		7 +		/* EOF */
		3;		/* IFS */
}


unsigned can_frame_length(struct canfd_frame *frame, enum cfl_mode mode, int mtu)
{
	int eff = (frame->can_id & CAN_EFF_FLAG);

	if (mtu != CAN_MTU)
		return 0;	/* CANFD is not supported yet */

	switch (mode) {
	case CFL_NO_BITSTUFFING:
		return (eff ? 67 : 47) + frame->len * 8;
	case CFL_WORSTCASE:
		return (eff ? 80 : 55) + frame->len * 10;
	case CFL_EXACT:
		return cfl_exact((struct can_frame*)frame);
	}
	return 0; /* Unknown mode */
}