qca_framing.c

/*====================================================================*
 *   
 *   Copyright (c) 2011, 2012, Atheros Communications Inc.
 *   
 *   Permission to use, copy, modify, and/or distribute this software 
 *   for any purpose with or without fee is hereby granted, provided 
 *   that the above copyright notice and this permission notice appear 
 *   in all copies.
 *   
 *   THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL 
 *   WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED 
 *   WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL  
 *   THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR 
 *   CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM 
 *   LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, 
 *   NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN 
 *   CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 *   
 *--------------------------------------------------------------------*/

/*====================================================================*
 *   
 *   qca_framing.c
 *
 *   Atheros ethernet framing. Every Ethernet frame is surrounded 
 *   by an atheros frame while transmitted over a serial channel;
 *
 *--------------------------------------------------------------------*/

#include <linux/kernel.h>
#include <linux/if_ether.h>

#include "qca_framing.h"

/*====================================================================*
 *   
 *   QcaFrmCreateHeader
 *
 *   Fills a provided buffer with the Atheros frame header.
 *
 *   Return: The number of bytes written in header.
 *   
 *--------------------------------------------------------------------*/

int32_t
QcaFrmCreateHeader(uint8_t *buf, uint16_t len) 
{
	len = __cpu_to_le16(len);

	buf[0] = 0xAA;
	buf[1] = 0xAA;
	buf[2] = 0xAA;
	buf[3] = 0xAA;
	buf[4] = (uint8_t)((len >> 0) & 0xFF);
	buf[5] = (uint8_t)((len >> 8) & 0xFF);
	buf[6] = 0;
	buf[7] = 0;

	return QCAFRM_HEADER_LEN;
}

/*====================================================================*
 *   
 *   QcaFrmCreateFooter
 *
 *   Fills a provided buffer with the Atheros frame footer.
 *
 * Return:   The number of bytes written in footer.
 *   
 *--------------------------------------------------------------------*/

int32_t
QcaFrmCreateFooter(uint8_t *buf) 
{
	buf[0] = 0x55;
	buf[1] = 0x55;
	return QCAFRM_FOOTER_LEN;
}


/*====================================================================*
 *   
 *   QcaFrmFsmInit
 *
 *   Initialize the framing handle. To be called at initialization for new QcaFrmHdl allocated.
 *
 *--------------------------------------------------------------------*/

void
QcaFrmFsmInit(QcaFrmHdl *frmHdl) 
{
	frmHdl->state = QCAFRM_WAIT_AA1;
}

/*====================================================================*
 *   
 *   QcaFrmFsmDecode
 *
 *   Gather received bytes and try to extract a full ethernet frame by following a simple state machine.
 *
 * Return:   QCAFRM_GATHER       No ethernet frame fully received yet.
 *           QCAFRM_NOHEAD       Header expected but not found.
 *           QCAFRM_INVLEN       Atheros frame length is invalid
 *           QCAFRM_NOTAIL       Footer expected but not found.
 *           > 0                 Number of byte in the fully received Ethernet frame
 *   
 *--------------------------------------------------------------------*/

int32_t
QcaFrmFsmDecode(QcaFrmHdl *frmHdl, uint8_t *buf, uint16_t buf_len, uint8_t recvByte) 
{
	int32_t ret = QCAFRM_GATHER;
	uint16_t len;
	switch(frmHdl->state) 
	{
	/* 4 bytes header pattern */
	case QCAFRM_WAIT_AA1:
	case QCAFRM_WAIT_AA2:
	case QCAFRM_WAIT_AA3:
	case QCAFRM_WAIT_AA4:
		if (recvByte != 0xAA) 
		{
			ret = QCAFRM_NOHEAD;
			frmHdl->state = QCAFRM_WAIT_AA1;
		}
		else 
		{
			frmHdl->state--;
		}
		break;

		/* 2 bytes length. */
		/* Borrow offset field to hold length for now. */
 	case QCAFRM_WAIT_LEN_BYTE0:
		frmHdl->offset = recvByte;
		frmHdl->state--;
		break;

	case QCAFRM_WAIT_LEN_BYTE1:
		frmHdl->offset = frmHdl->offset | (recvByte << 8);
		frmHdl->state--;
		break;

	case QCAFRM_WAIT_RSVD_BYTE1:
		frmHdl->state--;
		break;

	case QCAFRM_WAIT_RSVD_BYTE2:
		frmHdl->state--;
		len = frmHdl->offset;
		if (len > buf_len || len < QCAFRM_ETHMINLEN)
		{
			ret = QCAFRM_INVLEN;
			frmHdl->state = QCAFRM_WAIT_AA1;
		}
		else 
		{
			frmHdl->state = (QcaFrmState)(len + 1);
			/* Remaining number of bytes. */
			frmHdl->offset = 0;
		}
		break;

	default:
		/* Receiving Ethernet frame itself. */
		buf[frmHdl->offset++] = recvByte;
		frmHdl->state--;
		break;

	case QCAFRM_WAIT_551:
		if (recvByte != 0x55) 
		{
			ret = QCAFRM_NOTAIL;
			frmHdl->state = QCAFRM_WAIT_AA1;
		}
		else 
		{
			frmHdl->state--;
		}
		break;

	case QCAFRM_WAIT_552:
		if (recvByte != 0x55) 
		{
			ret = QCAFRM_NOTAIL;
			frmHdl->state = QCAFRM_WAIT_AA1;
		}
		else 
		{
			ret = frmHdl->offset;
			/* Frame is fully received. */
			frmHdl->state = QCAFRM_WAIT_AA1;
		}
		break;
	}

	return ret;
}

/*====================================================================*
 *
 *--------------------------------------------------------------------*/