vp-digi/Core/Src/kiss.c

/*
Copyright 2020-2023 Piotr Wilkon

This file is part of VP-Digi.

VP-Digi 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; either version 3 of the License, or
(at your option) any later version.

VP-Digi 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.

You should have received a copy of the GNU General Public License
along with VP-Digi.  If not, see <http://www.gnu.org/licenses/>.
*/

#include "kiss.h"
#include "ax25.h"
#include "digipeater.h"

void KissSend(Uart *port, uint8_t *buf, uint16_t size)
{
	if(port->mode == MODE_KISS)
	{
		UartSendByte(port, 0xC0);
		UartSendByte(port, 0x00);
		for(uint16_t i = 0; i < size; i++)
		{
			if(buf[i] == 0xC0) //frame end in data
			{
				UartSendByte(port, 0xDB); //frame escape
				UartSendByte(port, 0xDC); //transposed frame end
			}
			else if(buf[i] == 0xDB) //frame escape in data
			{
				UartSendByte(port, 0xDB); //frame escape
				UartSendByte(port, 0xDD); //transposed frame escape
			}
			else
				UartSendByte(port, buf[i]);
		}
		UartSendByte(port, 0xC0);
	}
}


void KissParse(Uart *port, uint8_t data)
{

	volatile uint8_t *buf = NULL;
	volatile uint16_t *index = NULL;
	if(!port->kissProcessingOngoing)
	{
		buf = port->kissBuffer;
		index = &port->kissBufferHead;
	}
	else
	{
		buf = port->kissTempBuffer;
		index = &port->kissTempBufferHead;
	}

	if(data == 0xC0) //frame end marker
	{
		if(port->kissProcessingOngoing)
		{
			*index = 0;
			return;
		}

		if(port->kissBufferHead < 16) //command+source+destination+Control=16
		{
			port->kissBufferHead = 0;
			return;
		}

		if((port->kissBuffer[0] & 0xF) != 0) //check if this is an actual frame
		{
			port->kissBufferHead = 0;
			return;
		}

		//simple sanity check
		//check if LSbits in the first 13 bytes are set to 0
		//they should always be in an AX.25 frame
		for(uint8_t i = 0; i < 13; i++)
		{
			if((port->kissBuffer[i + 1] & 1) != 0)
			{
				port->kissBufferHead = 0;
				return;
			}
		}

		uint16_t pathEnd = 0;

		//find path end bit (C-bit)
		for(uint16_t i = 0; i < port->kissBufferHead; i++)
		{
			if((port->kissBuffer[i + 1] & 1) != 0)
			{
				pathEnd = i + 1;
				break;
			}
		}

		//C-bit must lay on a 7 byte boundary (every path element is 7 bytes long)
		if(pathEnd % 7)
		{
			port->kissBufferHead = 0;
			return;
		}


		__disable_irq();
		port->kissProcessingOngoing = 1;
		port->kissTempBufferHead = 0;
		__enable_irq();
		port->rxType = DATA_KISS;
		return;
	}
	else if(*index > 0)
	{
		if((data == 0xDC) && (buf[*index - 1] == 0xDB)) //escape character with transposed frame end
		{
			buf[*index - 1] = 0xC0;
			return;
		}
		else if((data == 0xDD) && (buf[*index - 1] == 0xDB)) //escape character with transposed escape character
		{
			buf[*index - 1] = 0xDB;
			return;
		}
	}
	buf[(*index)++] = data;

	if(!port->kissProcessingOngoing)
		port->kissBufferHead %= sizeof(port->kissBuffer);
	else
		port->kissTempBufferHead %= sizeof(port->kissTempBuffer);
}

void KissProcess(Uart *port)
{
	if(port->rxType == DATA_KISS)
	{
		Ax25WriteTxFrame((uint8_t*)&port->kissBuffer[1], port->kissBufferHead - 1);
		DigiStoreDeDupe((uint8_t*)&port->kissBuffer[1], port->kissBufferHead - 1);
		port->kissBufferHead = 0;
		__disable_irq();
		port->kissProcessingOngoing = 0;
		if(port->kissTempBufferHead > 0)
		{
			memcpy((uint8_t*)port->kissBuffer, (uint8_t*)port->kissTempBuffer, port->kissTempBufferHead);
			port->kissBufferHead = port->kissTempBufferHead;
			port->kissTempBufferHead = 0;
		}
		__enable_irq();
		port->rxType = DATA_NOTHING;
	}
}