ISComm.c

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/*
MIT LICENSE

Copyright (c) 2014-2021 Inertial Sense, Inc. - http://inertialsense.com

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files(the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions :

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
*/

#include "ISComm.h"

unsigned int calculate24BitCRCQ(unsigned char* buffer, unsigned int len)
{
        static const unsigned int TABLE_CRC24Q[] =
        {
                0x000000,0x864CFB,0x8AD50D,0x0C99F6,0x93E6E1,0x15AA1A,0x1933EC,0x9F7F17,
                0xA18139,0x27CDC2,0x2B5434,0xAD18CF,0x3267D8,0xB42B23,0xB8B2D5,0x3EFE2E,
                0xC54E89,0x430272,0x4F9B84,0xC9D77F,0x56A868,0xD0E493,0xDC7D65,0x5A319E,
                0x64CFB0,0xE2834B,0xEE1ABD,0x685646,0xF72951,0x7165AA,0x7DFC5C,0xFBB0A7,
                0x0CD1E9,0x8A9D12,0x8604E4,0x00481F,0x9F3708,0x197BF3,0x15E205,0x93AEFE,
                0xAD50D0,0x2B1C2B,0x2785DD,0xA1C926,0x3EB631,0xB8FACA,0xB4633C,0x322FC7,
                0xC99F60,0x4FD39B,0x434A6D,0xC50696,0x5A7981,0xDC357A,0xD0AC8C,0x56E077,
                0x681E59,0xEE52A2,0xE2CB54,0x6487AF,0xFBF8B8,0x7DB443,0x712DB5,0xF7614E,
                0x19A3D2,0x9FEF29,0x9376DF,0x153A24,0x8A4533,0x0C09C8,0x00903E,0x86DCC5,
                0xB822EB,0x3E6E10,0x32F7E6,0xB4BB1D,0x2BC40A,0xAD88F1,0xA11107,0x275DFC,
                0xDCED5B,0x5AA1A0,0x563856,0xD074AD,0x4F0BBA,0xC94741,0xC5DEB7,0x43924C,
                0x7D6C62,0xFB2099,0xF7B96F,0x71F594,0xEE8A83,0x68C678,0x645F8E,0xE21375,
                0x15723B,0x933EC0,0x9FA736,0x19EBCD,0x8694DA,0x00D821,0x0C41D7,0x8A0D2C,
                0xB4F302,0x32BFF9,0x3E260F,0xB86AF4,0x2715E3,0xA15918,0xADC0EE,0x2B8C15,
                0xD03CB2,0x567049,0x5AE9BF,0xDCA544,0x43DA53,0xC596A8,0xC90F5E,0x4F43A5,
                0x71BD8B,0xF7F170,0xFB6886,0x7D247D,0xE25B6A,0x641791,0x688E67,0xEEC29C,
                0x3347A4,0xB50B5F,0xB992A9,0x3FDE52,0xA0A145,0x26EDBE,0x2A7448,0xAC38B3,
                0x92C69D,0x148A66,0x181390,0x9E5F6B,0x01207C,0x876C87,0x8BF571,0x0DB98A,
                0xF6092D,0x7045D6,0x7CDC20,0xFA90DB,0x65EFCC,0xE3A337,0xEF3AC1,0x69763A,
                0x578814,0xD1C4EF,0xDD5D19,0x5B11E2,0xC46EF5,0x42220E,0x4EBBF8,0xC8F703,
                0x3F964D,0xB9DAB6,0xB54340,0x330FBB,0xAC70AC,0x2A3C57,0x26A5A1,0xA0E95A,
                0x9E1774,0x185B8F,0x14C279,0x928E82,0x0DF195,0x8BBD6E,0x872498,0x016863,
                0xFAD8C4,0x7C943F,0x700DC9,0xF64132,0x693E25,0xEF72DE,0xE3EB28,0x65A7D3,
                0x5B59FD,0xDD1506,0xD18CF0,0x57C00B,0xC8BF1C,0x4EF3E7,0x426A11,0xC426EA,
                0x2AE476,0xACA88D,0xA0317B,0x267D80,0xB90297,0x3F4E6C,0x33D79A,0xB59B61,
                0x8B654F,0x0D29B4,0x01B042,0x87FCB9,0x1883AE,0x9ECF55,0x9256A3,0x141A58,
                0xEFAAFF,0x69E604,0x657FF2,0xE33309,0x7C4C1E,0xFA00E5,0xF69913,0x70D5E8,
                0x4E2BC6,0xC8673D,0xC4FECB,0x42B230,0xDDCD27,0x5B81DC,0x57182A,0xD154D1,
                0x26359F,0xA07964,0xACE092,0x2AAC69,0xB5D37E,0x339F85,0x3F0673,0xB94A88,
                0x87B4A6,0x01F85D,0x0D61AB,0x8B2D50,0x145247,0x921EBC,0x9E874A,0x18CBB1,
                0xE37B16,0x6537ED,0x69AE1B,0xEFE2E0,0x709DF7,0xF6D10C,0xFA48FA,0x7C0401,
                0x42FA2F,0xC4B6D4,0xC82F22,0x4E63D9,0xD11CCE,0x575035,0x5BC9C3,0xDD8538
        };

        unsigned int crc = 0;
        for (uint32_t i = 0; i != len; i++)
        {
                crc = ((crc << 8) & 0xFFFFFF) ^ TABLE_CRC24Q[(crc >> 16) ^ buffer[i]];
        }
        return crc;
}

unsigned int getBitsAsUInt32(const unsigned char* buffer, unsigned int pos, unsigned int len)
{
        unsigned int bits = 0;
        for (unsigned int i = pos; i < pos + len; i++)
        {
                bits = (bits << 1) + ((buffer[i / 8] >> (7 - i % 8)) & 1u);
        }
        return bits;
}

const unsigned int g_validBaudRates[IS_BAUDRATE_COUNT] = { IS_BAUDRATE_3000000, IS_BAUDRATE_921600, IS_BAUDRATE_460800, IS_BAUDRATE_230400, IS_BAUDRATE_115200, IS_BAUDRATE_57600, IS_BAUDRATE_38400, IS_BAUDRATE_19200, IS_BAUDRATE_9600 };
static int s_packetEncodingEnabled = 1;

// Replace special character with encoded equivalent and add to buffer
static uint8_t* encodeByteAddToBuffer(uint32_t val, uint8_t* ptrDest)
{
        switch (val)
        {
        case PSC_ASCII_START_BYTE:
        case PSC_ASCII_END_BYTE:
        case PSC_START_BYTE:
        case PSC_END_BYTE:
        case PSC_RESERVED_KEY:
        case UBLOX_START_BYTE1:
        case RTCM3_START_BYTE:
                if (s_packetEncodingEnabled)
                {
                        *ptrDest++ = PSC_RESERVED_KEY;
                        *ptrDest++ = (uint8_t)~val;
                }
                else
                {
                        *ptrDest++ = (uint8_t)val;
                }
                break;
        default:
                *ptrDest++ = (uint8_t)val;
                break;
        }

        return ptrDest;
}

static int dataIdShouldSwap(uint32_t dataId)
{
        switch (dataId)
        {
        case DID_GPS1_VERSION:
        case DID_GPS2_VERSION:
                return 0;
        }
        return 1;
}

static void swapPacket(packet_t* pkt)
{
        if (pkt->hdr.flags & CM_PKT_FLAGS_RAW_DATA_NO_SWAP)
        {
                if ((pkt->hdr.pid == PID_DATA || pkt->hdr.pid == PID_SET_DATA) && pkt->body.size >= sizeof(p_data_hdr_t))
                {
                        // swap the data header only
                        flipEndianess32(pkt->body.ptr, sizeof(p_data_hdr_t));
                }
        }
        else if (pkt->body.size < sizeof(p_data_hdr_t) || (pkt->hdr.pid != PID_DATA && pkt->hdr.pid != PID_SET_DATA))
        {
                // swap entire packet, not a data packet
                flipEndianess32(pkt->body.ptr, pkt->body.size);
        }
        else
        {
                // swap header
                flipEndianess32(pkt->body.ptr, sizeof(p_data_hdr_t));

                // get header
                p_data_hdr_t* dataHdr = (p_data_hdr_t*)pkt->body.ptr;

                // if dev_info_t, swap only the uint32 fields, this data structure is handled special as it contains char[] arrays and uint32_t in the same struct
                if (dataHdr->id == DID_DEV_INFO && pkt->body.size == sizeof(p_data_hdr_t) + sizeof(dev_info_t))
                {
                        // swap only the pieces that need swapping
                        dev_info_t* devInfo = (dev_info_t*)(pkt->body.ptr + sizeof(p_data_hdr_t));
                        devInfo->buildNumber = SWAP32(devInfo->buildNumber);
                        devInfo->repoRevision = SWAP32(devInfo->repoRevision);
                        devInfo->serialNumber = SWAP32(devInfo->serialNumber);
                }
                else if (dataIdShouldSwap(dataHdr->id))
                {
                        // swap entire packet body
                        flipEndianess32(pkt->body.ptr + sizeof(p_data_hdr_t), pkt->body.size - sizeof(p_data_hdr_t));

                        // flip doubles
                        uint16_t* offsets;
                        uint16_t offsetsLength;
                        uint8_t* dataBuf = pkt->body.ptr + sizeof(p_data_hdr_t);

                        // flip doubles back if needed
                        if ((offsets = getDoubleOffsets(dataHdr->id, &offsetsLength)))
                        {
                                flipDoubles(dataBuf, dataHdr->size, dataHdr->offset, offsets, offsetsLength);
                        }

                        // flip strings back if needed
                        if ((offsets = getStringOffsetsLengths(dataHdr->id, &offsetsLength)))
                        {
                                flipStrings(dataBuf, dataHdr->size, dataHdr->offset, offsets, offsetsLength);
                        }
                }
        }
}

void is_comm_init(is_comm_instance_t* instance, uint8_t *buffer, int bufferSize)
{
        // Clear buffer and initialize buffer pointers
        memset(buffer, 0, bufferSize);
        instance->buf.size = bufferSize;
        instance->buf.start = buffer;
        instance->buf.end = buffer + bufferSize;
        instance->buf.head = instance->buf.tail = instance->buf.scan = buffer;
        
        // Set parse enable flags
        instance->config.enableISB = 1;
        instance->config.enableASCII = 1;
        instance->config.enableUblox = 1;
        instance->config.enableRTCM3 = 1;
        
        instance->txPktCount = 0;
        instance->rxErrorCount = 0;
        instance->hasStartByte = 0;
        memset(&instance->dataHdr, 0, sizeof(p_data_hdr_t));
        instance->dataPtr = instance->buf.start;
    instance->ackNeeded = 0;
        memset(&instance->pkt, 0, sizeof(packet_t));
        instance->pkt.body.ptr = instance->buf.start;
        instance->pkt.body.size = 0;
        instance->altDecodeBuf = NULL;
}

static __inline void reset_parser(is_comm_instance_t *instance)
{
        instance->hasStartByte = 0;
        instance->buf.head = instance->buf.scan;
}

static protocol_type_t processInertialSensePkt(is_comm_instance_t* instance)
{
        // Packet to decode into
        packet_t *pkt = &(instance->pkt);
        int pktSize = (int)(instance->buf.scan - instance->buf.head);
        uint8_t* head;

        // Set location where to decode packet. 
        if(instance->altDecodeBuf)
        {       // Decode to alternate buffer
                memcpy(instance->altDecodeBuf, instance->buf.head, pktSize);
                head = pkt->body.ptr = instance->altDecodeBuf;
        }
        else
        {       // Decode packet in place on top of the receive buffer to save memory
                head = instance->buf.head;
                instance->pkt.body.ptr = instance->buf.start;
        }

        instance->pktPtr = instance->buf.head;
        reset_parser(instance);

        if (is_decode_binary_packet(pkt, head, pktSize) == 0)
        {
                instance->ackNeeded = 0;
                instance->dataPtr = NULL;

        switch(pkt->hdr.pid)
        {
                case PID_SET_DATA:
                case PID_DATA:
                        instance->dataHdr = *((p_data_hdr_t*)pkt->body.ptr);

                        // ensure offset and size are in bounds - check the size independent of offset because the size could be a
                        //  negative number in case of corrupt data
                        if (instance->dataHdr.id > DID_NULL &&
//                              instance->dataHdr.id < DID_COUNT &&             // Commented out to allow support for Luna EVB data sets
                                instance->dataHdr.size <= MAX_DATASET_SIZE //&&
//                                      instance->dataHdr.offset <= MAX_DATASET_SIZE &&
//                                      instance->dataHdr.offset + instance->dataHdr.size <= MAX_DATASET_SIZE
                                )
                        {
                                if(pkt->hdr.pid==PID_SET_DATA)
                                {       // acknowledge valid data received
                                        instance->ackNeeded = PID_ACK;
                                }
                                        
                                // Update data pointer
                                instance->dataPtr = pkt->body.ptr + sizeof(p_data_hdr_t);
                                return _PTYPE_INERTIAL_SENSE_DATA;
                        }
                        else
                        {       // negative acknowledge data received
                                instance->ackNeeded = PID_NACK;
                        }
            break;
                
        case PID_GET_DATA:
            // copy the requested data set info
                        instance->dataHdr = *((p_data_hdr_t*)pkt->body.ptr);
                        return _PTYPE_INERTIAL_SENSE_CMD;
                case PID_STOP_BROADCASTS_ALL_PORTS:
                case PID_STOP_DID_BROADCAST:
                case PID_STOP_BROADCASTS_CURRENT_PORT:
                        return _PTYPE_INERTIAL_SENSE_CMD;
                case PID_ACK:
                case PID_NACK:
                        return _PTYPE_INERTIAL_SENSE_ACK;
        }                    
        }

        // Invalid data or checksum failure.
        instance->rxErrorCount++;
        return _PTYPE_PARSE_ERROR;
}

static protocol_type_t processAsciiPkt(is_comm_instance_t* instance)
{
        uint8_t* head = instance->buf.head;
        reset_parser(instance);

        // calculate checksum, if pass return special data id
        if (instance->buf.scan - head > 7)
        {
                // parse out checksum, put in temp null terminator
                uint8_t tmp = *(instance->buf.scan - 2);
                *(instance->buf.scan - 2) = 0;
                int actualCheckSum = (int)strtol((const char*)instance->buf.scan - 4, 0, 16);
                *(instance->buf.scan - 2) = tmp;
                int dataCheckSum = 0;
                for (uint8_t* ptr = head + 1, *ptrEnd = instance->buf.scan - 5; ptr < ptrEnd; ptr++)
                {
                        dataCheckSum ^= (int)*ptr;
                }
                if (actualCheckSum == dataCheckSum)
                {       // valid ASCII Data
                        // Update data pointer and info
                        instance->dataPtr = instance->pktPtr = head;
                        instance->dataHdr.id = 0;
                        instance->dataHdr.size = (uint32_t)(instance->buf.scan - head);
                        instance->dataHdr.offset = 0;
                        return _PTYPE_ASCII_NMEA;
                }
        }

        // Invalid data or checksum failure.
        instance->rxErrorCount++;
        return _PTYPE_PARSE_ERROR;
}

static protocol_type_t processUbloxByte(is_comm_instance_t* instance)
{
        switch (instance->parseState)
        {
        case 1: // preamble 2
                if (*(instance->buf.scan - 1) != UBLOX_START_BYTE2)
                {
                        // corrupt data
                        instance->rxErrorCount++;
                        reset_parser(instance);
                        return _PTYPE_PARSE_ERROR;
                }
                // fall through
        case 2: // class id
                // fall through
        case 3: // message id
                // fall through
        case 4: // length byte 1
                // fall through
        case 0:
                instance->parseState++;
                break;

        case 5: // length byte 2
                {
                        uint32_t len = BE_SWAP16(*((uint16_t*)(void*)(instance->buf.scan - 2)));

                        // if length is greater than available buffer, we cannot parse this ublox packet - ublox header is 6 bytes
                        if (len > instance->buf.size - 6)
                        {
                                instance->rxErrorCount++;
                                reset_parser(instance);
                                return _PTYPE_PARSE_ERROR;
                        }
                        instance->parseState = -((int32_t)len + 2);
                } 
                break;

        default:
                if (++instance->parseState == 0)
                {
                        // end of ublox packet, if checksum passes, send the external id
                        instance->hasStartByte = 0;
                        uint8_t actualChecksum1 = *(instance->buf.scan - 2);
                        uint8_t actualChecksum2 = *(instance->buf.scan - 1);
                        uint8_t calcChecksum1 = 0;
                        uint8_t calcChecksum2 = 0;

                        // calculate checksum, skipping the first two preamble bytes and the last two bytes which are the checksum
                        for (uint8_t* ptr = instance->buf.head + 2, *ptrEnd = instance->buf.scan - 2; ptr < ptrEnd; ptr++)
                        {
                                calcChecksum1 += *ptr;
                                calcChecksum2 += calcChecksum1;
                        }
                        if (actualChecksum1 == calcChecksum1 && actualChecksum2 == calcChecksum2)
                        {       // Checksum passed - Valid ublox packet
                                // Update data pointer and info
                                instance->dataPtr = instance->buf.head;
                                instance->dataHdr.id = 0;
                                instance->dataHdr.size = (uint32_t)(instance->buf.scan - instance->buf.head);
                                instance->dataHdr.offset = 0;
                                instance->pktPtr = instance->buf.head;
                                reset_parser(instance);
                                return _PTYPE_UBLOX;
                        }
                        else
                        {       // Checksum failure
                                instance->rxErrorCount++;
                                reset_parser(instance);
                                return _PTYPE_PARSE_ERROR;
                        }
                }
        }

        return _PTYPE_NONE;
}

static protocol_type_t processRtcm3Byte(is_comm_instance_t* instance)
{
        switch (instance->parseState)
        {
        case 0:
        case 1:
                instance->parseState++;
                break;

        case 2:
        {
        uint32_t msgLength = getBitsAsUInt32(instance->buf.head, 14, 10);

                // if message is too small or too big for rtcm3 or too big for buffer, fail
                if (msgLength > 1023 || msgLength > instance->buf.size - 6)
                {
                        // corrupt data
                        instance->rxErrorCount++;
                        reset_parser(instance);
                        return _PTYPE_PARSE_ERROR;
                }

                // parse the message plus 3 crc24 bytes
        instance->parseState = -((int32_t)msgLength + 3);
        } break;

        default:
                if (++instance->parseState == 0)
                {
                        // get len without 3 crc bytes
            int lenWithoutCrc = (int)((instance->buf.scan - instance->buf.head) - 3);
                        uint32_t actualCRC = calculate24BitCRCQ(instance->buf.head, lenWithoutCrc);
                        uint32_t correctCRC = getBitsAsUInt32(instance->buf.head + lenWithoutCrc, 0, 24);

                        if (actualCRC == correctCRC)
                        {       // Checksum passed - Valid RTCM3 packet
                                // Update data pointer and info
                                instance->dataPtr = instance->buf.head;
                                instance->dataHdr.id = 0;
                                instance->dataHdr.size = (uint32_t)(instance->buf.scan - instance->buf.head);
                                instance->dataHdr.offset = 0;
                                instance->pktPtr = instance->buf.head;
                                reset_parser(instance);
                                return _PTYPE_RTCM3;
                        }
                        else
                        {       // Checksum failure
                                instance->rxErrorCount++;
                                reset_parser(instance);
                                return _PTYPE_PARSE_ERROR;
                        }
                }
        }

        return _PTYPE_NONE;
}

int is_comm_free(is_comm_instance_t* instance)
{
//      if (instance == 0 || instance->buf.start == 0)
//      {
//              return -1;
//      }

        is_comm_buffer_t *buf = &(instance->buf);

        int bytesFree = (int)(buf->end - buf->tail);

        // if we are out of free space, we need to either move bytes over or start over
        if (bytesFree == 0)
        {
                if ((int)(buf->head - buf->start) < (int)(buf->size / 3))       // if ring buffer start index is less than this and no space is left, clear the entire ring buffer
                {       // we will be hung unless we flush the ring buffer, we have to drop bytes in this case and the caller
                        //  will need to resend the data
                        buf->head = buf->start;
                        buf->tail = buf->start;
                        buf->scan = buf->start;
                }
                else
                {       // shift over the remaining data in the hopes that we will get a valid packet by appending the next read call
                        memmove(buf->start, buf->head, buf->tail - buf->head);
                        int shift = (int)(buf->head - buf->start);
                        buf->head -= shift;
                        buf->tail -= shift;
                        buf->scan -= shift;
                }

                // re-calculate free byte count
                bytesFree = (int)(buf->end - buf->tail);
        }

        return bytesFree;
}

protocol_type_t is_comm_parse_byte(is_comm_instance_t* instance, uint8_t byte)
{
        // Reset buffer if needed
        is_comm_free(instance);
        
        // Add byte to buffer
        *(instance->buf.tail) = byte;
        instance->buf.tail++;
        
        return is_comm_parse(instance);
}

#define FOUND_START_BYTE(init)          if(init){ instance->hasStartByte = byte; instance->buf.head = instance->buf.scan-1; }
#define START_BYTE_SEARCH_ERROR()       

protocol_type_t is_comm_parse(is_comm_instance_t* instance)
{
        is_comm_buffer_t *buf = &(instance->buf);

        // Search for packet
        while (buf->scan < buf->tail)
        {
                uint8_t byte = *(buf->scan++);

                // Check for start byte if we haven't found it yet
                if (instance->hasStartByte == 0)
                {
                        if ((byte == PSC_START_BYTE                     && instance->config.enableISB) ||
                                (byte == PSC_ASCII_START_BYTE   && instance->config.enableASCII) ||
                                (byte == UBLOX_START_BYTE1              && instance->config.enableUblox) ||
                                (byte == RTCM3_START_BYTE               && instance->config.enableRTCM3) )
                        {       // Found start byte.  Initialize states (set flag and reset pos to beginning)
                                instance->hasStartByte = byte; 
                                instance->buf.head = instance->buf.scan-1;
                                instance->parseState = 0;
                        }
                        else 
                        {       // Searching for start byte
                                if (instance->parseState != -1)
                                {
                                        instance->parseState = -1;
                                        instance->rxErrorCount++;
                                        return _PTYPE_PARSE_ERROR;      // Return to notify of error
                                }
                                continue;                                               // Continue to scan for data
                        }
                }

                // If we have a start byte, process the data type
                switch (instance->hasStartByte)
                {
                case PSC_START_BYTE:
                        if (byte == PSC_END_BYTE)
                        {
                                return processInertialSensePkt(instance);
                        }
                        break;
                case PSC_ASCII_START_BYTE:
                        if (byte == PSC_ASCII_END_BYTE)
                        {
                                return processAsciiPkt(instance);
                        }
                        //Check for invalid bytes in ASCII string and exit if found.
                        if (byte == PSC_START_BYTE || byte == PSC_END_BYTE || byte == 0)
                        {
                                instance->hasStartByte = 0;
                                instance->parseState = -1;
                                instance->rxErrorCount++;
                                return _PTYPE_PARSE_ERROR;      // Return to notify of error
                        }
                        break;
                case UBLOX_START_BYTE1:
                        if (processUbloxByte(instance) != _PTYPE_NONE)
                        {
                                return _PTYPE_UBLOX;
                        }
                        break;
                case RTCM3_START_BYTE:
                        if (processRtcm3Byte(instance) != _PTYPE_NONE)
                        {
                                return _PTYPE_RTCM3;
                        }
                }
        }

        // No valid data yet...
        return _PTYPE_NONE;
}

int is_comm_get_data(is_comm_instance_t* instance, uint32_t dataId, uint32_t offset, uint32_t size, uint32_t periodMultiple)
{
        p_data_get_t request;

        request.id = dataId;
        request.offset = offset;
        request.size = size;
        request.bc_period_multiple = periodMultiple;

        packet_hdr_t hdr;
        hdr.flags = 0;
        hdr.pid = PID_GET_DATA;
        hdr.counter = (uint8_t)instance->txPktCount++;

        return is_encode_binary_packet(&request, sizeof(request), &hdr, 0, instance->buf.start, instance->buf.size);
}

int is_comm_get_data_rmc(is_comm_instance_t* instance, uint64_t rmcBits)
{
        return  is_comm_set_data(instance, DID_RMC, offsetof(rmc_t,bits), sizeof(uint64_t), (void*)&rmcBits);
}

static int sendData(is_comm_instance_t* instance, uint32_t dataId, uint32_t offset, uint32_t size, void* data, uint32_t pid)
{
        int dataSize = size + sizeof(p_data_hdr_t);
        uint8_t toSend[MAX_DATASET_SIZE];
        if(dataSize > MAX_DATASET_SIZE)
        {
                return -1;
        }
        
        memcpy(toSend + sizeof(p_data_hdr_t), data, size);
        p_data_hdr_t* dataHdr = (p_data_hdr_t*)toSend;
        dataHdr->id = dataId;
        dataHdr->size = size;
        dataHdr->offset = offset;

        packet_hdr_t hdr;
        hdr.flags = 0;
        hdr.pid = (uint8_t)pid;
        hdr.counter = (uint8_t)instance->txPktCount++;

        int result = is_encode_binary_packet(toSend, dataSize, &hdr, 0, instance->buf.start, instance->buf.size);
        return result;
}

int is_comm_set_data(is_comm_instance_t* instance, uint32_t dataId, uint32_t offset, uint32_t size, void* data)
{
    return sendData(instance, dataId, offset, size, data, PID_SET_DATA);    
}    

int is_comm_data(is_comm_instance_t* instance, uint32_t dataId, uint32_t offset, uint32_t size, void* data)
{
    return sendData(instance, dataId, offset, size, data, PID_DATA);    
}    

int is_comm_stop_broadcasts_all_ports(is_comm_instance_t* instance)
{
    packet_hdr_t hdr;
    hdr.flags = 0;
    hdr.pid = PID_STOP_BROADCASTS_ALL_PORTS;
    hdr.counter = (uint8_t)instance->txPktCount++;

    return is_encode_binary_packet(0, 0, &hdr, 0, instance->buf.start, instance->buf.size);
}

int is_comm_stop_broadcasts_current_port(is_comm_instance_t* instance)
{
    packet_hdr_t hdr;
    hdr.flags = 0;
    hdr.pid = PID_STOP_BROADCASTS_CURRENT_PORT;
    hdr.counter = (uint8_t)instance->txPktCount++;

    return is_encode_binary_packet(0, 0, &hdr, 0, instance->buf.start, instance->buf.size);
}

#if 0

int is_comm_ack(is_comm_instance_t* instance, uint32_t did)
{
    if(did!=0 && instance->ackNeeded==0)
    {
        return 0;
    }
    
    int ackSize;
    bufPtr_t data;

    // Create and Send request packet
    p_ack_t ack;
    ack.hdr.pktInfo = instance->ackNeeded;
    ack.hdr.pktCounter = instance->pktCounter;
    ackSize = sizeof(p_ack_hdr_t);

    // Set ack body
    //     switch (pid)
    //     {
    //     case PID_SET_DATA:
    //         memcpy(&(ack.buf), (p_data_hdr_t*)(instance->buffer), sizeof(p_data_hdr_t));
    //         ackSize += sizeof(p_data_hdr_t);
    //         break;
    //     }

    data.ptr = (unsigned char*)&ack;
    data.size = ackSize;

    int result = is_encode_binary_packet(&ack, ackSize, &hdr, 0, instance->buffer, instance->bufferSize);

    instance->ackNeeded = 0;
}
#endif

void is_decode_binary_packet_footer(packet_ftr_t* ftr, uint8_t* ptrSrc, uint8_t** ptrSrcEnd, uint32_t* checksum)
{
        int state = 0;
        uint8_t* currentPtr = (*ptrSrcEnd) - 1;
        memset(ftr, 0, sizeof(uint32_t));

        // we need a state machine to ensure we don't overrun ptrSrcEnd
        while (state != 7 && currentPtr > ptrSrc)
        {
                switch (state)
                {
                case 0: // packet end byte
                        ftr->stopByte = *currentPtr--;
                        state = 1;
                        break;

                case 1: // packet checksum 1
                        ftr->cksum1 = *currentPtr--;
                        state = (3 - (*currentPtr == PSC_RESERVED_KEY));
                        break;

                case 2: // packet checksum 1 is encoded
                        ftr->cksum1 = ~ftr->cksum1;
                        currentPtr--;
                        state = 3;
                        break;

                case 3: // packet checksum 2
                        ftr->cksum2 = *currentPtr--;
                        state = (5 - (*currentPtr == PSC_RESERVED_KEY));
                        break;

                case 4: // packet checksum 2 is encoded
                        ftr->cksum2 = ~ftr->cksum2;
                        currentPtr--;
                        state = 5;
                        break;

                case 5: // packet checksum 3
                        ftr->cksum3 = *currentPtr;
                        state = (7 - (*(currentPtr - 1) == PSC_RESERVED_KEY));
                        break;

                case 6: // packet checksum 3 is encoded
                        ftr->cksum3 = ~ftr->cksum3;
                        currentPtr--;
                        state = 7;
                        break;

                default:
                        break;
                }
        }
        *ptrSrcEnd = currentPtr;
        *checksum = ((uint32_t)ftr->cksum1) | (0x0000FF00 & ((uint32_t)ftr->cksum2 << 8)) | (0x00FF0000 & ((uint32_t)ftr->cksum3 << 16));
}

int is_decode_binary_packet_byte(uint8_t** _ptrSrc, uint8_t** _ptrDest, uint32_t* checksum, uint32_t shift)
{
        uint8_t* ptrSrc = *_ptrSrc;

        // packet id byte
        uint32_t val = *ptrSrc++;
        switch (val)
        {
        case PSC_ASCII_START_BYTE:
        case PSC_ASCII_END_BYTE:
        case PSC_START_BYTE:
        case PSC_END_BYTE:
        case RTCM3_START_BYTE:
        case UBLOX_START_BYTE1:
                // corrupt data
                return -1;

        case PSC_RESERVED_KEY:
                // skip special byte
                val = (~(*ptrSrc++) & 0x000000FF);
                // fall through
        default:
                *checksum ^= (val << shift);
                *((*_ptrDest)++) = (uint8_t)val;
        }
        *_ptrSrc = ptrSrc;

        return 0;
}

int is_encode_binary_packet(void* srcBuffer, unsigned int srcBufferLength, packet_hdr_t* hdr, uint8_t additionalPktFlags, void* encodedPacket, int encodedPacketLength)
{
        // Ensure data size is small enough, assuming packet size could double after encoding.
        if (srcBufferLength > MAX_PKT_BODY_SIZE)
        {
                return -1;
        }

        // Update Packet Counter
        uint8_t* ptrSrc;
        uint8_t* ptrSrcEnd;
        uint8_t* ptrDest = (uint8_t*)encodedPacket;
        uint8_t* ptrDestEnd = ptrDest + encodedPacketLength;
        uint32_t shifter = 0;
        uint32_t checkSumValue = CHECKSUM_SEED;
        uint32_t val;

        if (ptrDest >= ptrDestEnd)
        {
                return -1;
        }
        // Packet header -------------------------------------------------------------------------------------------
        *ptrDest++ = PSC_START_BYTE;

        // PID
        if (ptrDest >= ptrDestEnd)
        {
                return -1;
        }
        val = hdr->pid;
        ptrDest = encodeByteAddToBuffer(val, ptrDest);
        checkSumValue ^= val;

        // Counter
        if (ptrDest >= ptrDestEnd)
        {
                return -1;
        }
        val = hdr->counter;
        ptrDest = encodeByteAddToBuffer(val, ptrDest);
        checkSumValue ^= (val << 8);

        // Flags
        if (ptrDest >= ptrDestEnd)
        {
                return -1;
        }
        val = hdr->flags | additionalPktFlags | CPU_IS_LITTLE_ENDIAN | CM_PKT_FLAGS_CHECKSUM_24_BIT;
        ptrDest = encodeByteAddToBuffer(val, ptrDest);
        checkSumValue ^= (val << 16);

        // Packet body ----------------------------------------------------------------------------------------------
        if (srcBufferLength > 0)
        {
                ptrSrc = (uint8_t*)srcBuffer;
                ptrSrcEnd = ptrSrc + srcBufferLength;

                // copy body bytes, doing encoding and checksum
                while (ptrSrc != ptrSrcEnd && ptrDest < ptrDestEnd)
                {
                        val = *ptrSrc++;
                        checkSumValue ^= (val << shifter);

                        // increment shifter
                        shifter += 8;

                        // reset if shifter equals 24
                        shifter *= (shifter != 24);

                        ptrDest = encodeByteAddToBuffer(val, ptrDest);
                }
        }

        // footer ----------------------------------------------------------------------------------------------------

        // checksum byte 3
        if (ptrDest >= ptrDestEnd)
        {
                return -1;
        }
        val = (uint8_t)((checkSumValue >> 16) & 0xFF);
        ptrDest = encodeByteAddToBuffer(val, ptrDest);

        // checksum byte 2
        if (ptrDest >= ptrDestEnd)
        {
                return -1;
        }
        val = (uint8_t)(checkSumValue >> 8) & 0xFF;
        ptrDest = encodeByteAddToBuffer(val, ptrDest);

        // checksum byte 1
        if (ptrDest >= ptrDestEnd)
        {
                return -1;
        }
        val = (uint8_t)(checkSumValue & 0xFF);
        ptrDest = encodeByteAddToBuffer(val, ptrDest);

        // packet end byte
        if (ptrDest >= ptrDestEnd)
        {
                return -1;
        }
        *ptrDest++ = PSC_END_BYTE;
    return (int)(ptrDest - (uint8_t*)encodedPacket);
}

// This function will decode a packet in place if altBuf is NULL.
int is_decode_binary_packet(packet_t* pkt, unsigned char* pbuf, int pbufSize)
{
        // before we even get in this method, we can be assured that pbuf starts with a packet start byte and ends with a packet end byte
        // all other data can potentially be garbage
        if (pbufSize < 8)
        {
                // corrupt data
                return -1;
        }

        // decode the body and calculate checksum
        uint8_t* ptrSrc = pbuf;
        uint8_t* ptrSrcEnd = pbuf + pbufSize;
        packet_ftr_t ftr;
        uint32_t actualCheckSumValue;

        is_decode_binary_packet_footer(&ftr, ptrSrc, &ptrSrcEnd, &actualCheckSumValue);
        uint32_t shifter = 0;
        uint32_t checkSumValue = CHECKSUM_SEED;

        // start packet byte
        uint8_t* ptrDest = (uint8_t*)&pkt->hdr;
        *ptrDest++ = *ptrSrc++;

        if
        (
                // packet id
                is_decode_binary_packet_byte(&ptrSrc, &ptrDest, &checkSumValue, 0) ||

                // packet counter
                is_decode_binary_packet_byte(&ptrSrc, &ptrDest, &checkSumValue, 8) ||

                // packet flags
                is_decode_binary_packet_byte(&ptrSrc, &ptrDest, &checkSumValue, 16)
        )
        {
                return -1;
        }

        // decode the body - start shift 0
        ptrDest = pkt->body.ptr;
        while (ptrSrc < ptrSrcEnd)
        {
                if (is_decode_binary_packet_byte(&ptrSrc, &ptrDest, &checkSumValue, shifter))
                {
                        return -1;
                }

                shifter += 8;

                // reset if shifter equals 24
                shifter *= (shifter != 24);
        }

        if (actualCheckSumValue != checkSumValue)
        {
                // corrupt data
                return -1;
        }

        pkt->body.size = (uint32_t)(ptrDest - pkt->body.ptr);
        if (pkt->body.size > MAX_PKT_BODY_SIZE)
        {
                return -1;
        }

        // if the endianness of the packet doesn't match our CPU, we need to flip the data so it will be correct for our CPU architecture
        else if (pkt->body.size != 0 && (pkt->hdr.flags & CM_PKT_FLAGS_ENDIANNESS_MASK) != CPU_IS_LITTLE_ENDIAN)
        {
                swapPacket(pkt);
        }

        return 0;
}

char copyDataPToStructP(void *sptr, const p_data_t *data, const unsigned int maxsize)
{
    if ((data->hdr.size + data->hdr.offset) <= maxsize)
    {
        memcpy((uint8_t*)sptr + data->hdr.offset, data->buf, data->hdr.size);
        return 0;
    }
    else
    {
        return -1;
    }
}

char copyDataPToStructP2(void *sptr, const p_data_hdr_t *dataHdr, const uint8_t *dataBuf, const unsigned int maxsize)
{
    if ((dataHdr->size + dataHdr->offset) <= maxsize)
    {
        memcpy((uint8_t*)sptr + dataHdr->offset, dataBuf, dataHdr->size);
        return 0;
    }
    else
    {
        return -1;
    }
}

void is_enable_packet_encoding(int enabled)
{
        s_packetEncodingEnabled = enabled;
}

char is_comm_copy_to_struct(void *sptr, const is_comm_instance_t *instance, const unsigned int maxsize)
{    
    if ((instance->dataHdr.size + instance->dataHdr.offset) <= maxsize)
    {
        memcpy((uint8_t*)sptr + instance->dataHdr.offset, instance->dataPtr, instance->dataHdr.size);
        return 0;
    }
    else
    {
        return -1;
    }
}