gex-client-c/gex/protocol/TinyFrame.c

//---------------------------------------------------------------------------
#include "TinyFrame.h"
#include <malloc.h>
//---------------------------------------------------------------------------

// Compatibility with ESP8266 SDK
#ifdef ICACHE_FLASH_ATTR
#define _TF_FN ICACHE_FLASH_ATTR
#else
#define _TF_FN
#endif

// Helper macros
#define TF_MAX(a, b) ((a)>(b)?(a):(b))
#define TF_MIN(a, b) ((a)<(b)?(a):(b))

// TODO It would be nice to have per-instance configurable checksum types, but that would
// mandate configurable field sizes unless we use u32 everywhere (and possibly shorten
// it when encoding to the buffer). I don't really like this idea so much. -MP

//region Checksums

#if TF_CKSUM_TYPE == TF_CKSUM_NONE

// NONE
#define CKSUM_RESET(cksum)
#define CKSUM_ADD(cksum, byte)
#define CKSUM_FINALIZE(cksum)

#elif TF_CKSUM_TYPE == TF_CKSUM_XOR

// ~XOR
#define CKSUM_RESET(cksum) do { (cksum) = 0; } while (0)
#define CKSUM_ADD(cksum, byte) do { (cksum) ^= (byte); } while(0)
#define CKSUM_FINALIZE(cksum)  do { (cksum) = (TF_CKSUM)~cksum; } while(0)

#elif TF_CKSUM_TYPE == TF_CKSUM_CRC16

// TODO try to replace with an algorithm
/** CRC table for the CRC-16. The poly is 0x8005 (x^16 + x^15 + x^2 + 1) */
static const uint16_t crc16_table[256] = {
    0x0000, 0xC0C1, 0xC181, 0x0140, 0xC301, 0x03C0, 0x0280, 0xC241,
    0xC601, 0x06C0, 0x0780, 0xC741, 0x0500, 0xC5C1, 0xC481, 0x0440,
    0xCC01, 0x0CC0, 0x0D80, 0xCD41, 0x0F00, 0xCFC1, 0xCE81, 0x0E40,
    0x0A00, 0xCAC1, 0xCB81, 0x0B40, 0xC901, 0x09C0, 0x0880, 0xC841,
    0xD801, 0x18C0, 0x1980, 0xD941, 0x1B00, 0xDBC1, 0xDA81, 0x1A40,
    0x1E00, 0xDEC1, 0xDF81, 0x1F40, 0xDD01, 0x1DC0, 0x1C80, 0xDC41,
    0x1400, 0xD4C1, 0xD581, 0x1540, 0xD701, 0x17C0, 0x1680, 0xD641,
    0xD201, 0x12C0, 0x1380, 0xD341, 0x1100, 0xD1C1, 0xD081, 0x1040,
    0xF001, 0x30C0, 0x3180, 0xF141, 0x3300, 0xF3C1, 0xF281, 0x3240,
    0x3600, 0xF6C1, 0xF781, 0x3740, 0xF501, 0x35C0, 0x3480, 0xF441,
    0x3C00, 0xFCC1, 0xFD81, 0x3D40, 0xFF01, 0x3FC0, 0x3E80, 0xFE41,
    0xFA01, 0x3AC0, 0x3B80, 0xFB41, 0x3900, 0xF9C1, 0xF881, 0x3840,
    0x2800, 0xE8C1, 0xE981, 0x2940, 0xEB01, 0x2BC0, 0x2A80, 0xEA41,
    0xEE01, 0x2EC0, 0x2F80, 0xEF41, 0x2D00, 0xEDC1, 0xEC81, 0x2C40,
    0xE401, 0x24C0, 0x2580, 0xE541, 0x2700, 0xE7C1, 0xE681, 0x2640,
    0x2200, 0xE2C1, 0xE381, 0x2340, 0xE101, 0x21C0, 0x2080, 0xE041,
    0xA001, 0x60C0, 0x6180, 0xA141, 0x6300, 0xA3C1, 0xA281, 0x6240,
    0x6600, 0xA6C1, 0xA781, 0x6740, 0xA501, 0x65C0, 0x6480, 0xA441,
    0x6C00, 0xACC1, 0xAD81, 0x6D40, 0xAF01, 0x6FC0, 0x6E80, 0xAE41,
    0xAA01, 0x6AC0, 0x6B80, 0xAB41, 0x6900, 0xA9C1, 0xA881, 0x6840,
    0x7800, 0xB8C1, 0xB981, 0x7940, 0xBB01, 0x7BC0, 0x7A80, 0xBA41,
    0xBE01, 0x7EC0, 0x7F80, 0xBF41, 0x7D00, 0xBDC1, 0xBC81, 0x7C40,
    0xB401, 0x74C0, 0x7580, 0xB541, 0x7700, 0xB7C1, 0xB681, 0x7640,
    0x7200, 0xB2C1, 0xB381, 0x7340, 0xB101, 0x71C0, 0x7080, 0xB041,
    0x5000, 0x90C1, 0x9181, 0x5140, 0x9301, 0x53C0, 0x5280, 0x9241,
    0x9601, 0x56C0, 0x5780, 0x9741, 0x5500, 0x95C1, 0x9481, 0x5440,
    0x9C01, 0x5CC0, 0x5D80, 0x9D41, 0x5F00, 0x9FC1, 0x9E81, 0x5E40,
    0x5A00, 0x9AC1, 0x9B81, 0x5B40, 0x9901, 0x59C0, 0x5880, 0x9841,
    0x8801, 0x48C0, 0x4980, 0x8941, 0x4B00, 0x8BC1, 0x8A81, 0x4A40,
    0x4E00, 0x8EC1, 0x8F81, 0x4F40, 0x8D01, 0x4DC0, 0x4C80, 0x8C41,
    0x4400, 0x84C1, 0x8581, 0x4540, 0x8701, 0x47C0, 0x4680, 0x8641,
    0x8201, 0x42C0, 0x4380, 0x8341, 0x4100, 0x81C1, 0x8081, 0x4040
};

static inline uint16_t crc16_byte(uint16_t cksum, const uint8_t byte)
{
    return (cksum >> 8) ^ crc16_table[(cksum ^ byte) & 0xff];
}

#define CKSUM_RESET(cksum) do { (cksum) = 0; } while (0)
#define CKSUM_ADD(cksum, byte) do { (cksum) = crc16_byte((cksum), (byte)); } while(0)
#define CKSUM_FINALIZE(cksum)

#elif TF_CKSUM_TYPE == TF_CKSUM_CRC32

// TODO try to replace with an algorithm
static const uint32_t crc32_table[] = { /* CRC polynomial 0xedb88320 */
    0x00000000, 0x77073096, 0xee0e612c, 0x990951ba, 0x076dc419, 0x706af48f,
    0xe963a535, 0x9e6495a3, 0x0edb8832, 0x79dcb8a4, 0xe0d5e91e, 0x97d2d988,
    0x09b64c2b, 0x7eb17cbd, 0xe7b82d07, 0x90bf1d91, 0x1db71064, 0x6ab020f2,
    0xf3b97148, 0x84be41de, 0x1adad47d, 0x6ddde4eb, 0xf4d4b551, 0x83d385c7,
    0x136c9856, 0x646ba8c0, 0xfd62f97a, 0x8a65c9ec, 0x14015c4f, 0x63066cd9,
    0xfa0f3d63, 0x8d080df5, 0x3b6e20c8, 0x4c69105e, 0xd56041e4, 0xa2677172,
    0x3c03e4d1, 0x4b04d447, 0xd20d85fd, 0xa50ab56b, 0x35b5a8fa, 0x42b2986c,
    0xdbbbc9d6, 0xacbcf940, 0x32d86ce3, 0x45df5c75, 0xdcd60dcf, 0xabd13d59,
    0x26d930ac, 0x51de003a, 0xc8d75180, 0xbfd06116, 0x21b4f4b5, 0x56b3c423,
    0xcfba9599, 0xb8bda50f, 0x2802b89e, 0x5f058808, 0xc60cd9b2, 0xb10be924,
    0x2f6f7c87, 0x58684c11, 0xc1611dab, 0xb6662d3d, 0x76dc4190, 0x01db7106,
    0x98d220bc, 0xefd5102a, 0x71b18589, 0x06b6b51f, 0x9fbfe4a5, 0xe8b8d433,
    0x7807c9a2, 0x0f00f934, 0x9609a88e, 0xe10e9818, 0x7f6a0dbb, 0x086d3d2d,
    0x91646c97, 0xe6635c01, 0x6b6b51f4, 0x1c6c6162, 0x856530d8, 0xf262004e,
    0x6c0695ed, 0x1b01a57b, 0x8208f4c1, 0xf50fc457, 0x65b0d9c6, 0x12b7e950,
    0x8bbeb8ea, 0xfcb9887c, 0x62dd1ddf, 0x15da2d49, 0x8cd37cf3, 0xfbd44c65,
    0x4db26158, 0x3ab551ce, 0xa3bc0074, 0xd4bb30e2, 0x4adfa541, 0x3dd895d7,
    0xa4d1c46d, 0xd3d6f4fb, 0x4369e96a, 0x346ed9fc, 0xad678846, 0xda60b8d0,
    0x44042d73, 0x33031de5, 0xaa0a4c5f, 0xdd0d7cc9, 0x5005713c, 0x270241aa,
    0xbe0b1010, 0xc90c2086, 0x5768b525, 0x206f85b3, 0xb966d409, 0xce61e49f,
    0x5edef90e, 0x29d9c998, 0xb0d09822, 0xc7d7a8b4, 0x59b33d17, 0x2eb40d81,
    0xb7bd5c3b, 0xc0ba6cad, 0xedb88320, 0x9abfb3b6, 0x03b6e20c, 0x74b1d29a,
    0xead54739, 0x9dd277af, 0x04db2615, 0x73dc1683, 0xe3630b12, 0x94643b84,
    0x0d6d6a3e, 0x7a6a5aa8, 0xe40ecf0b, 0x9309ff9d, 0x0a00ae27, 0x7d079eb1,
    0xf00f9344, 0x8708a3d2, 0x1e01f268, 0x6906c2fe, 0xf762575d, 0x806567cb,
    0x196c3671, 0x6e6b06e7, 0xfed41b76, 0x89d32be0, 0x10da7a5a, 0x67dd4acc,
    0xf9b9df6f, 0x8ebeeff9, 0x17b7be43, 0x60b08ed5, 0xd6d6a3e8, 0xa1d1937e,
    0x38d8c2c4, 0x4fdff252, 0xd1bb67f1, 0xa6bc5767, 0x3fb506dd, 0x48b2364b,
    0xd80d2bda, 0xaf0a1b4c, 0x36034af6, 0x41047a60, 0xdf60efc3, 0xa867df55,
    0x316e8eef, 0x4669be79, 0xcb61b38c, 0xbc66831a, 0x256fd2a0, 0x5268e236,
    0xcc0c7795, 0xbb0b4703, 0x220216b9, 0x5505262f, 0xc5ba3bbe, 0xb2bd0b28,
    0x2bb45a92, 0x5cb36a04, 0xc2d7ffa7, 0xb5d0cf31, 0x2cd99e8b, 0x5bdeae1d,
    0x9b64c2b0, 0xec63f226, 0x756aa39c, 0x026d930a, 0x9c0906a9, 0xeb0e363f,
    0x72076785, 0x05005713, 0x95bf4a82, 0xe2b87a14, 0x7bb12bae, 0x0cb61b38,
    0x92d28e9b, 0xe5d5be0d, 0x7cdcefb7, 0x0bdbdf21, 0x86d3d2d4, 0xf1d4e242,
    0x68ddb3f8, 0x1fda836e, 0x81be16cd, 0xf6b9265b, 0x6fb077e1, 0x18b74777,
    0x88085ae6, 0xff0f6a70, 0x66063bca, 0x11010b5c, 0x8f659eff, 0xf862ae69,
    0x616bffd3, 0x166ccf45, 0xa00ae278, 0xd70dd2ee, 0x4e048354, 0x3903b3c2,
    0xa7672661, 0xd06016f7, 0x4969474d, 0x3e6e77db, 0xaed16a4a, 0xd9d65adc,
    0x40df0b66, 0x37d83bf0, 0xa9bcae53, 0xdebb9ec5, 0x47b2cf7f, 0x30b5ffe9,
    0xbdbdf21c, 0xcabac28a, 0x53b39330, 0x24b4a3a6, 0xbad03605, 0xcdd70693,
    0x54de5729, 0x23d967bf, 0xb3667a2e, 0xc4614ab8, 0x5d681b02, 0x2a6f2b94,
    0xb40bbe37, 0xc30c8ea1, 0x5a05df1b, 0x2d02ef8d
};

static inline uint32_t crc32_byte(uint32_t cksum, const uint8_t byte)
{
    return (crc32_table[((cksum) ^ ((uint8_t)byte)) & 0xff] ^ ((cksum) >> 8));
}

#define CKSUM_RESET(cksum) do { (cksum) = (TF_CKSUM)0xFFFFFFFF; } while (0)
#define CKSUM_ADD(cksum, byte) do { (cksum) = crc32_byte(cksum, byte); } while(0)
#define CKSUM_FINALIZE(cksum)  do { (cksum) = (TF_CKSUM)~(cksum); } while(0)

#endif

//endregion

/** Init with a user-allocated buffer */
void _TF_FN TF_InitStatic(TinyFrame *tf, TF_Peer peer_bit)
{
    if (tf == NULL) return;

    // Zero it out, keeping user config
    uint32_t usertag = tf->usertag;
    void * userdata = tf->userdata;

    memset(tf, 0, sizeof(struct TinyFrame_));

    tf->usertag = usertag;
    tf->userdata = userdata;

    tf->peer_bit = peer_bit;
}

/** Init with malloc */
TinyFrame * _TF_FN TF_Init(TF_Peer peer_bit)
{
    TinyFrame *tf = malloc(sizeof(TinyFrame));
    TF_InitStatic(tf, peer_bit);
    return tf;
}

//region Listeners

/** Reset ID listener's timeout to the original value */
static inline void _TF_FN renew_id_listener(struct TF_IdListener_ *lst)
{
    lst->timeout = lst->timeout_max;
}

/** Notify callback about ID listener's demise & let it free any resources in userdata */
static void _TF_FN cleanup_id_listener(TinyFrame *tf, TF_COUNT i, struct TF_IdListener_ *lst)
{
    TF_Msg msg;
    if (lst->fn == NULL) return;

    // Make user clean up their data - only if not NULL
    if (lst->userdata != NULL) {
        msg.userdata = lst->userdata;
        msg.userdata2 = lst->userdata2;
        msg.data = NULL; // this is a signal that the listener should clean up
        lst->fn(tf, &msg); // return value is ignored here - use TF_STAY or TF_CLOSE
    }

    lst->fn = NULL; // Discard listener

    if (i == tf->count_id_lst - 1) {
        tf->count_id_lst--;
    }
}

/** Clean up Type listener */
static inline void _TF_FN cleanup_type_listener(TinyFrame *tf, TF_COUNT i, struct TF_TypeListener_ *lst)
{
    lst->fn = NULL; // Discard listener
    if (i == tf->count_type_lst - 1) {
        tf->count_type_lst--;
    }
}

/** Clean up Generic listener */
static inline void _TF_FN cleanup_generic_listener(TinyFrame *tf, TF_COUNT i, struct TF_GenericListener_ *lst)
{
    lst->fn = NULL; // Discard listener
    if (i == tf->count_generic_lst - 1) {
        tf->count_generic_lst--;
    }
}

/** Add a new ID listener. Returns 1 on success. */
bool _TF_FN TF_AddIdListener(TinyFrame *tf, TF_Msg *msg, TF_Listener cb, TF_TICKS timeout)
{
    TF_COUNT i;
    struct TF_IdListener_ *lst;
    for (i = 0; i < TF_MAX_ID_LST; i++) {
        lst = &tf->id_listeners[i];
        // test for empty slot
        if (lst->fn == NULL) {
            lst->fn = cb;
            lst->id = msg->frame_id;
            lst->userdata = msg->userdata;
            lst->userdata2 = msg->userdata2;
            lst->timeout_max = lst->timeout = timeout;
            if (i >= tf->count_id_lst) {
                tf->count_id_lst = (TF_COUNT) (i + 1);
            }
            return true;
        }
    }
    return false;
}

/** Add a new Type listener. Returns 1 on success. */
bool _TF_FN TF_AddTypeListener(TinyFrame *tf, TF_TYPE frame_type, TF_Listener cb)
{
    TF_COUNT i;
    struct TF_TypeListener_ *lst;
    for (i = 0; i < TF_MAX_TYPE_LST; i++) {
        lst = &tf->type_listeners[i];
        // test for empty slot
        if (lst->fn == NULL) {
            lst->fn = cb;
            lst->type = frame_type;
            if (i >= tf->count_type_lst) {
                tf->count_type_lst = (TF_COUNT) (i + 1);
            }
            return true;
        }
    }
    return false;
}

/** Add a new Generic listener. Returns 1 on success. */
bool _TF_FN TF_AddGenericListener(TinyFrame *tf, TF_Listener cb)
{
    TF_COUNT i;
    struct TF_GenericListener_ *lst;
    for (i = 0; i < TF_MAX_GEN_LST; i++) {
        lst = &tf->generic_listeners[i];
        // test for empty slot
        if (lst->fn == NULL) {
            lst->fn = cb;
            if (i >= tf->count_generic_lst) {
                tf->count_generic_lst = (TF_COUNT) (i + 1);
            }
            return true;
        }
    }
    return false;
}

/** Remove a ID listener by its frame ID. Returns 1 on success. */
bool _TF_FN TF_RemoveIdListener(TinyFrame *tf, TF_ID frame_id)
{
    TF_COUNT i;
    struct TF_IdListener_ *lst;
    for (i = 0; i < tf->count_id_lst; i++) {
        lst = &tf->id_listeners[i];
        // test if live & matching
        if (lst->fn != NULL && lst->id == frame_id) {
            cleanup_id_listener(tf, i, lst);
            return true;
        }
    }
    return false;
}

/** Remove a type listener by its type. Returns 1 on success. */
bool _TF_FN TF_RemoveTypeListener(TinyFrame *tf, TF_TYPE type)
{
    TF_COUNT i;
    struct TF_TypeListener_ *lst;
    for (i = 0; i < tf->count_type_lst; i++) {
        lst = &tf->type_listeners[i];
        // test if live & matching
        if (lst->fn != NULL    && lst->type == type) {
            cleanup_type_listener(tf, i, lst);
            return true;
        }
    }
    return false;
}

/** Remove a generic listener by its function pointer. Returns 1 on success. */
bool _TF_FN TF_RemoveGenericListener(TinyFrame *tf, TF_Listener cb)
{
    TF_COUNT i;
    struct TF_GenericListener_ *lst;
    for (i = 0; i < tf->count_generic_lst; i++) {
        lst = &tf->generic_listeners[i];
        // test if live & matching
        if (lst->fn == cb) {
            cleanup_generic_listener(tf, i, lst);
            return true;
        }
    }
    return false;
}

/** Handle a message that was just collected & verified by the parser */
static void _TF_FN TF_HandleReceivedMessage(TinyFrame *tf)
{
    TF_COUNT i;
    struct TF_IdListener_ *ilst;
    struct TF_TypeListener_ *tlst;
    struct TF_GenericListener_ *glst;
    TF_Result res;

    // Prepare message object
    TF_Msg msg;
    TF_ClearMsg(&msg);
    msg.frame_id = tf->id;
    msg.is_response = false;
    msg.type = tf->type;
    msg.data = tf->data;
    msg.len = tf->len;

    // Any listener can consume the message, or let someone else handle it.

    // The loop upper bounds are the highest currently used slot index
    // (or close to it, depending on the order of listener removals).

    // ID listeners first
    for (i = 0; i < tf->count_id_lst; i++) {
        ilst = &tf->id_listeners[i];

        if (ilst->fn && ilst->id == msg.frame_id) {
            msg.userdata = ilst->userdata; // pass userdata pointer to the callback
            msg.userdata2 = ilst->userdata2;
            res = ilst->fn(tf, &msg);
            ilst->userdata = msg.userdata; // put it back (may have changed the pointer or set to NULL)
            ilst->userdata2 = msg.userdata2; // put it back (may have changed the pointer or set to NULL)

            if (res != TF_NEXT) {
                // if it's TF_CLOSE, we assume user already cleaned up userdata
                if (res == TF_RENEW) {
                    renew_id_listener(ilst);
                }
                return;
            }
        }
    }
    // clean up for the following listeners that don't use userdata (this avoids data from
    // an ID listener that returned TF_NEXT from leaking into Type and Generic listeners)
    msg.userdata = NULL;
    msg.userdata2 = NULL;

    // Type listeners
    for (i = 0; i < tf->count_type_lst; i++) {
        tlst = &tf->type_listeners[i];

        if (tlst->fn && tlst->type == msg.type) {
            res = tlst->fn(tf, &msg);

            if (res != TF_NEXT) {
                // if it's TF_CLOSE, we assume user already cleaned up userdata
                // TF_RENEW doesn't make sense here because type listeners don't expire
                return;
            }
        }
    }

    // Generic listeners
    for (i = 0; i < tf->count_generic_lst; i++) {
        glst = &tf->generic_listeners[i];

        if (glst->fn) {
            res = glst->fn(tf, &msg);

            if (res != TF_NEXT) {
                // if it's TF_CLOSE, we assume user already cleaned up userdata
                // TF_RENEW doesn't make sense here because generic listeners don't expire
                return;
            }
        }
    }
}

//endregion Listeners

/** Handle a received byte buffer */
void _TF_FN TF_Accept(TinyFrame *tf, const uint8_t *buffer, size_t count)
{
    size_t i;
    for (i = 0; i < count; i++) {
        TF_AcceptChar(tf, buffer[i]);
    }
}

/** Reset the parser's internal state. */
void _TF_FN TF_ResetParser(TinyFrame *tf)
{
    tf->state = TFState_SOF;
    // more init will be done by the parser when the first byte is received
}

/** SOF was received - prepare for the frame */
static void _TF_FN pars_begin_frame(TinyFrame *tf) {
    // Reset state vars
    CKSUM_RESET(tf->cksum);
#if TF_USE_SOF_BYTE
    CKSUM_ADD(tf->cksum, TF_SOF_BYTE);
#endif

    tf->discard_data = false;

    // Enter ID state
    tf->state = TFState_ID;
    tf->rxi = 0;
}

/** Handle a received char - here's the main state machine */
void _TF_FN TF_AcceptChar(TinyFrame *tf, unsigned char c)
{
    // Parser timeout - clear
    if (tf->parser_timeout_ticks >= TF_PARSER_TIMEOUT_TICKS) {
        TF_ResetParser(tf);
    }
    tf->parser_timeout_ticks = 0;

// DRY snippet - collect multi-byte number from the input stream, byte by byte
// This is a little dirty, but makes the code easier to read. It's used like e.g. if(),
// the body is run only after the entire number (of data type 'type') was received
// and stored to 'dest'
#define COLLECT_NUMBER(dest, type) dest = (type)(((dest) << 8) | c); \
                                   if (++tf->rxi == sizeof(type))

#if !TF_USE_SOF_BYTE
    if (tf->state == TFState_SOF) {
            TF_ParsBeginFrame();
        }
#endif

    switch (tf->state) {
        case TFState_SOF:
            if (c == TF_SOF_BYTE) {
                pars_begin_frame(tf);
            }
            break;

        case TFState_ID:
            CKSUM_ADD(tf->cksum, c);
            COLLECT_NUMBER(tf->id, TF_ID) {
                // Enter LEN state
                tf->state = TFState_LEN;
                tf->rxi = 0;
            }
            break;

        case TFState_LEN:
            CKSUM_ADD(tf->cksum, c);
            COLLECT_NUMBER(tf->len, TF_LEN) {
                // Enter TYPE state
                tf->state = TFState_TYPE;
                tf->rxi = 0;
            }
            break;

        case TFState_TYPE:
            CKSUM_ADD(tf->cksum, c);
            COLLECT_NUMBER(tf->type, TF_TYPE) {
#if TF_CKSUM_TYPE == TF_CKSUM_NONE
                tf->state = TFState_DATA;
                tf->rxi = 0;
#else
                // enter HEAD_CKSUM state
                tf->state = TFState_HEAD_CKSUM;
                tf->rxi = 0;
                tf->ref_cksum = 0;
#endif
            }
            break;

        case TFState_HEAD_CKSUM:
            COLLECT_NUMBER(tf->ref_cksum, TF_CKSUM) {
                // Check the header checksum against the computed value
                CKSUM_FINALIZE(tf->cksum);

                if (tf->cksum != tf->ref_cksum) {
                    TF_ResetParser(tf);
                    break;
                }

                if (tf->len == 0) {
                    TF_HandleReceivedMessage(tf);
                    TF_ResetParser(tf);
                    break;
                }

                // Enter DATA state
                tf->state = TFState_DATA;
                tf->rxi = 0;

                CKSUM_RESET(tf->cksum); // Start collecting the payload

                if (tf->len >= TF_MAX_PAYLOAD_RX) {
                    // ERROR - frame too long. Consume, but do not store.
                    tf->discard_data = true;
                }
            }
            break;

        case TFState_DATA:
            if (tf->discard_data) {
                tf->rxi++;
            } else {
                CKSUM_ADD(tf->cksum, c);
                tf->data[tf->rxi++] = c;
            }

            if (tf->rxi == tf->len) {
#if TF_CKSUM_TYPE == TF_CKSUM_NONE
                // All done
                TF_HandleReceivedMessage();
                TF_ResetParser();
#else
                // Enter DATA_CKSUM state
                tf->state = TFState_DATA_CKSUM;
                tf->rxi = 0;
                tf->ref_cksum = 0;
#endif
            }
            break;

        case TFState_DATA_CKSUM:
            COLLECT_NUMBER(tf->ref_cksum, TF_CKSUM) {
                // Check the header checksum against the computed value
                CKSUM_FINALIZE(tf->cksum);
                if (!tf->discard_data && tf->cksum == tf->ref_cksum) {
                    TF_HandleReceivedMessage(tf);
                }

                TF_ResetParser(tf);
            }
            break;
    }

    // we get here after finishing HEAD, if no data are to be received - handle and clear
    if (tf->len == 0 && tf->state == TFState_DATA) {
        TF_HandleReceivedMessage(tf);
        TF_ResetParser(tf);
    }
}

// Helper macros for the Compose functions
// use variables: si - signed int, b - byte, outbuff - target buffer, pos - count of bytes in buffer

/**
 * Write a number to the output buffer.
 *
 * @param type - data type
 * @param num - number to write
 * @param xtra - extra callback run after each byte, 'b' now contains the byte.
 */
#define WRITENUM_BASE(type, num, xtra) \
    for (si = sizeof(type)-1; si>=0; si--) { \
        b = (uint8_t)((num) >> (si*8) & 0xFF); \
        outbuff[pos++] = b; \
        xtra; \
    }

/**
 * Do nothing
 */
#define _NOOP()

/**
 * Write a number without adding its bytes to the checksum
 *
 * @param type - data type
 * @param num - number to write
 */
#define WRITENUM(type, num)       WRITENUM_BASE(type, num, _NOOP())

/**
 * Write a number AND add its bytes to the checksum
 *
 * @param type - data type
 * @param num - number to write
 */
#define WRITENUM_CKSUM(type, num) WRITENUM_BASE(type, num, CKSUM_ADD(cksum, b))

/**
 * Compose a frame (used internally by TF_Send and TF_Respond).
 * The frame can be sent using TF_WriteImpl(), or received by TF_Accept()
 *
 * @param outbuff - buffer to store the result in
 * @param msg - message written to the buffer
 * @return nr of bytes in outbuff used by the frame, 0 on failure
 */
static inline size_t _TF_FN TF_ComposeHead(TinyFrame *tf, uint8_t *outbuff, TF_Msg *msg)
{
    int8_t si = 0; // signed small int
    uint8_t b = 0;
    TF_ID id = 0;
    TF_CKSUM cksum = 0;
    size_t pos = 0; // can be needed to grow larger than TF_LEN

    (void)cksum;

    CKSUM_RESET(cksum);

    // Gen ID
    if (msg->is_response) {
        id = msg->frame_id;
    }
    else {
        id = (TF_ID) (tf->next_id++ & TF_ID_MASK);
        if (tf->peer_bit) {
            id |= TF_ID_PEERBIT;
        }
    }

    msg->frame_id = id; // put the resolved ID into the message object for later use

    // --- Start ---
    CKSUM_RESET(cksum);

#if TF_USE_SOF_BYTE
    outbuff[pos++] = TF_SOF_BYTE;
    CKSUM_ADD(cksum, TF_SOF_BYTE);
#endif

    WRITENUM_CKSUM(TF_ID, id);
    WRITENUM_CKSUM(TF_LEN, msg->len);
    WRITENUM_CKSUM(TF_TYPE, msg->type);

#if TF_CKSUM_TYPE != TF_CKSUM_NONE
    CKSUM_FINALIZE(cksum);
    WRITENUM(TF_CKSUM, cksum);
#endif

    return pos;
}

/**
 * Compose a frame (used internally by TF_Send and TF_Respond).
 * The frame can be sent using TF_WriteImpl(), or received by TF_Accept()
 *
 * @param outbuff - buffer to store the result in
 * @param data - data buffer
 * @param data_len - data buffer len
 * @param cksum - checksum variable, used for all calls to TF_ComposeBody. Must be reset before first use! (CKSUM_RESET(cksum);)
 * @return nr of bytes in outbuff used
 */
static size_t _TF_FN TF_ComposeBody(uint8_t *outbuff,
                                    const uint8_t *data, TF_LEN data_len,
                                    TF_CKSUM *cksum)
{
    TF_LEN i = 0;
    uint8_t b = 0;
    size_t pos = 0;

    for (i = 0; i < data_len; i++) {
        b = data[i];
        outbuff[pos++] = b;
        CKSUM_ADD(*cksum, b);
    }

    return pos;
}

/**
 * Finalize a frame
 *
 * @param outbuff - buffer to store the result in
 * @param cksum - checksum variable used for the body
 * @return nr of bytes in outbuff used
 */
static size_t _TF_FN TF_ComposeTail(uint8_t *outbuff, const TF_CKSUM *cksum)
{
    int8_t si = 0; // signed small int
    uint8_t b = 0;
    size_t pos = 0;

#if TF_CKSUM_TYPE != TF_CKSUM_NONE
    CKSUM_FINALIZE(*cksum);
    WRITENUM(TF_CKSUM, *cksum);
#endif
    return pos;
}

/**
 * Send a message
 *
 * @param tf - instance
 * @param msg - message object
 * @param listener - ID listener, or NULL
 * @param timeout - listener timeout, 0 is none
 * @return true if sent
 */
static bool _TF_FN TF_SendFrame(TinyFrame *tf, TF_Msg *msg, TF_Listener listener, TF_TICKS timeout)
{
    size_t len = 0;
    size_t remain = 0;
    size_t sent = 0;
    TF_CKSUM cksum = 0;

    TF_ClaimTx(tf);

    len = TF_ComposeHead(tf, tf->sendbuf, msg);
    if (listener) TF_AddIdListener(tf, msg, listener, timeout);

    CKSUM_RESET(cksum);

    remain = msg->len;
    while (remain > 0) {
        size_t chunk = TF_MIN(TF_SENDBUF_LEN - len, remain);
        len += TF_ComposeBody(tf->sendbuf+len, msg->data+sent, (TF_LEN) chunk, &cksum);
        remain -= chunk;
        sent += chunk;

        // Flush if the buffer is full and we have more to send
        if (remain > 0 && len == TF_SENDBUF_LEN) {
            TF_WriteImpl(tf, (const uint8_t *) tf->sendbuf, len);
            len = 0;
        }
    }

    // Flush if checksum wouldn't fit in the buffer
    if (TF_SENDBUF_LEN - len < sizeof(TF_CKSUM)) {
        TF_WriteImpl(tf, (const uint8_t *) tf->sendbuf, len);
        len = 0;
    }

    // Add checksum, flush what remains to be sent
    len += TF_ComposeTail(tf->sendbuf+len, &cksum);
    TF_WriteImpl(tf, (const uint8_t *) tf->sendbuf, len);

    TF_ReleaseTx(tf);

    return true;
}

/** send without listener */
bool _TF_FN TF_Send(TinyFrame *tf, TF_Msg *msg)
{
    return TF_SendFrame(tf, msg, NULL, 0);
}

/** send without listener and struct */
bool _TF_FN TF_SendSimple(TinyFrame *tf, TF_TYPE type, const uint8_t *data, TF_LEN len)
{
    TF_Msg msg;
    TF_ClearMsg(&msg);
    msg.type = type;
    msg.data = data;
    msg.len = len;
    return TF_Send(tf, &msg);
}

/** send with a listener waiting for a reply, without the struct */
bool _TF_FN TF_QuerySimple(TinyFrame *tf, TF_TYPE type, const uint8_t *data, TF_LEN len, TF_Listener listener, TF_TICKS timeout)
{
    TF_Msg msg;
    TF_ClearMsg(&msg);
    msg.type = type;
    msg.data = data;
    msg.len = len;
    return TF_SendFrame(tf, &msg, listener, timeout);
}

/** send with a listener waiting for a reply */
bool _TF_FN TF_Query(TinyFrame *tf, TF_Msg *msg, TF_Listener listener, TF_TICKS timeout)
{
    return TF_SendFrame(tf, msg, listener, timeout);
}

/** Like TF_Send, but with explicit frame ID (set inside the msg object), use for responses */
bool _TF_FN TF_Respond(TinyFrame *tf, TF_Msg *msg)
{
    msg->is_response = true;
    return TF_Send(tf, msg);
}

/** Externally renew an ID listener */
bool _TF_FN TF_RenewIdListener(TinyFrame *tf, TF_ID id)
{
    TF_COUNT i;
    struct TF_IdListener_ *lst;
    for (i = 0; i < tf->count_id_lst; i++) {
        lst = &tf->id_listeners[i];
        // test if live & matching
        if (lst->fn != NULL && lst->id == id) {
            renew_id_listener(lst);
            return true;
        }
    }
    return false;
}

/** Timebase hook - for timeouts */
void _TF_FN TF_Tick(TinyFrame *tf)
{
    TF_COUNT i = 0;
    struct TF_IdListener_ *lst;

    // increment parser timeout (timeout is handled when receiving next byte)
    if (tf->parser_timeout_ticks < TF_PARSER_TIMEOUT_TICKS) {
        tf->parser_timeout_ticks++;
    }

    // decrement and expire ID listeners
    for (i = 0; i < tf->count_id_lst; i++) {
        lst = &tf->id_listeners[i];
        if (!lst->fn || lst->timeout == 0) continue;
        // count down...
        if (--lst->timeout == 0) {
            // Listener has expired
            cleanup_id_listener(tf, i, lst);
        }
    }
}

/** Default impl for claiming write mutex; can be specific to the instance */
void __attribute__((weak)) TF_ClaimTx(TinyFrame *tf)
{
    (void) tf;

    // do nothing
}

/** Default impl for releasing write mutex; can be specific to the instance */
void __attribute__((weak)) TF_ReleaseTx(TinyFrame *tf)
{
    (void) tf;

    // do nothing
}