struct fota_seg_hdr {
    uint32_t crc;
    uint32_t size;
    uint32_t upi_ver;                   // seems to be 0x00014050
    uint32_t scout_ver;                 // seems to be 0x00013880
    uint32_t flags1;
    uint32_t flags2;
    uint32_t field_18;
    uint32_t field_1c;
    uint32_t index_offset;              // index data offset in unLZMAed data(strings starts from 0)
    uint32_t index_size;                // index size when LZMAed
    uint16_t field_28;
    uint16_t field_2a;
    uint16_t files_field_2c;
    uint16_t files_diff;
    uint16_t files_opt;
    uint16_t files_del;
    uint16_t dirs_del;
    uint16_t dirs_add;
    uint16_t links_del;
    uint16_t links_add;
    uint16_t criticals_field_3c;
    uint16_t criticals_field_3e;
};

/*
FOTA segment structure:
 struct fota_seg_hdr;
 {
    uint32_t dst_crc;
    uint32_t src_crc;
 } * files_diff;
 {
    uint32_t crc32;
 } * files_field_2c;
 {
    uint32_t crc32;
 } * files_opt;                 // not good to LZMA it so leave outside?
 LZMAed index {
    {
        links_del;
        files_del;
        files_field_2c + files_diff;
        dirs_add + files_opt;
        file_attrs;
    } strings;
    {
        int32_t size_new;       // >= 0, consumes 2 strings
                                // <  0, consumes 1 string
                                // & 0x3fffffff is real size
    } * files_diff;
    {
        int32_t size_new;
    } * files_field_2c;
    {
        uint32_t field_04;
    } * files_opt;
    {
        int32_t size_diff;
    } * files_diff;
    {
        uint32_t attr_off;
    } * (files_diff + files_field_2c);
    {
        uint32_t attr_off;
    } * (files_opt + dirs_add + links_add);
    {
        uint32_t delta_size;     // XXX: NG!!! shoud start after LZMAed index but no matches.
    } * files_diff;
    {
        uint32_t delta_size;
    } * files_opt;
 };
LZMAed data * N;
 */