SEPTENTRIO PolaRx5TR, Справочное руководство

Страница: 295 / 512

4 SBF Reference
4.1 SBF Outline
SBF is the binary output format of Septentrio receivers. In this format, the data are arranged
in binary blocks referred to as SBF blocks.
Each SBF block consists of a sequence of numeric or alphanumeric fields of different types
and sizes. The total block size is always a multiple of 4 bytes.
The fields of an SBF block may have one of the following types:
Type Description
u1 Unsigned integer on 1 byte (8 bits)
u2 Unsigned integer on 2 bytes (16 bits)
u4 Unsigned integer on 4 bytes (32 bits)
u8 Unsigned integer on 8 bytes (64 bits)
i1 Signed integer on 1 byte (8 bits)
i2 Signed integer on 2 bytes (16 bits)
i4 Signed integer on 4 bytes (32 bits)
i8 Signed integer on 8 bytes (64 bits)
f4 IEEE float on 4 bytes (32 bits)
f8 IEEE float on 8 bytes (64 bits)
c1[X] String of X ASCII characters, right padded with bytes set to 0 if needed.
Each multi-byte binary type is transmitted as little-endian, meaning that the least significant
byte is the first one to be transmitted by the receiver. Signed integers are coded as two’s
complement.
Every SBF block begins with an 8-byte block header, which is followed by the block body.
4.1.1 SBF Block Header Format
Every SBF block starts with an 8-byte header having the following contents:
Parameter Type Description
Sync
c1[2] The Sync field is a 2-byte array always set to 0x24, 0x40. The first byte of every SBF block has hexadecimal
value 24 (decimal 36, ASCII ’$’). The second byte of every SBF block has hexadecimal value 40 (decimal 64,
ASCII ’@’). These two bytes identify the beginning of any SBF block and can be used for synchronization.
CRC
u2 The CRC field is the 16-bit CRC of all the bytes in an SBF block from and including the ID field to the last byte
of the block. The generator polynomial for this CRC is the so-called CRC-CCITT polynomial:
x
16
+ x
12
+ x
5
+ x
0 .
The CRC is computed in the forward direction using a seed of 0, no reverse and no final XOR.
ID
u2 The ID field is a 2-byte block ID, which uniquely identifies the block type and its contents. It is a bit field with
the following definition:
bits 0-12: block number;
bits 13-15: block revision number, starting from 0 at the initial block definition, and incrementing each time
backwards-compatible changes are performed to the block (see section 4.1.6).
Length
u2 The Length field is a 2-byte unsigned integer containing the size of the SBF block. It is the total number of
bytes in the SBF block including the header. It is always a multiple of 4.
4.1.2 SBF Block Names and Numbers
The structure and contents of an SBF block are unambiguously identified by the block ID.
For easier readability, a block name is also defined for each block. When invoking the
setSBFOutput
command to enable a given block, the block name should be specified.
295