1.3 Frame Format

The USI frame format is based on the Serial Communications Profile of the Management Plane defined in the PRIME specification as shown in the figure below.

The frame starts and ends with 0x7E (delimiter). The frame delimiters will be escaped if they appear in message data. The description of each field is as follows:

MSG LENGTH: Length in bytes of the message data (message length, protocol ID and CRC bytes are excluded).
PROTOCOL ID: Protocol in the frame.
MESSAGE DATA: Variable length field that contains the data of the exchanged primitive.
CRC: Error correction code for the message. The CRC field can have a different length depending on the protocol.

Some protocols need data lengths greater that 1024 bytes. To handle this, an additional bit from the Data field is used, as depicted in the following figure:

Figure 1-3. USI Extended Lenght Frame Format

The total length is encoded as the concatenation of XLEN as the most significant bit and the bits from MSG LENGTH.

Along with XLEN, first Data Byte is used to encode a command, which is internal to each protocol using this extended frame format.

Table 1-1. USI Protocols, Associated CRC Size and Length Encoding
Protocol	Description	ID	CRC Size (bits)	Uses XLEN
PROTOCOLS_MNGP_PRIME	Management Plane defined in the PRIME specification	0x00 - 0x07	32	No
PROTOCOL_SNIF_PRIME	PRIME Sniffer	0x13	16	No
PROTOCOL_PHY_SERIAL_PRIME	PRIME PHY serial layer	0x1F	16	No
PROTOCOL_PHY_TESTER	Used for PHY Tester Tool provided with the evaluation kit in order to serialize the API of the PHY layer	0x22	16	No
PROTOCOL_SNIF_G3	G3 Sniffer	0x23	16	No
PROTOCOL_MAC_G3	G3 MAC Layer serialization	0x24	16	No
PROTOCOL_ADP_G3	G3 ADP Layer serialization	0x25	16	Yes
PROTOCOL_COORD_G3	G3 Coordinator serialization	0x26	16	Yes
PROTOCOL_PHY_RF215_TESTER	Used to interact like the PHY tester tool with the RF215 PHY layer	0x28	16	No
PROTOCOL_PRIME_API	PRIME API	0x30	8	Yes
PROTOCOL_MM_AL_API	Meters And More AL API	0x31	8	Yes
PROTOCOL_INTERNAL	Reserved for internal use	0x3E	User defined	User defined
PROTOCOL_USER_DEFINED	Defined by the user if required	0xFE	User defined	User defined