As described in earlier chapters, RapidIO uses packets to send data and control information around within a system. The physical layer specifications describe the portions of the packets that are used to move a packet between adjacent devices. This is often referred to as the data link protocol layer. In both the parallel and serial physical layers, there are 24 bits that are defined as part of the physical layer. These 24 bits are divided into 8 bits of header information and 16 bits of cyclic redundancy check (CRC) code. This section discusses the serial packet format and the fields that are added to a packet by the serial physical layer. Table 7.1 presents the fields added to a packet by the serial physical layer.
7.1.1. Packet Format
Figure 7.1 shows the format of a serial packet and how the physical layer ackID, rsvd, and prio fields are prefixed at the beginning of the packet and the 16-bit CRC field is appended to the end of the packet.
The unshaded fields are the fields added by the physical layer. The shaded field is the combined logical and transport layer bits and fields that are passed to the physical layer. The 3-bit rsvd field is required to make the packet length an integer multiple of 16 bits. The physical layer fields wrap around the transport and logical fields.
Serial RapidIO packets are required to have a length that is an integer multiple of 32 bits. This sizing simplifies the design of the transmit and receive port logic where the internal data ...