RapidIO: The Next Generation Communication Fabric For Embedded Application

8.2. CONTROL SYMBOL FORMATS

Control symbols are used for packet delineation, transmission, pacing, and other link interface control functions by the RapidIO parallel physical layer.

Control symbols used by the RapidIO parallel interface are 32 bits in length. Although they are 32 bits long, the control symbol is actually a 16-bit quantity that is sent twice. The second 16 bits are an inverted version of the first 16 bits. Figure 8.3 shows the format of the control symbols. From this diagram it is clear that bits 16–31 are inverted representations of bits 0–15. Because of the width of the parallel interface and the fact that data is transmitted at twice the clock rate, the time it takes to transmit a full control symbol is two clock cycles for the 8-bit interface and one clock period for the 16-bit interface. The 32-bit length also ensures that all packets and control symbols are properly aligned to 32-bit boundaries at all times.

This control symbol format is displayed in Figure 8.3. Bits 13–15 and 29–31 contain a field that defines the type of the control symbol. This 3-bit field can encode eight separate types. Six control symbol types are defined with two encodings remaining (Table 8.1). These encodings are reserved for future expansion use.

Figure 8.3. Parallel RapidIO control symbol format

Table 8.1. Control symbol types

Type	Type encoding	Name	Description
0	0b000	Packet accepted ...