Altera SerialLite II Protocol - Manual (Page 41)

Altera Corporation 41
SerialLite II Protocol Reference Manual
SerialLite II Specification
f
Refer to “Effect of Link Management Packet Corruption” on page 2–64
and “Effect of Link Management Packet Corruption” on page 2–69 for
details.
Idle Generation
The transmitter sends idles across the link when there is no packet
information or special ordered sets to be sent.
There are four scenarios where IDL characters are transmitted:
1. During the link initialization and training. See “Link Initialization
and Training” on page 2–27 for more information.
2. There is no user data to transmit and idles are needed as
inter-packet fill, as shown in
Figure 2–20 .
Figure 2–20. Idle Used as Inter-Packet Fill
The current packet must finish or be interrupted with a break-packet
sequence. The transmission of regular packet data can be resumed
with the CDP or start of a user packet (SDP or SPP). Either all zero
bytes or the special /IDL/ characters are injected between packets.
The idle data must be ignored and dropped by the receiver. All
running disparity errors are counted as a data error as the status of
the link is monitored.
To reduce EMI, sending all zero ordered sets as inter-packet fill with
scrambling enabled is recommended. This option eliminates
repeating characters, which has great effect at high data rates.
For simpler implementations, the transmitter could choose to inject
only
||IDL|| ordered sets between packets or segments. The receiver is
required to discard all zero ordered sets between packet segments
without raising an error.
3. When data or priority packets are interrupted at the system
interface, or when the transmit link layer device under-runs, or
when the flow control command is received.
SDP User Data EGP Idle Idle SDP User Data EGP Idle