Altera RapidIO MegaCore Function - Manual (Page 62)

4–16 Chapter 4: Functional Description
Physical Layer
RapidIO MegaCore Function August 2014 Altera Corporation
User Guide
■ Control symbol error —if an embedded or packet-delimiting control symbol is
errored, the Physical layer flags the error. The packet in which the errored control
symbol is embedded should be retransmitted by the link partner as part of the
error recovery process.
■ Character error—if the Physical layer receives an errored character (an invalid 10-
bit code, or a character of wrong disparity) or an illegal character (any control
character other than the non-delimiting Start of Control (SC) character inside a
packet) within a packet. In this case the Physical layer flags the error and drops the
rest of the packet.
Receive Priority Threshold Values
The Physical layer implements the RapidIO specification deadlock prevention rules
by accepting or retrying packets based on three programmable threshold levels, called
Priority Threshold values. The algorithm uses the packet’s priority field value. The
block determines whether to accept or retry a packet based on its priority, the
threshold values, and the number of free blocks available in the receiver buffer, using
the following rules:
■ Packets of priority 0 (lowest priority) are retried if the number of available free
64-byte blocks is less than the Priority 0 Threshold.
■ Packets of priority 1 are retried only if the number of available free 64-byte blocks
is less than the Priority 1 Threshold.
■ Packets of priority 2 are retried only if the number of available free 64-byte blocks
is less than the Priority 2 Threshold.
■ Packets of priority 3 (highest priority) are retried only if the receiver buffer is full.
The default threshold values are:
■ Priority 2 Threshold = 10
■ Priority 1 Threshold = 15
■ Priority 0 Threshold = 20
You can specify other threshold values by turning off Auto-configured from receiver
buffer size
on the Physical Layer page in the RapidIO parameter editor.
The RapidIO parameter editor enforces the following constraints to ensure the
threshold values increase monotonically by at least the maximum size of a packet
(five buffers), as required by the deadlock prevention rules:
■ Priority 2 Threshold > 9
■ Priority 1 Threshold > Priority 2 Threshold + 4
■ Priority 0 Threshold > Priority 1 Threshold + 4
■ Priority 0 Threshold < Number of available buffers