IDT CPS-1848, Руководство пользователя

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2. RapidIO Ports > Multicast Event Control Symbols
CPS-1848 User Manual 39 June 2, 2014
Formal Status This document is confidential and is subject to an NDA.
Integrated Device Technology
Priority 0, 1 and 2 packets all have buffer allocation values associated with them. These flow control values are called
“watermarks”, a shortened form of “high watermark”: the highest point on shore that water reaches. The watermark associated
with a specific priority determines when a buffer is too full to accept/transmit packets of a specific priority. Note that there is no
watermark for priority 3 packets, since priority 3 packets must always be accepted whenever buffers are available.
When transmitter-controlled flow control is active on a port, the transmitter must have watermark values for the packets which
it transmits to the receiver. The watermarks reside in the
Port {0..17} Watermarks Register . These watermarks define the
number of available buffers at which point packets of that priority will stop being transmitted. If a system is rarely congested,
the default values for this register will deliver optimal performance.
2.5 Multicast Event Control Symbols
Multicast Event Control Symbols (MECS) distribute events with low latency and little variability in distribution delays throughout
a RapidIO system. An MECS can be received by a CPS-1848 port, or can be triggered by the MCAST pin on the device. Once
an MECS event has been received/triggered, the MECSs are transmitted by each port with the MCAST_CS field set to one in
the
Port {0..17} Control 1 CSR . Note that the port which received the MECS does not transmit the MECS.
2.6 Port Reconfiguration Operations
When one of the following port configuration events occur, a CPS-1848 port will require a re-initialization or reset (see Table 6 ).
The watermark values in the Port {0..17} Watermarks Register should be set based on the buffer size of
the link partner and the required traffic characteristics for packets of each priority. The default values
will result in optimal throughput when traffic is bursty and congestion is rare in the system, as they
maximize the number of low priority packets that can be accepted. When congestion is normal and
traffic of a specific priority must have guaranteed throughput, adjust the watermark values to reserve
sufficient buffers in the link partner. Depending on the link latency, two or three buffers per congested
priority must be reserved to ensure line rate throughput.
The CPS-1848 provides a physical pin called MCAST that can generate an MECS to all Multicast Event
participant egress ports (for more information, see the CPS-1848 Datasheet).
If two or more MECSs are received close enough in time that more than one is waiting for transmission
on a port, then at least one of them is forwarded. The other(s) may not be (For information on minimum
period duration between MECSs, see
Multicast-Event Control Symbol (MECS) Latency ). The most
recently received MECS will be transmitted. Regardless of how many MECSs are received under these
conditions, at least one will be transmitted from each participant port.
Table 6: Port Reconfiguration Operations
Port Configuration Event Recommended Port Operation
Quadrant Configuration Register change Port reset (see PORT_SEL in Device Reset and Control
Register )
PLL {0..11} Control 1 Register .PLL_DIV_SEL change PLL reset (see PLL_SEL in Device Reset and Control
Register )
Lane {0..47} Control Register .TX_RATE or RX_RATE
Lane rate change
Port reset (see PORT_SEL in Device Reset and Control
Register ). For examples of reconfiguring port and lane
speeds, see Lane and Port Speeds .
Port {0..17} Error and Status CSR .IDLE2_EN change Port reset (see PORT_SEL in Device Reset and Control
Register )