IDT88K8483 Integrated Device Technology, IDT88K8483 Datasheet - Page 53

• Manufacturer Part Number: IDT88K8483
• Description: Spi-4 Exchange Document Issue 1.0
• Manufacturer: Integrated Device Technology

in the
the data buffer to the egress port buffer. If the burst mode is not enabled, then the LID can transfer only one segment of data at a time from the data
buffer to the egress port buffer, and the PFP can schedule the next segment for the LID only after the current segment has been transmitted. When
CREDIT_EN field in the
configured in the MAX_BURST_S field in the
MAX_BURST_H field in the
PKT_MODE in the
mode the scheduler schedule the whole packet. When the egress is packet mode, and it receives back-pressure in the middle of sending a packet, it
finishes sending the current packet before stalling any subsequent packets queued for transmission.
PFP Flow Control
PFP Ingress Flow Control for non over booking mode
normal operation there are enough free segments, so the LID status is starving, and the SPI-4 ingress interface is sending starving status to the adja-
cent device through the status bus. When the number of free segments is less than THR_STARV (for example 100 segments), the LID status is
changed to hungry, and the SPI-4 ingress interface starts sending hungry status to the adjacent device. When the number of free segments is less
than THR_HUNG (for example 50 segments), the LID status is changed to satisfied, and the SPI-4 ingress interface starts sending satisfied status to
the adjacent device.
4 ingress interface starts sending hungry status to the adjacent device through the status bus. When the number of free segments is again more than
THR_STARV (for example 100 segments), the LID status is changed to starving, and the SPI-4 ingress interface starts sending starving status to the
adjacent device.
SPI-4 interface as shown in
interface, and the PFP LID status information from the PFP logic. The device gets the flow control mode from the EBP_EN field in the
Packet Mode Control Registers (p. 123).
IDT IDT88K8483
The egress also has the flexibility to be programmed for burst or non-burst mode and status or credit mode transfer control. When BURST_EN field
The maximum burst size can be configured separately for starving status and for hungry status. The maximum burst size for starving status is
The egress can be programmed to interleave packet mode and packet mode. The packet mode for each LID is configured by setting to 1 the
There are 3 main parameters for configuring the SPI-4 ingress flow control for non over booking mode:
- Maximum number of segments per LID is configured in M field in the
- Starving Free segments per LID is configured in THR_STARV field in the
- Hungry Free segments per LID is configured in THR_HUNG field in the
There are three status options per LID in the SPI-4 ingress PFP: starving hungry and satisfied. In SPI-4 ingress PFP for LP0 (for example), in
When the number of free segments is again more than THR_HUNG (for example 50 segments), the LID status is changed to hungry, and the SPI-
According to the status information from the QDR-II LID, the PFP LID, and the flow control mode the device generates the status indication to the
PFP Flow Control Register (p. 125)
PFP Egress Packet Mode Control Registers (p.
PFP Flow Control Register (p. 125)
PFP Egress Burst Size Table (p.
Table 3: “SPI-4 Status Information” (p.
See more information about the PFP/QDR-II flow control in the
is set to 1, the burst mode is enabled, and the same LID can transfer more than one segment of data from
PFP Egress Burst Size Table (p.
LID 1
LID 0
Figure 21 PFP Ingress Flow Control Example
PFP (508 segments, 127K bytes)
sets to 1, the credit mode is enabled, and the device uses the LID credit.
122).
53 of 162
123). In interleave mode the scheduler schedules parts of the packet. In packet
Satisfied
Starving
Satisfied
Starving
Hungry
Hungry
PFP Buffer Segment Assign Table (p.
56). The device gets the QDR-II LID status information from the QDR-II
PFP Buffer Segment Assign Table (p.
PFP Buffer Segment Assign Table (p.
122). The maximum burst size for hungry status is configured in the
Maximum number of segments assigned to LID 1 = 256
Maximum number of segments assigned to LID 0 = 256
Hungry free segments assigned to LID 0 = 50
Starving free segments assigned to LID 0 = 100
Hungry free segments assigned to LID 1 = 50
Starving free segments assigned to LID 1 = 100
QDR-II Flow Control (p.
120).
120).
120).
October 20, 2006
56).
PFP Egress