PM7367 datasheet(55/323 Pages) PMC

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PM7367 FREEDM-32P32

DATA SHEET

PMC-1991499

ISSUE 2

FRAME ENGINE AND DATA LINK MANAGER

PROPRIETARY AND CONFIDENTIAL TO PMC-SIERRA, INC., AND FOR ITS CUSTOMER’S INTERNAL USE

Receive Packet Queues

Receive Packet Queues are used to transfer RPDRs between the host and the

RMAC. There are three queues: a RPDR Large Buffer Free Queue (RPDRLFQ),

a RPDR Small Buffer Free Queue (RPDRSFQ) and a RPDR Ready Queue

(RPDRRQ). The free queues contain RPDRs referencing RPDs that define free

buffers. The ready queue contains RPDRs referencing RPDs that define buffers

ready for host processing. The RMAC pulls RPDRs from the free queues when

it needs free data buffers. The RMAC places an RPDR onto the ready queue

after it has filled the buffers with data from each complete packet. The host

removes RPDRs from the ready queue to process the data buffers. The host

places the RPDRs back onto the free queues after it finishes reading the data

from the buffers.

When starting to process a packet, the RMAC uses a small buffer RPD to store

the packet data. If the packet requires more than one buffer, the RMAC uses

large buffer RPDs to store the remainder of the packet. The RMAC links

together all the RPDs required to store the packet and returns the RPDR

associated with the first RPD onto the ready queue.

All receive packet queues reside in host memory and are defined by the Rx

Queue Base (RQB) register and index registers which reside in the RMAC. The

Rx Queue Base is the base address for the receive packet queues. Each packet

queue has four index registers which define the start and end of the queue and

the read and write locations of the queue. Each index register is 16 bits in length

and defines an offset from the Rx Queue Base. Thus, as shown in the Figure 6,

the host address of a RPDR is calculated by adding the index register to the Rx

Queue Base register. The host initialises the Rx Queue Base and all the index

registers. When an entity (either the RMAC or the host) removes elements from

a queue, the entity updates the read pointer for that queue. When an entity

(either the RMAC or the host) places elements onto a queue, the entity updates

the write pointer for that queue.

The read index for each queue points to the last valid RPDR read while the write

index points to where the next RPDR can be written. The start index points to the

first valid location within the queue; an RPDR can be written to this location.

However, the end index points to a location that is beyond a queue; an RPDR

can not be written to this location. Note however, the start index of one queue

can be set to the end index of another queue. A queue is empty when the read

index is one less than the write index; a queue is also empty if the read index is

one less than the end index and the write index equals the start index. A queue is

full when the read index is equal to the write index. Figure 6 shows the RPDR

reference queues.

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