MPC8280 datasheet(1179/1386 Pages) FREESCALE

1179 / 1386 page

Inverse Multiplexing for ATM (IMA)

MPC8280 PowerQUICC II Family Reference Manual, Rev. 1

Freescale Semiconductor

34-33

0x24

LINK_LD

Word

Bit array identifying which of the “added” links in this group has a

Longer propagation Delay (LD) than any of the existing links. A “1” in

the corresponding link’s bit position indicates that it has a longer

propagation delay. Microcode-managed parameter. Initialize to zero at

group startup.

0x28

CELL_COUNT

Byte

Number of cells received on the TRL while in the Group Delay Sync.

stage. Used only when IDCR-regulated cell processing is used (i.e.

IGRCTNL[IDCR]=1). Used for determining TRLR. When

CELL_COUNT = 128, TRLR is calculated and can be used for

programming IDCR timer values. Microcode-managed parameter.

Initialize to zero at group startup.

0x29

RVPHYNUM

Byte

Receive Virtual PHY number. Maps this IMA receive group to a virtual

PHY number for the purpose of address mapping of received cells.

Note that this parameter must be unique; it must not conflict with the

PHY number of any non-IMA PHYs or with the RVPHYNUM of any

other IMA group.

If there are any PHY numbers which will never be used in a system (i.e.

the actual PHY with the address does not exist), then RVPHYNUM

should be selected from one of these PHYs. If no such PHY numbers

are available (i.e. the multi-PHY interface consists of the full 31 PHYs),

then select RVPHYNUM from one of the PHY numbers of the PHYs

within this IMA group.

0x2A

STALL_THR

Byte

Stall threshold. Used to detect stalled links when performing

round-robin cell extraction from the delay compensation buffers (Dcbz).

This is the number of cells which may be received without advancing

the cell extraction pointer.

The value is application-dependent and must be tuned by the user to

the “expected worst case.” Its value depends on the depth of queues

and FIFOs in the complete transmit/receive path, and the ’burstiness’

of the behavior of the FIFOs. Assuming very bursty FIFOs, it is

approximately:

STALL_THR = 2 x RNUMLINKS x (3 + RX_FIFO)

where:

a) RNUMLINKS is the number of links in the receive group order

structure (regardless of link status).

b) RX_FIFO is the depth of the receive FIFOs of the TC layer.

c) 3 is the rounded value of the allowed transmit skew between links of

a group (2.5, per the IMA standard).

An optimal value for STALL_THR will be great enough to produce no

link stall events in normal operation, but low enough to detect a failed

link as quickly as possible.

0x2B

IRGFS

Byte

IMA Receive Group Frame Size

Bits 0-5: Reserved

Bits 6-7 - GSC_M: Value of received ICP cell Group Status Contl field

(Bits 1:0) which determine the IMA frame size. This field must be

programmed before links in the group are assigned

0x2C

—

Word

Reserved. Must be initialized to zero at group startups.

Table 34-10. IMA Group Receive Table Entry (continued)1

Offset

Name

Width

Description

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