MPC8280 datasheet(1001/1386 Pages) FREESCALE

1001 / 1386 page

ATM Controller and AAL0, AAL1, and AAL5

MPC8280 PowerQUICC II Family Reference Manual, Rev. 1

Freescale Semiconductor

31-41

31.10.2 Connection Tables (RCT, TCT, and TCTE)

The receive and transmit connection tables, RCT and TCT, store host-initialized connection parameters

after connection set-up. These include AAL type, connection traffic parameters, BD parameters and

temporary parameters used during segmentation and reassembly (SAR). The transmit connection table

extension (TCTE) supports special connections that use ABR, VBR or UBR+ services. Each connection

table entry resides in a 32-byte space. Table 31-15 lists sizes for RCT, TCT, and TCTE.

NOTE

An ATM channel is considered internal if its tables are in an internal

dual-port RAM; it is considered external if its tables are in external

memory.To improve performance, store parameters for fast channels in

internal dual-port RAM and parameters for slower channels in external

memory. Connection tables for external channels are read and written from

external memory each time the CP processes a cell. The CP does, however,

minimize memory access time by burst fetching the 32-byte entry and

writing back only the first 24 bytes.

In all connection tables, fields which are not used must be cleared.

31.10.2.1 ATM Channel Code

Each ATM channel has a channel code used as an index to the channel’s connection table entry. The first

channel in the table has channel code one, the second has channel code two, and so on. Codes of 255 or

less indicate internal channels; codes greater than 255 indicate external channels. Channel code one is

reserved as the raw cell queue and cannot be used for another purpose. The channel code is used to specify

—

Reserved, should be cleared.

ALM

Address look-up mechanism. See Section 31.4, “VCI/VPI Address Lookup Mechanism.”

0 External CAM lookup.

1 Address compression.

1 MPC8264 and MPC8266 only: GMODE[REM] must be set to disable receive emergency mode. If receive emergency

mode were enabled, it would result in IMA transmit protocol violations in cases of system overload, potentially avoiding

protocol errors in the IMA receiver at the expense of generating IMA transmit protocol violations to the far end. Rather

than causing erratic transmit operation, it is better to set GMODE[REM] and deal with the IMA receive protocol

violations locally. Note further that the system should be designed such that overload problems never occur in the

field; any errors due to overload should be eliminated during system design and debug.

Table 31-15. Receive and Transmit Connection Table Sizes

ATM Service Class

RCT

TCT

TCTE

CBR, UBR service

32 bytes

—

ABR, VBR, UBR+ service

32 bytes

Table 31-14. GMODE Field Descriptions (continued)

Bits

Name

Description

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