MPC8280 datasheet(974/1386 Pages) FREESCALE

974 / 1386 page

ATM Controller and AAL0, AAL1, and AAL5

MPC8280 PowerQUICC II Family Reference Manual, Rev. 1

31-14

Freescale Semiconductor

31.4.1

External CAM Lookup

An external CAM is usually used when the range of VCI/VPI values varies widely or is unknown. Clearing

GMODE[ALM] selects the external CAM address lookup mechanism. If there is no match in the external

CAM, the cell is considered a misinserted cell. The external CAM can point to internal or external channels

(channels whose connection table resides in external memory). The CAM input, shown in Figure 31-3, is

the 32-bit cell address: PHY address, GFC + VPI, and VCI.

NOTE

The bus atomicity mechanism for CAM accesses may not function correctly

when the CPM performs a DMA access to an external CAM device. This

only impacts systems in which multiple CPMs will access the CAM.

The output of the CAM, shown in Figure 31-4, is a 32-bit entry (16-bit channel code and a match-status

bit).

The external CAM fields are described in Table 31-2.

PHY Addr

(MPHY)

GFC + VPI

VCI

Figure 31-3. External CAM Data Input Fields

15 16

—

Channel Code

Figure 31-4. External CAM Output Fields

Table 31-2. External CAM Input and Output Field Descriptions

Field

Description

PHY Addr

In multiple PHY mode, this field contains the 4 least-significant bits of the current channel’s physical

address. Because this CAM comparison field is limited to 4 bits, two CAM devices are needed if using

more than 16 PHYs.The msb of the PHY address (bit 4) selects between the two devices. If the msb is

zero, the CP accesses the CAM whose address is written in the EXT_CAM_BASE parameter in the

parameter RAM; if the msb is set, the CP uses EXT_CAM1_BASE. See Section 16.4.1, “CMX UTOPIA

Address Register (CMXUAR).”

In single PHY mode, clear this field.

GFC+VPI,

VCI

The GFC, VPI, and VCI of the current channel.

Ch Code

Pointer to internal or external connection table.

—

Reserved, should be cleared.

Match status.

0 Match was found.

1 Match was not found.

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