Freescale Semiconductor MPC8260 - Manual (Page 934)

ATM Controller and AAL0, AAL1, and AAL5
MPC8260 PowerQUICC II Family Reference Manual, Rev. 2
30-14 Freescale Semiconductor
30.4.1 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 30-3 , 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 30-4 , is a 32-bit entry (16-bit channel code and a match-status
bit).
The external CAM fields are described in Table 30-2 .
0 3 4 15 16 31
PHY Addr
(MPHY)
GFC + VPI VCI
Figure 30-3. External CAM Data Input Fields
0 1 15 16 31
MS — Channel Code
Figure 30-4. External CAM Output Fields
Table 30-2. 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.
MS Match status.
0 Match was found.
1 Match was not found.