Freescale Semiconductor MPC8260 - Manual (Page 936)

ATM Controller and AAL0, AAL1, and AAL5
MPC8260 PowerQUICC II Family Reference Manual, Rev. 2
30-16 Freescale Semiconductor
to indicate the received cell’s channel code. Address compression field descriptions are shown in
Table 30-3 .
30.4.2.1 VP-Level Address Compression Table (VPLT)
The size of the VP-level table depends on the number of mask bits in VP_MASK. For example, if only
one PHY is available (PHY address = 0) and VPMASK = 0b11_1111_1111, VP pointer contains ten bits
and the table is 4 Kbytes. Because each VPLT entry is 4 bytes, the address of an entry is VPT_BASE + VP
pointer
× 4.
Each VPLT entry has two parameters:
• VC_MASK—A 16-bit VC-level mask for masking the incoming cell’s VCI
• VCOFFSET—A 16-bit VC-level table offset from VC_BASE that points to the appropriate
VC-level table’s (VCLT) starting address. The address of the VCLT is VC_BASE + VCOFFSET
× 4.
If the VCLTs are to be placed contiguously in memory, each table’s VCOFFSET depends on the
size of preceding tables. Each table’s size depends on the number of ones in VC_MASK.
Figure 30-6 gives the general formula for determining VCOFFSET.
Table 30-4 shows example VCOFFSET calculations for a VP-level table with four entries.
Table 30-3. Field Descriptions for Address Compression
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 comparison field is limited to 4 bits, two sets of look-up tables are needed if using
more than 16 PHYs.The msb of the PHY address (bit 4) selects between the two sets of tables. If the msb
is zero, the CP accesses the tables at VPT_BASE and VCT_BASE; if the msb is set, the CP uses
VPT1_BASE and VCT1_BASE. See
Section 16.4.1, “CMX UTOPIA Address Register (CMXUAR) .”
In single PHY mode, clear this field.
VCI, VPI The VCI and VPI 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.
General formula: VCOFFSET
(n+1)
= VCOFFSET
n
+ 2 (number of ones in VC_MASKn)
Figure 30-6. General VCOFFSET Formula for Contiguous VCLTs
Table 30-4. VCOFFSET Calculation Examples for Contiguous VCLTs
VP-Level
Table Entry
VC_MASK
Number of Ones
in VC_MASK
VC-Level
Table Size
VCOFFSET
0 0x0237 6 2
6
= 64 entries 0
1 0x0230 3 2
3
= 8 entries 64