MPC885 PowerQUICC Family Reference Manual, Rev. 2
Freescale Semiconductor
39-1
Chapter 39
ATM Controller
This chapter describes the address mapping mechanisms of the ATM controller to support connection
tables for both single- and multi-PHY interfaces, and the commands provided to control ATM transmit and
receive operations on a channel-by-channel basis.
39.1
Address Mapping
Three methods for mapping incoming cell header addresses to local ATM channel numbers are available.
The first method is based on an internal look-up table and is used when the maximum number of ATM
receive connections can be handled by the internal channels. When more than 31 receive connections are
required (extended channel mode), two methods for address mapping are supported: address compression
and the use of content addressable memory (CAM).
Only one address mapping method can be used at a time, and it should be selected in the parameter RAM
(see the EXT and ACP field descriptions in
Section 38.2, “SAR Receive State Register (SRSTATE)”
)
during system start-up. The following sections describe each address mapping method.
39.1.1
Internal Look-up Mechanism (SRSTATE[EXT] = 0)
The internal look-up mechanism maps the address fields in the header of incoming cells to internal channel
numbers. This mapping mechanism uses two tables: an address matching table and a pointing table. The
matching table contains up to thirty-one 32-bit address (GFC/VPI/VCI/PTI/CLP) entries and one empty
entry at the base of the table reserved for the raw cell queue. (Generally, channel number 0 is used for the
raw cell queue as a convention.) The pointing table contains thirty-two 16-bit RCT base address pointers
corresponding one-to-one with the address matching table entries.
NOTE
When a cell is received, the cell header is masked by performing bitwise
AND logic with HMASK in the parameter RAM (see
Table 38-8
). The
resulting masked header is then compared with each entry in the matching
table starting from the top (AMEND). When an entry matches, the parallel
entry in the pointing table is then read to get the RCTn base address of the
local channel n assigned to the incoming cell’s address. If, however, the
address matching algorithm reaches the bottom of the table (AMBASE)
without a match, the incoming cell is directed to the default raw cell queue;
that is, the base address of RCT0 should be placed in the corresponding last
entry of the pointing table (APBASE).
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