ATM Controller
MPC885 PowerQUICC Family Reference Manual, Rev. 2
Freescale Semiconductor
39-3
of the second-level tables (SLTs), referred to as the second-level table offset (SLTOFFSET). SLTOFFSET
is an offset from the base address of the second-level tables (SLBASE). In the second-level compression,
the VCI bits are masked with the SLMASK field from the first-level table, and the result is used as an index
pointer into the particular SLT addressed by SLTOFFSET. The SLT entry contains the assigned local
channel number for the received cell.
FLBASE, SLBASE and FLMASK are defined in the parameter RAM; see
Table 38-10
. The following
sections describe the addressing tables and show an example of address compression.
39.1.2.1
First-Level Addressing Table (FLT)
Each entry in the first-level addressing table (FLT) contains a 16-bit second-level mask (SLMASK) which
is used to mask the incoming cell’s VCI. SLMASK should contain a contiguous sequence of ones that
operates in the same way as the FLMASK bit sequence.
NOTE
The SLMASK must contain at least one bit set. Failure to do so results in
having the cells associated with the corresponding VP (VPI x FLMASK)
routed to the raw PHY cell queue. The FLT entry also contains a 16-bit
second-level table offset (SLTOFFSET) that points to a single SLT.
Unused FLT entries should be cleared (null entry). Cells with a null entry pointer are received into the
default raw cell queue.
The size of the FLT depends on the number of mask bits in the FLMASK. If, for example, FLMASK
contains an unbroken sequence of ten bits set, the index pointer into the FLT will contain 10 bits, resulting
in a table size of 4 Kbytes. The actual address of an FLT entry is (index_pointer x 4).
39.1.2.2
Second-Level Addressing Tables (SLTs)
An SLT entry contains the 16-bit local channel number (0-65534) assigned to match a received cell
header’s VCI and VPI. The local channel number corresponds to an RCT, where:
•
Channel number 0—RCT0 is located in the dual-port RAM pointed to by CT_BASE. (Default Raw
Cell queue for PHY 0 or in single PHY mode only.)
•
Channel number 1–31—RCTs for these connections are in the dual-port RAM. The address of each
RCT is (channel_number x 64 + address pointed to by CT_BASE). (Default Raw Cell queues for
PHY 1-31.)
•
Channel numbers greater than 31—RCTs for these connections are in external memory. The
address of each RCT is (channel_number x 64 + ECT_BASE).
The number of entries in each SLT depends on the length of the sequence of ones in SLMASK. For
example, the size of an SLT with a sequence of 10 bits set in the SLMASK is 2 Kbytes. The actual address
of an entry in an SLT is equal to ( SL index_pointer x 2). Note that SLTOFFSET
may be scaled by 4 to increase the number of available SLT entries, (see the description of SLBASE
Table 38-10
).
Summary of Contents for PowerQUICC MPC870
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