Apc Scheduling Tables - Freescale Semiconductor MPC850 User Manual

APC Scheduling Tables

If the UTOPIA port is not used, the APCST parameter on parameter page 4 must indicate
that the APC on page 4 is disabled and must also point to the active APC page(s). This is
accomplished using the APCST[NSER,CSER] mechanism described in Section 40.3,
"Using the APC with Multiple ATM Ports." The APC on parameter page 4 can be disabled
by setting APCST[DIS].
40.5 APC Scheduling Tables
An APC scheduling table is a memory space located in the dual-port RAM. The user
determines the number of entries in the APC scheduling table based on the required traffic
parameters. The APC can be configured to handle two levels of priority. The APC first
schedules channels from the first priority table, scheduling up to NCITS channels from the
APCT_PTR1 slot. If there are fewer than NCITS channels in this slot, the APC tries to
select the rest of the channels from the second priority table. The total number of channels
selected from tables is always NCITS or less. On each APC timeout, the APC advances the
real-time pointers of tables by one slot.
Note that during initialization all entries in the APC scheduling tables (from APCT_BASEx
to APCT_ENDx) must be loaded with 0xFFFF (invalid channel number) to indicate an
empty slot. The APC scheduling tables are shown in Figure 40-4.
.
First Priority Table
Second Priority Table
APCT_BASE1
APCT_BASE2
APCT_PTR1
APCT_PTR2
APCT_END1
APCT_END2
Half word
Half word
Note: APCT_END points to one position after
the last entry in the table
Figure 40-4. APC Scheduling Tables
Note that the scheduling tables need not be the same length; the length of the table affects
only the minimum programmable transmit rate, which might be different for high-priority
or low-priority channels.
Chapter 40. ATM Pace Control