Motorola PowerQUICC II MPC8280 Series Reference Manual page 1059

Table 31-15. Receive and Transmit Connection Table Sizes
ATM Service Class
CBR, UBR service
ABR, VBR, UBR+ service
An ATM channel is considered internal if its tables are in an
internal dual-port RAM; it is considered external if its tables
are in external memory.To improve performance, store
parameters for fast channels in internal dual-port RAM and
parameters for slower channels in external memory.
Connection tables for external channels are read and written
from external memory each time the CP processes a cell. The
CP does, however, minimize memory access time by burst
fetching the 32-byte entry and writing back only the first 24
bytes.
In all connection tables, fields which are not used must be
cleared.
31.10.2.1 ATM Channel Code
Each ATM channel has a channel code used as an index to the channel's connection table
entry. The first channel in the table has channel code one, the second has channel code two,
and so on. Codes of 255 or less indicate internal channels; codes greater than 255 indicate
external channels. Channel code one is reserved as the raw cell queue and cannot be used
for another purpose. The channel code is used to specify a VC when sending a
command, initiating the external CAM or address compression tables, and when
TRANSMIT
the CP sends an interrupt to an interrupt queue.
Example:
Suppose a configuration supports 1,024 regular ATM channels. To allocate 4 Kbytes of
dual-port RAM space to the internal connection table, determine that channel codes 0–63
are internal (64 VCs × 64 bytes (RCT and TCT) = 4 K). Channels 0–1 are reserved. The
remaining 962 (1024 - 62) external channels are assigned channel codes 256–1217. See
Figure 31-24.
MOTOROLA Chapter 31. ATM Controller and AAL0, AAL1, and AAL5
Freescale Semiconductor, Inc.
RCT
32 bytes
32 bytes
NOTE
For More Information On This Product,
Go to: www.freescale.com
ATM Memory Structure
TCT TCTE
32 bytes —
32 bytes 32 bytes
ATM
31-45