ARM AMBA NIC-301 - Manual (Page 29)

Functional Description
ARM DDI 0397G Copyright © 2006-2010 ARM. All rights reserved. 2-14
ID031010 Non-Confidential
Acceptance capability
You can configure the upsizer to support 1-32 read transactions and 1-32 write transactions. The
issuing capability is a maximum of twice the acceptance capability.
2.3.2 Downsizing data width function
The downsize function reduces the data width by the following ratios:
•
2:1
• 4:1
• 8:1.
The downsizer does not merge data narrower than the destination bus if the transaction is
marked as non-cacheable.
This section describes the following:
•
INCR bursts
• WRAP bursts
• FIXED bursts on page 2-15
• Bypass merge on page 2-15
• Acceptance capability on page 2-15.
INCR bursts
The AMBA Network Interconnect converts INCR bursts that fall within the maximum payload
size of the output data bus to a single INCR. It converts INCR bursts that are greater than the
maximum payload size of the output data bus to multiple INCR bursts. Table 2-5 shows how the
network converts INCR bursts when it downsizes them.
INCR bursts with a size that matches the output data width pass through unconverted.
The AMBA Network Interconnect packs INCR bursts with a SIZE smaller than the output data
width to match the output width whenever possible, using the upsize transfer function. See
Upsizing data width function on page 2-12.
WRAP bursts
The AMBA Network Interconnect always converts WRAP bursts to WRAP bursts of twice the
length, up to the output data width maximum size of WRAP16, in which case, it treats the
WRAP burst as two INCR bursts that can each map onto one or more INCR bursts.
Table 2-5 Conversion of INCR bursts by the downsize function
INCR burst type Converted to
Aligned INCR4 INCR8
Unaligned INCR4 INCR7
Aligned INCR9 INCR15 + INCR2