ARM AMBA NIC-301 - Manual (Page 30)

Functional Description
ARM DDI 0397G Copyright © 2006-2010 ARM. All rights reserved. 2-15
ID031010 Non-Confidential
FIXED bursts
The AMBA Network Interconnect converts FIXED bursts to one or more INCR1 or INCRn
bursts depending on the downsize ratio. Table 2-6 shows how the network converts FIXED
bursts when it downsizes them.
The AMBA Network Interconnect optimizes unaligned fixed bursts. If an unaligned input fixed
burst maps onto a single output beat, then the output is a fixed burst of the optimal size.
Bypass merge
You can configure the downsizer function to have a programmable bit named
bypass_merge
. If
bypass_merge
is asserted, the network does not perform any packing of beats to match the
optimum SIZE, up to the output data width SIZE.
An aligned input burst means that the address is aligned to the input data width word boundary
after the network aligns it to the transfer size. An unaligned input burst means that the address
is not aligned to the input data width word boundary, even after the network aligns it to the
transfer size.
If a transaction passes through, this means that the downsize function does not change the input
transaction size and type.
Note
• If an exclusive transaction is split into multiple transactions at the output of the downsizer,
the exclusive flag is removed and the master never receives an EXOKAY response.
Response priority is the same as for the upsize function. See Upsizing data width function
on page 2-12.
• In the following example, the input data width is 128-bit and the output data width is
64-bit unless otherwise stated.
Acceptance capability
You can configure the acceptance capability to 1-32 read transactions and 1-32 write
transactions. The maximum issuing capability is (ratio x acceptance capability +1).
2.3.3 FIFO and clocking function
If you configure the network as a clock frequency crossing bridge, then a FIFO function is also
configured.
Note
You can configure the buffering for multiple outstanding transactions even if you are using a 1:1
clocking ratio.
Table 2-6 Conversion of FIXED bursts by the downsize function
FIXED burst type Converted to
FIXED1 INCR2
FIXED2 INCR2 + INCR2 + ...