A10.4 CHI channel properties
You can configure the processor to use the CHI protocol for the master memory interface
Table A10-4 CHI channel properties
Property Value Comment
Snoop acceptance
capability
10 The SCU can accept and process a maximum of 10 snoop requests from the system.
DVM acceptance
capability
4
The SCU can accept and process a maximum of four DVM transactions from the system. Each of
these four transactions can be a two part DVM message.
The interconnect must be configured to never send more than four DVM messages to a Cortex‑A35
processor, otherwise the system might deadlock.
Snoop latency Hit
When there is a hit in L2 cache, the best case for response and data is 11 processor cycles. When there
is a miss in L2 cache and a hit in L1 cache, the best case for response and data is 14 processor cycles.
Latencies can be higher if hazards occur or if there are not enough buffers to absorb requests.
Miss Best case six processor cycles when the SCU duplicate tags and L2 tags indicate the miss.
DVM
The cluster takes a minimum of six cycles to provide a response to DVM packets.
Snoop filter Supported The cluster provides support for an external snoop filter in an interconnect. It indicates when clean
lines are evicted from the processor by sending Evict transactions on the CHI write channel. However,
there are some cases where incorrect software can prevent an Evict transaction from being sent,
therefore you must ensure that any external snoop filter is built to handle a capacity overflow that
sends a back-invalidation to the processor if it runs out of storage.
Supported
transactions
- All transactions described by the CHI protocol:
• Are accepted on the CHI master interface from the system.
• Can be produced on the CHI master interface except:
— ReadClean.
— WriteBackPtl.
— WriteCleanPtl.
Related information
Arm® AMBA® 5 CHI Protocol Specification
A10 CHI Master Interface
A10.4 CHI channel properties
100236_0100_00_en Copyright © 2015–2017, 2019 Arm Limited or its affiliates. All rights
reserved.
A10-130
Non-Confidential
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