3.3.1 Control Override Register

This register provides a fail-safe override for some CCI-550 functions. Use this register to resolve problems that you cannot work around in another way.

Usage constraints
If you have to write to this register, you must do so before issuing any shareable transactions or DVM messages to the CCI-550. For example, you can do it very early in the boot sequence before installing any Secure OS.
You can access this register using Secure transactions only, irrespective of the programming of the 3.3.2 Secure Access Register.
Available in all CCI-550 configurations.
See 3.2 Register summary for more information.
The following figure shows the bit assignments.
Figure 3-1 ctrl_ovr register bit assignments
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The following table shows the bit assignments.

Table 3-2 ctrl_ovr register bit assignments

Bits Name Function
[31:5] -
[4] cd_layer2_ace_enable
Enable both snoop data layers for data transfer between ACE masters.
This bit applies when a second CD channel is available, that is, when the CCI-550 is configured with a dual-layer snoop data network.
0ACE masters use the single CD channel.
1ACE masters can use either CD channel.


A value of 1 for this bit does not guarantee that a second CD channel is configured. Setting this bit where the CCI-550 is configured with a single-layer snoop data network has no effect.
If you set this bit to 1, the CCI-550 does not support the Continuous_Cache_Line_Read_Data ACE property. Some ACE masters rely on this property and setting this bit to 1 might cause system deadlock. However, the following ARM processors are known to work with this bit set to 1:
  • Cortex®-A32, Cortex-A35, Cortex-A53.
  • Cortex-A57, Cortex-A72.
[3] disable_clock_gating
Disable regional clock gating:
0Regional clock gating operates in the CCI-550. See 1.7 Test features and 2.3 Clocking and reset.
1Disable regional clock gating in the CCI-550.
[2] disable_snoop_filter
Disable the snoop filter:
0Snoop filter operation is defined by the power state input, PSTATE.
1Disable snoop filter operation.
[1] dvm_message_disable
DVM message disable:
0Send DVM messages according to the Snoop Control Registers.
1Disable propagation of all DVM messages.
[0] snoop_disable
Snoop disable:
Send snoop requests according to the Snoop Control Registers.
Disable all snoops but not DVM messages.
Related concepts
2.4.3 Snoop connectivity and control
Related reference
3.3.10 Snoop Control Registers
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