2.3.5. Disable Security

The Disable Security (DS) bit removes the security support of the Distributor. It can be set by Secure software during the boot sequence or be configured to be always set when you configure the design. This configuration option must be used when the system does not have the concept of security to allow access to important registers. If you run software without security awareness on a system that supports security, then the Secure boot code can set DS before switching to a Non-secure exception level to run the software. This enables you to program the GIC-500 from any exception level and use two interrupt groups, Group 0 and Group 1. This means that interrupts can target both the FIQ and IRQ handlers on a core.

You must take care when deciding to write security-unaware software using Group 0, as it might not be portable to systems with a concept of security. This is because Group 0 is always Secure in systems with security. It is most portable for security-unaware software to always use Group 1.

If a system has a concept of security but one or more cores do not, then you must not set DS. Instead each core is only able to enable the interrupt groups corresponding to the security states that it supports.

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