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For Secure interrupts, the priority grouping behavior is as described in Priority grouping. For Non-secure interrupts, priority grouping is modified so that, for each binary point value, one bit moves from the subpriority field to the group priority field.
Priority grouping always operates on the priority value held in the Distributor, not the value visible to a Non-secure read of the priority value corresponding to a Non-secure interrupt. See Figure 3.5 and Figure 3.6.
Table 3.2 shows the priority grouping for Non-secure interrupts.
Table 3.4. Priority grouping for Non-secure interrupts
| Binary point value | Interrupt priority field [7:0] | ||
|---|---|---|---|
| Group priority field | Subpriority field | Field with binary point | |
| 0 | [7:0] [1] | - | gggg gggg. |
| 1 | [7:1] [1] | [0] | ggg gggg.s |
| 2 | [7:2] [1] | [1:0] | gg gggg.ss |
| 3 | [7:3] [1] | [2:0] | g gggg.sss |
| 4 | [7:4] [1] | [3:0] | gggg.ssss |
| 5 | [7:5] [1] | [4:0] | ggg.ssss s |
| 6 | [7:6] [1] | [5:0] | gg. ssss ss |
| 7 | [7] [1] | [6:0] | g.ssss sss |
[1] If a Non-secure write sets the priority value field for a Non-secure interrupt then bit [7] is 1. | |||
The right shift of the binary point for Non-secure interrupts, and the views of interrupt priority described in Software views of interrupt priority, mean that software that has no awareness of the Security Extensions sees the same priority grouping mechanism regardless of whether it is running in Secure state or in Non-secure state.
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