2.7.2.5.1 Binary Point
The PRIGROUP field indicates the position of the binary point that splits the PRI_n fields in the Interrupt Priority Registers into separate group priority and subpriority fields. The following table shows how the PRIGROUP value controls this split. If you implement fewer than 8 priority bits you might require more explanation here, and want to remove invalid rows from the table, and modify the entries in the number of columns.
PRIGROUP | Interrupt priority level value, PRI_N[7:0] | Number of | |||
---|---|---|---|---|---|
Binary point 1 | Group priority bits | Subpriority bits | Group priorities | Subpriorities | |
b000 | bxxxxxxx.y | [7:1] | [0] | 128 | 2 |
b001 | bxxxxxx.yy | [7:2] | [1:0] | 64 | 4 |
b010 | bxxxxx.yyy | [7:3] | [2:0] | 32 | 8 |
b011 | bxxxx.yyyy | [7:4] | [3:0] | 16 | 16 |
b100 | bxxx.yyyyy | [7:5] | [4:0] | 8 | 32 |
b101 | bxx.yyyyyy | [7:6] | [5:0] | 4 | 64 |
b110 | bx.yyyyyyy | [7] | [6:0] | 2 | 128 |
b111 | b.yyyyyyyy | None | [7:0] | 1 | 256 |
- PRI_n[7:0] field showing the binary point. x denotes a group priority field bit, and y denotes a subpriority field bit.
Determining preemption of an exception uses only the group priority field, see 2.5.3.6 Interrupt Priority Grouping.