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.

Table 2-50. Priority Grouping
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
Note:
  1. 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.