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
PRIGROUP	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:

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 Interrupt Priority Grouping.