ARM Cortex-M4 - Binary Point

Cortex-M4 Peripherals
ARM DUI 0553A Copyright © 2010 ARM. All rights reserved. 4-18
ID121610 Non-Confidential
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. Table 4-18
shows how the PRIGROUP value controls this split. Implementations having fewer than 8-bits
of interrupt priority treat the least significant bits as zero
Note
Determining preemption of an exception uses only the group priority field, see Interrupt priority
grouping on page 2-25.
Table 4-18 Priority grouping
Interrupt priority level value, PRI_N[7:0] Number of
PRIGROUP Binary point
a
Group priority bits Subpriority bits Group priorities Subpriorities
0b000 bxxxxxxx.y [7:1] [0] 128 2
0b001 bxxxxxx.yy [7:2] [1:0] 64 4
0b010 bxxxxx.yyy [7:3] [2:0] 32 8
0b011 bxxxx.yyyy [7:4] [3:0] 16 16
0b100 bxxx.yyyyy [7:5] [4:0] 8 32
0b101 bxx.yyyyyy [7:6] [5:0] 4 64
0b110 bx.yyyyyyy [7] [6:0] 2 128
0b111 b.yyyyyyyy None [7:0] 1 256
a. PRI_n[7:0] field showing the binary point. x denotes a group priority field bit, and y denotes a subpriority field bit.