Nios II Classic Processor Reference Guide

ID 683620
Date 10/28/2016
Document Table of Contents The MASK Field

When the amount of memory reserved for a region is defined by size, the MASK field specifies the size of the memory region. The MASK field is the same number of bits as the BASE field of the mpubase register.

Note: Unused high-order or low-order bits must be written as zero and are read as zero.

MASK Region Size Encodings Table lists the MASK field encodings for all possible region sizes in a full 31-bit byte address space.

Table 34.  MASK Region Size Encodings
MASK Encoding Region Size
0x1FFFFFF 64 bytes
0x1FFFFFE 128 bytes
0x1FFFFFC 256 bytes
0x1FFFFF8 512 bytes
0x1FFFFF0 1 KB
0x1FFFFE0 2 KB
0x1FFFFC0 4 KB
0x1FFFF80 8 KB
0x1FFFF00 16 KB
0x1FFFE00 32 KB
0x1FFFC00 64 KB
0x1FFF800 128 KB
0x1FFF000 256 KB
0x1FFE000 512 KB
0x1FFC000 1 MB
0x1FF8000 2 MB
0x1FF0000 4 MB
0x1FE0000 8 MB
0x1FC0000 16 MB
0x1F80000 32 MB
0x1F00000 64 MB
0x1E00000 128 MB
0x1C00000 256 MB
0x1800000 512 MB
0x1000000 1 GB
0x0000000 2 GB

The MASK field contains the following value, where region_size is in bytes:

MASK = 0x1FFFFFF << log2(region_size >> 6)