PM0056 datasheet(29/156 Pages) STMICROELECTRONICS

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PM0056

The Cortex-M3 processor

A word access to the SRAM or peripheral bit-band alias regions map to a single bit in the

SRAM or peripheral bit-band region.

The following formula shows how the alias region maps onto the bit-band region:

bit_word_offset = (byte_offset x 32) + (bit_number x 4)

bit_word_addr = bit_band_base + bit_word_offset

Where:

•

Bit_word_offset is the position of the target bit in the bit-band memory region.

•

Bit_word_addr is the address of the word in the alias memory region that maps to the

targeted bit.

•

Bit_band_base is the starting address of the alias region.

•

Byte_offset is the number of the byte in the bit-band region that contains the targeted

bit.

•

Bit_number is the bit position, 0-7, of the targeted bit.

Figure 10 on page 29 shows examples of bit-band mapping between the SRAM bit-band

alias region and the SRAM bit-band region:

•

The alias word at 0x23FFFFE0 maps to bit[0] of the bit-band byte at

0x200FFFFF: 0x23FFFFE0 = 0x22000000 + (0xFFFFF*32) + (0*4).

•

The alias word at 0x23FFFFFC maps to bit[7] of the bit-band byte at

0x200FFFFF: 0x23FFFFFC = 0x22000000 + (0xFFFFF*32) + (7*4).

•

The alias word at 0x22000000 maps to bit[0] of the bit-band byte at

0x20000000: 0x22000000 = 0x22000000 + (0*32) + (0 *4).

•

The alias word at 0x2200001C maps to bit[7] of the bit-band byte at

0x20000000: 0x2200001C = 0x22000000+ (0*32) + (7*4).

Figure 10. Bit-band mapping

0x23FFFFE4

0x22000004

0x23FFFFE0

0x23FFFFE8

0x23FFFFEC

0x23FFFFF0

0x23FFFFF4

0x23FFFFF8

0x23FFFFFC

0x22000000

0x22000014

0x22000018

0x2200001C

0x22000008

0x22000010

0x2200000C

32MB alias region

0x20000000

0x20000001

0x20000002

0x20000003

0x200FFFFC

0x200FFFFD

0x200FFFFE

0x200FFFFF

1MB SRAM bit-band region

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