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PM0214 Rev 10 33/262

PM0214 The Cortex-M4 processor

261

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 9 on page 33 shows examples of bit-band mapping between the SRAM bit-band

alias region and the SRAM bit-band region:

• The alias word at 0x23FFFFED maps to bit[0] of the bit-band byte at

0x200FFFFF: 0x23FFFFED = 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 9. Bit-band mapping

Directly accessing an alias region

Writing to a word in the alias region updates a single bit in the bit-band region.

Bit[0] of the value written to a word in the alias region determines the value written to the

targeted bit in the bit-band region. Writing a value with bit[0] set to 1 writes a 1 to the bit-

band bit, and writing a value with bit[0] set to 0 writes a 0 to the bit-band bit.

Bits[31:1] of the alias word have no effect on the bit-band bit. Writing 0x01 has the same

effect as writing 0xFF. Writing 0x00 has the same effect as writing 0x0E.

0x23FFFFE4

0x22000004

0x23FFFFE00x23FFFFE80x23FFFFEC0x23FFFFF00x23FFFFF40x23FFFFF80x23FFFFFC

0x220000000x220000140x220000180x2200001C 0x220000080x22000010 0x2200000C

32MB alias region

7 0

0x200000000x200000010x200000020x20000003

6 5 4 3 2 1 07 6 5 4 3 2 1 7 6 5 4 3 2 1 07 6 5 4 3 2 1

07 6 5 4 3 2 1 6 5 4 3 2 107 6 5 4 3 2 1 07 6 5 4 3 2 1

0x200FFFFC0x200FFFFD0x200FFFFE0x200FFFFF

1MB SRAM bit-band region

ST STM32H757 User Manual

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