PM0214 Datasheet, PDF (31/245 Pages) STMicroelectronics – This programming manual provides information

PM0214
The Cortex-M4 processor
2.2.5
Bit-banding
A bit-band region maps each word in a bit-band alias region to a single bit in the bit-band
region. The bit-band regions occupy the lowest 1 MB of the SRAM and peripheral memory
regions.
The memory map has two 32 MB alias regions that map to two 1 MB bit-band regions:
• Accesses to the 32 MB SRAM alias region map to the 1 MB SRAM bit-band region, as
shown in Table 14
• Accesses to the 32 MB peripheral alias region map to the 1 MB peripheral bit-band
region, as shown in Table 15.
Address
range
0x20000000-
0x200FFFFF
0x22000000-
0x23FFFFFF
Table 14. SRAM memory bit-banding regions
Memory
region
Instruction and data accesses
SRAM bit-band region
Direct accesses to this memory range behave as SRAM memory
accesses, but this region is also bit addressable through bit-band alias.
SRAM bit-band alias
Data accesses to this region are remapped to bit band region. A write
operation is performed as read-modify-write. Instruction accesses are not
remapped.
Address
range
0x40000000-
0x400FFFFF
0x42000000-
0x43FFFFFF
Table 15. Peripheral memory bit-banding regions
Memory
region
Instruction and data accesses
Peripheral
bit-band region
Peripheral
bit-band alias
Direct accesses to this memory range behave as peripheral memory
accesses, but this region is also bit addressable through bit-band
alias.
Data accesses to this region are remapped to bit-band region. A write
operation is performed as read-modify-write. Instruction accesses are
not permitted.
Note:
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.
Bit band accesses can use byte, halfword, or word transfers. The bit band transfer size
matches the transfer size of the instruction making the bit band access.
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
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