If the system contains a memory map switching mechanism, use a
DSB
instruction after switching
the memory map in the program. The
DSB
instruction ensures subsequent instruction execution
uses the updated memory map.
■ Dynamic exception priority change
When an exception priority has to change when the exception is pending or active, use
DSB
instructions after the change. The change then takes effect on completion of the
DSB
instruction.
Memory accesses to Strongly Ordered memory, such as the System Control Block, do not require
the use of
DMB
instructions.
For more information on the memory barrier instructions, see the Cortex™-M4 instruction set chapter
in the
ARM® Cortex™-M4 Devices Generic User Guide (literature number
)
.
2.4.5
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. Accesses
to the 32-MB SRAM alias region map to the 1-MB SRAM bit-band region, as shown in Table
2-6 on page 109. Accesses to the 32-MB peripheral alias region map to the 1-MB peripheral bit-band
region, as shown in Table 2-7 on page 109. For the specific address range of the bit-band regions,
see Table 2-4 on page 103.
Note:
A word access to the SRAM or the peripheral bit-band alias region maps to a single bit in
the SRAM or peripheral bit-band region.
A word access to a bit band address results in a word access to the underlying memory,
and similarly for halfword and byte accesses. This allows bit band accesses to match the
access requirements of the underlying peripheral.
Table 2-6. SRAM Memory Bit-Banding Regions
Instruction and Data Accesses
Memory Region
Address Range
End
Start
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 region
0x2006.FFFF
0x2000.0000
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.
SRAM bit-band alias
0x2234.FFFF
0x2200.0000
Table 2-7. Peripheral Memory Bit-Banding Regions
Instruction and Data Accesses
Memory Region
Address Range
End
Start
Direct accesses to this memory range behave as
peripheral memory accesses, but this region is also bit
addressable through bit-band alias.
Peripheral bit-band
region
0x400F.FFFF
0x4000.0000
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.
Peripheral bit-band alias
0x43FF.FFFF
0x4200.0000
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)
109
June 18, 2014
Texas Instruments-Production Data
Tiva
™
TM4C1294NCPDT Microcontroller