LM3S2B93 Datasheet, PDF (92/1194 Pages) Texas Instruments – Stellaris® LM3S2B93 Microcontroller

The Cortex-M3 Processor
2.4.5
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™-M3/M4 Instruction Set
Technical User's Manual.
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 92. 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 92. For the specific address range of the bit-band regions,
see Table 2-4 on page 87.
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
Address Range
Memory Region
0x2000.0000 - 0x200F.FFFF SRAM bit-band region
0x2200.0000 - 0x23FF.FFFF SRAM bit-band alias
Instruction and Data Accesses
Direct accesses to this memory range behave as SRAM 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 remapped.
Table 2-7. Peripheral Memory Bit-Banding Regions
Address Range
Memory Region
Instruction and Data Accesses
0x4000.0000 - 0x400F.FFFF Peripheral bit-band region Direct accesses to this memory range behave as peripheral
memory accesses, but this region is also bit addressable through
bit-band alias.
0x4200.0000 - 0x43FF.FFFF Peripheral 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.
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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January 20, 2012
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