Boot Configuration; Table 2. Boot Modes - ST STM32F405 Reference Manual

RM0090
are only available for Cortex
DMA).
A mapping formula shows how to reference each word in the alias region to a corresponding
bit in the bit-band region. The mapping formula is:
bit_word_addr = bit_band_base + (byte_offset x 32) + (bit_number × 4)
where:
–
–
–
–
Example
The following example shows how to map bit 2 of the byte located at SRAM address
0x20000300 to the alias region:
0x22006008 = 0x22000000 + (0x300*32) + (2*4)
Writing to address 0x22006008 has the same effect as a read-modify-write operation on bit
2 of the byte at SRAM address 0x20000300.
Reading address 0x22006008 returns the value (0x01 or 0x00) of bit 2 of the byte at SRAM
address 0x20000300 (0x01: bit set; 0x00: bit reset).
For more information on bit-banding, please refer to the Cortex
manual (see
2.4

Boot configuration

Due to its fixed memory map, the code area starts from address 0x0000 0000 (accessed
through the ICode/DCode buses) while the data area (SRAM) starts from address
0x2000 0000 (accessed through the system bus). The Cortex
fetches the reset vector on the ICode bus, which implies to have the boot space available
only in the code area (typically, Flash memory). STM32F4xx microcontrollers implement a
special mechanism to be able to boot from other memories (like the internal SRAM).
In the STM32F4xx, three different boot modes can be selected through the BOOT[1:0] pins
as shown in
Boot mode selection pins
BOOT1
x
0
1
®
-M4 with FPU accesses, and not from other bus masters (e.g.
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
Related documents on page
Table 2.
Boot mode
BOOT0
0 Main Flash memory Main Flash memory is selected as the boot space
1 System memory
1 Embedded SRAM
1).

Table 2. Boot modes

System memory is selected as the boot space
Embedded SRAM is selected as the boot space
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Memory and bus architecture
®
-M4 with FPU programming
®
-M4 with FPU CPU always
Aliasing
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