Boot Configuration; Table 2. Boot Modes - ST STM32F412 Reference Manual

RM0402
Reading address 0x22006008 returns the value (0x01 or 0x00) of bit 2 of the byte at SRAM1
address 0x20000300 (0x01: bit set; 0x00: bit reset).
For more information on bit-banding, refer to the Cortex
manual (see
2.6

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 STM32F412xx, three different boot modes can be selected through the BOOT[1:0]
pins as shown in
Boot mode selection pins
BOOT1
x
0
1
The values on the BOOT pins are latched on the 4th rising edge of SYSCLK after a reset. It
is up to the user to set the BOOT1 and BOOT0 pins after reset to select the required boot
mode.
BOOT0 is a dedicated pin while BOOT1 is shared with a GPIO pin. Once BOOT1 has been
sampled, the corresponding GPIO pin is free and can be used for other purposes.
The BOOT pins are also resampled when the device exits the Standby mode. Consequently,
they must be kept in the required Boot mode configuration when the device is in the Standby
mode. After this startup delay is over, the CPU fetches the top-of-stack value from address
0x0000 0000, then starts code execution from the boot memory starting from 0x0000 0004.
Note: When the device boots from SRAM, in the application initialization code, you have to
relocate the vector table in SRAM using the NVIC exception table and the offset register.
Related documents on page
Table 2.

Table 2. Boot modes

Boot mode
BOOT0
0 Main Flash memory Main Flash memory is selected as the boot space
1 System memory
1 Embedded SRAM
RM0402 Rev 6
®
-M4 with FPU programming
1).
®
-M4 with FPU CPU always
System memory is selected as the boot space
Embedded SRAM is selected as the boot space
Aliasing
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