ST STM32L4x6 Reference Manual page 77

RM0351
1. When the FSMC is remapped at address 0x0000 0000, only the first two regions of bank 1 memory controller
(bank 1 NOR/PSRAM 1 and NOR/PSRAM 2) can be remapped. When the QUADSPI is remapped at address
0x0000 0000, only 128 MB are remapped. In remap mode, the CPU can access the external memory via
ICode bus instead of system bus which boosts up the performance.
2. Even when aliased in the boot memory space, the related memory is still accessible at its original memory
space.
Embedded boot loader
The embedded boot loader is located in the System memory, programmed by ST during
production. Refer to AN2606 STM32 microcontroller system memory boot mode.
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