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Dualbank Flash Programming

The ST STM32L4 series devices come with a dual-bank flash memory. The layout of the dual-bank flash memory can be configured by the user through the option byte DUALBANK. By default, the value of this option byte is DUALBANK == 1, which means that the flash is configured as dual bank memory while DUALBANK == 0 means that the flash is configured as single bank memory flash. In dual-bank mode, the flash boot source can be switched between bank 1 or bank 2. In single-bank mode, flash always boots from bank 1. The total flash size is exactly the same for both modes. Another advantage of using DUALBANK is that both banks can be accessed in parallel (e.g. reading bank 1 while programming bank 2).

Problem description

The flash algorithm has to behave differently, depending on the active flash bank mode configuration as the flash controller expects different page indices for the same destination address.


When using the J-Link flash loader, make sure that the flash controller is configured for dual bank flash layout (DUALBANK == 1), which is the default.

STM32L476xx (Q)SPI support

The ST STM32L476xx device series comes with a QUADSPI controller which allows memory mapped read accesses to any (Q)SPI flash, connected to the Quad-SPI interface of the MCU. This allows the J-Link DLL to support flash programming through the Quad-SPI interface. Unfortunately, there is no generic way how to implement flash programming because the used pins to connect the SPI flash is not defined. Different pins can be used for the same QUADSPI alternate function and therefore, for each configuration, a slightly different RAMCode (different pin initialization / flash size) is required. We have developed two flash algorithms based on a different pin layout. One is based on the ST STM32L476-DISCO evaluation board, the other one is based on the ST STM32L476G Eval board. These flash algorithms can be used to to program any common (Q)SPI flash, connected to the Quad-SPI interface of the ST STM32L476 device. The flash algorithms are based on the SEGGER Open Flash Loader concept so they can easily be exchanged if a pin configuration, different from the one used in the example flash algorithms, is required. In such cases, please get in touch with SEGGER directly (

For further information regarding this as well as the flash algorithms, please refer to the following pages: