Bootloader code sequence

AN3156

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DocID017068 Rev 4

Figure 1. Bootloader for STM32 connectivity line devices

1. After system reset, the device may return to the BL_DFU loop or execute code from Flash memory/RAM

depending on the connection states and the boot pin status.

2. Leave DFU is achieved by a 0 Data Download request followed by GetStatus request and Device Reset.

3. After six trials (the three clock configurations are tested twice), a System Reset is generated.

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If the product uses HSE for the USB operation (except Connectivity Line):

–

At startup the HSE is measured (if present) and if it is supported the USB is

configured. If the HSE is not detected the Bootloader will perform a system reset.

If the measured value of the HSE clock is unsupported value, the USB protocol

will not function correctly.

•

If the product uses the HSI for the USB operation.

–

At startup the USB is configured using HSI clock.

Refer to AN2606 for more details about product's configuration.