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STM32L4 default DFU mode verus Standalone

Question asked by Renschler.Uwe on Aug 5, 2015
Latest reply on May 5, 2016 by cortez.israel
We used the DFUSE over USB successfully with several L152 designs. The L152 chips don t have a USB boot loader DFU like described in the AN2606 STM32 microcontroller system memory boot mode. (DFU SE via USB) So we download the slightly modified standalone DFU USB loader and everything works perfect with the L152 chips. We hoped to save this work with the L476 chips, cause there the DFU loader is already preprogrammed from factory.

I thought on the L476 devices the DFU over USB is preprogrammed from factory and all we have to do is to have a 32kHz Xtal and have the BOOT0 pin connected to ground (pattern 7). But this doesn t work like expected.
I also found on the Cube, that there is a DFUSE standalone project, which exactly does, what we want.
Can anybody explain, why there is this DFUSE standalone project, if ST already have preprogrammed this code directly at factory ?
Is the factory preprogrammed code more sensitive to 100% correct USB power settings or should it also work with 3.0 Volts ? Further explanation about the intentions of the 2 different DFU loaders would be highly appreciated.