stm32f407 dfu bootloader not working and got wrong flash size

[gazam]

hi. I made 10 sample boards.

and 3 board are working strange.

I tested dfu bootloader in system memory with usb. (boot mode BOOT0 = 1)

7 boards are working fine with my firmware and bootloader.

buy 3 boards are working only with my firmware. it can not go into dfu mode.

I use 25Mhz Hse crystal. and my firmware use 168Mhz system clock and USB system work fine.

So I tried to find the problem and I found something strange thing.

I read mcu information from ST-Link Utility.

Normal(working fine) board shows correct information

my mcu is STM32F407IE that has 512KB flash memory . so captured screen(407normal) shows correct size.

but 407wrong file show flash size with unknown.

It seems like it has a 1MB flash.

and I tested read/write memory over 512KB space.

I got a error message from normal boards but three borads are working !

and the three board are now have a problem with DFU.

I used latest ST-Link Utility(4.3.0) and latest ST-LINK V2 firmware. ​

How can this happen?

​please help me.