STM32L4 bootloader port filtering ?

[Noyb]

Posted on September 11, 2017 at 09:50

STM32L4, using internal bootloader, I can start it yet I need it not to open all available ports (usart, spi, usb) but limit it to only one dedicated uart port to avoid waking up chips linked to the other ports. Is there a way to filter ports before entering bootloader, like setting a register with bitfield to allow/disable certain ports ?

[Tesla DeLorean]

Posted on September 11, 2017 at 12:25

It tests other ports rather than open them. 

If you want different behaviour you must write your own loader code.

[Noyb]

Posted on September 11, 2017 at 12:45

Well, by testing ports, it get them out from high impedance, thus wake the attached chips. I wondered if there was a way to block some port scanning. Is the internal bootloader's source code available so that I could 'just' switch the unneeded part out ?

[Tesla DeLorean]

Posted on September 11, 2017 at 13:08

No source, functionality in ROM, can be disassembled if exact behaviour is of interest. Pretty sure it sets USART_RX pins as Input to TIM to measure baud from 0x7F pattern.