it can't boot to dfu mode.

[xaqfan]

I have a Nordic 52840 hardware, which comes with the bootloader. Learned that the register GPREGRET address is 0x4000051C. The app is written in rust language, and the address is assigned 0xB1 directly in the app. But  it can't  enter the dfu mode.
code show as below:

let gpregret = 0x4000051Cusize;
         let pa = gpregret as * mut i32;
         unsafe {
             * pa = 0xB1;
         };

Am I writing it wrong?

thank you!

[Einar Thorsrud]

Hi,

I addition to the excellent points by Hanno Braun, I also want to mention the following which may or may not be relevant (it is not clear from the question):

• The nRF5 devices do not ship with a bootloader by default, so unless you (or someone else) has programmer the bootloader, it is not there.
• After writing the magic word (0xB1) to the retention register, you need to do a soft reset in order for the bootloader to run.

[xaqfan]

How implement NVIC_SystemReset() function  by rust?

[Einar Thorsrud]

If you are running code on the nRF that you write in Rust, then you must have the basic infrastructure in place, and I would be very surprised if it did not support core ARM functions such as NVIC reset. I do not know any details about what you are using though, so I cannot say more. Please note that Rust is not officially supported. If you want to do some real work, then I suggest you use the nRF5 SDK and program in C. If you use rust for fun or research that is, of course, fine, but you are more or less on your own.

[xaqfan]

Google have  an opensource on github with nordic hardware, it's name opensk.

I can flash app .And I what enter DFU mode to update with button less.

But i have no idea.