Modifying Option Byte Value from Program Running in SRAM and Loaded using dfu-util

[mykepredko]

I want to write a program for a fresh (first time power applied to it so there is nothing in Flash) STM32G0B1 that executes in RAM, resets the nBOOT_SEL bit in the Option Bytes (to allow DFU Mode to be invoked when Flash has been written).  

The reason why I want to execute in RAM is to avoid having to run a program that is loaded in Flash (and resets nBOOT_SEL as discussed above) which is loaded into Flash that requires a power cycle to restart so that DFU Mode can be enabled in the MCU to load the actual product firmware.  

This is being done in manufacturing test, so avoiding a power cycle (which takes about a minute due to other hardware in the application) would be of advantage.  

Could anybody point me to:

1. A dfu-util statement that a bin file at a specific SRAM address and has execution continue from there
2. Pointers to how the application would be configured.  What I have found so far are:
   1. https://community.st.com/t5/stm32-mcus/how-to-place-and-execute-stm32-code-in-sram-memory-with/ta-p/49528
   2. https://stackoverflow.com/questions/42612329/executing-code-from-ram-in-stm32
   3. https://stackoverflow.com/questions/69598820/how-does-one-run-code-from-ram-on-a-stm32
   4. https://stackoverflow.com/questions/55389711/stm32f7-execute-code-from-ram-and-flash
3. In my research, it seems like the USB as well as another interrupt needs to be disabled while running an application like this.  Does anybody have any references which explains what is required?

I think the last two links for creating a program that runs in SRAM are probably closest to what I want to do but I'm hoping that there is a crisp explanation that I can follow.  

For resetting the nBOOL_SEL bit, I'm going to use the following guide (with standard STM/HAL development tools/libraries):

https://community.st.com/t5/stm32-mcus/how-to-program-stm32-option-bytes-with-the-hal-api/ta-p/49660

Any comments or suggestions are most welcome!

myke

[mykepredko]

I wanted to follow up with this - I've got an application running that resets the nBOOT_SEL bit but now I need to get it running in SRAM after being loaded into the STM32G0B1RET6 MCU using DFU.  

First I created a simple application to Flash an LED on the test board, I created a .bin version of it and loaded it using DFU:

As you can see in the screenshot above, the download takes place without issue.  

The only problem I have is that the code won't start executing after I load it - I have tried adding the ":leave" modifier but no joy.  If I reset the board, the code works fine with the LED flashing as expected.  

---

For testing in SRAM, I fully erase the MCU to make sure I don't get any unexpected results from a previous Flash load.

I created a new project with the same main.c as the first case but with the following changes:

1. In "STM32G0B1RETX_FLASH.ld" and "STM32G0B1RETX_RAM.ld", I set the memory definition as:

MEMORY
{
  RAM    (xrw)    : ORIGIN = 0x20002000,   LENGTH = 144K
  FLASH  (rx)     : ORIGIN = 0x20000000,   LENGTH = 512K
}

• Next, in system_stm32g0xx.c I uncommented the lines containing "#define USER_VECT_TAB_ADDRESS" and "#define VECT_TAB_SRAM" to change the Vector Table into SRAM rather than in Flash.  
• After building the application, I checked to see that the (fully erased) MCU was in DFU Mode and then attempted to download the application with the results (failing at the end):

• I then attach S-Link, connect (without touching anything on the board including power or the USB cable) and look at the contents of SRAM and see:

• This ain't great because when I look at the contents of the .bin file I see:

So, the immediate issues I see here are:

1. There is a problem with the SRAM download (see point 3. above stating that the "last page" isn't writeable). 
2. The contents of SRAM aren't what I expect.  I've never done this before so I don't know what to expect but I think it's reasonable to think that I should see the contents of the .bin file at some location.   

So, any ideas?  

@clkr , I've seen your post and, I'm not disabling the interrupts used by DFU - I think this explains why the Flashed version doesn't start (I've tried it with both with and without the ":leave" Modifier to the "-s" dfu-util option.  

Thanx - I feel like it's something simple but I really can't figure out what I'm doing wrong. 

myke