rohit,
Before you worry about what comes out of the USART, you need to make sure all the parts of your code work first. You have three things you're doing in your code, but it sounds like you have no idea if all three are working. The three things you're doing are:
1: Writing a value to FLASH
2: Reading the value you wrote from FLASH
3: Sending that value over the USART
The first thing to do is check if your USART is setup and working properly. Comment out all the code your showed in your post code and replace it with something simple like:
uint8_t ValueToSend = 0xAB;
HAL_UART_Transmit(&huart1, &ValueToSend, 1, 200);
Note that I also opened up the timeout value as you don't want that to be an issue. When you run this, your should see the hex value 0xAB appear using whatever code or device you are using to test with. Personally, I'dd just use a regular ASCII character and a serial terminal to verify this as it's probably easier to make sure the test works. Something like this:
uint8_t ValueToSend = 'A';
HAL_UART_Transmit(&huart1, &ValueToSend, 1, 200);
You'd expect to see the letter "A" appear in your serial terminal. Don't assume your USART HAL call is working. Test it and verify it.
Next, comment out the USART code and just try your FLASH write and read code. Set a breakpoint at this line in your code:
const volatile uint8_t *userConfig=(const volatile uint8_t *)0x0801F800;
Single step through the line and see what value appears in "userConfig". Hopefully you know how to use a debugger and set breakpoints. If you don't know how to, then go do some Google searching and learn how. Learning proper use of a debugger will make your life 1000% easier.
Once you try the two tests I suggested, you'll know if the problem lies in your UASRT code or your FLASH read/write code and you can start troubleshooting from there.
Also, your line to to read from the FLASH address is like a keyword buffet. Instead of trying to do everything in one line, break it up a bit. Also, since you don't know what is or isn't working, don't do all the elaborate casting. Do this instead:
uint8_t* userConfig;
userConfig = (uint8_t *)0x0801F800;
HAL_UART_Transmit(&huart1, userConfig, 1, 200);
Much simpler to read and understand what's going on. Also much easier to not make a mistake writing. If you get this working, then you start adding back your "const volatile" and see if things still work. That's assuming you even need those, which I don't think you do.
Remember, the key to debugging is breaking things down to simple pieces, testing those simple pieces, and then adding together the pieces that work until you get the whole thing working. And using a debugger (and setting breakpoints) will make is all simple.
