Arduino for STM32

hello expert

I'm currently using a STM32F103RDT6 and I'm developing it via Arduino IDE.

Among the upload methods of Arduino IDE, I am uploading firmware through ST-LINK, but it is cumbersome to continuously use ST-LINK due to the structure of the hardware I am making. And modifying this hardware is difficult.
So I want to upload firmware by Serial Method.
Serial communication uses USART3 connected by FTDI.

Can I upload serially via USART3?
I can't go any further as I don't have any expertise in this area.

If there is a way to upload it serial, even a small tip would be fine, please advise.

You can refer to this:
https://www.st.com/resource/en/applicat ... ronics.pdf

It seems only USART1 allows Serial upload.

@fpiSTM

Thank you for answer.

So, is there any way to use USART3 pins (PC10,11) as USART1?
Please tell me everything except how to jump on the circuit.

Well, if you want use USART3 then you will have to implement your own bootloader.

@fpiSTM

I understand what you mean

Thank you very much for your reply. It was a big help.

@fpiSTM

Following your advice, I tried to build a new bootloader.

I tried to assign functions to pins by selecting STM32F103RDT6 through STM32CudeMX, but I could only select USART3 for PC10 and 11 pins.
(I want to give USART1 function to PC10,11.)

Is it different from the way you advised?

You cannot assign any pin to any interface. PC10 and PC11 can be assigned only to UART4 or USART3.
Here's STM32F103RD datasheet:
https://www.st.com/resource/en/datashee ... f103rd.pdf