Hi,
I want to build a custom made arduino pro-mini according to this page:
In order to upload code using an external FTDI chip, do I need to set a bootloader the first time or any time? or is it enough to use DTR/RX/TX pins to do that? I do not want to use SPI pins to save space.
In addition I will be glad for any links explaining the bootloader uses for atmega chips because I didn't find anything informative.
Thanks.
omri_saporta:
do I need to set a bootloader the first time
Yes. You won't be able to upload to your board via the FTDI if there is no bootloader on the ATmega328P.
omri_saporta:
is it enough to use DTR/RX/TX pins to do that
No. That's not possible.
omri_saporta:
I do not want to use SPI pins to save space.
I don't understand what you mean by that. Please provide a detailed explanation so we can be able to correctly answer your questions.
You only need to connect an ISP programmer to the pins long enough to burn the bootloader. After that, you can disconnect the programmer so it won't take up any space.
omri_saporta:
In addition I will be glad for any links explaining the bootloader uses for atmega chips because I didn't find anything informative.
The bootloader is a program that runs after you reset the Pro Mini. It listens for communication over the serial port. If it sees the communication with the computer that happens when an upload starts, then it takes the incoming data and writes it to the flash memory. It can also read the memory and send it back over the serial connection so that the program can be verified or downloaded from the ATmega328P.
I used a USBasp to upload the bootloader and then an FTDI to upload the sketch, thereafter.
I used Minicore for the bootloader btw
Thanks a lot for the quick response!
Making sure I understand correctly, I need to upload the bootloader only once for it to understand where to upload the code from, and then every time I upload the code through FTDI(to the chip memory), it will know to withdraw it from there?
-In esp32 for example, you don't need to burn the bootloader, is it burned in advanced for all their chips?
-Another question, I know there is an option for an arduino pro mini to boot right away with the code, without the sequence of it searching for it(takes a few seconds), how do I do that?
Sorry if I made a mess 
Thanks.
omri_saporta:
Making sure I understand correctly, I need to upload the bootloader only once for it to understand where to upload the code from, and then every time I upload the code through FTDI(to the chip memory), it will know to withdraw it from there?
Correct.
omri_saporta:
-In esp32 for example, you don't need to burn the bootloader, is it burned in advanced for all their chips?
Yes, it's programmed permanently in the chip's ROM when it's made.
omri_saporta:
-Another question, I know there is an option for an arduino pro mini to boot right away with the code, without the sequence of it searching for it(takes a few seconds), how do I do that?
When you do that, the chip is erased (which will erase the bootloader, if present). Then the sketch program is uploaded to the chip.