As far as I see the secondary CPU on the UNO the atmega8-16pu is used only as a USB to rs323 adapter and nothing more,
that could be done with some ftdi. As its build with a CPU that has even some pins free, why not wire it such that you can plug a empty ATmega328 and write the bootloader to it with the UNO board, where the aux CPU would act as a ISP programmer?
Anyways, why has there been used a aux CPU and not just a ftdi chip in the first place?
Trax
FTDI chip is not re-programmable for other functions, so 8U2/1U2 offers that advantage.
Cost might been an issue, 16U2s being a little less than FT232R. Maybe a better deal was made with large purchases of 328P, 2560, 32U4, add in 16U2 ...
Writing code to have 16U2 control 328P via user adding some jumpers from ICSP to ICSP certainly seems possible as a means to reinstall bootloader, or for bootloaderless code install.
Yea, so why not make a 4th uno revision with that capability?
Don't need a 4th one - just different code for the existing one.
The onboard FTDI chip on the old duemilanove:
http://make.kosakalab.com/arduino/bootloader/bitbang_w_ide_en.html
Just come up with code that can be loaded into the 16U2 to do the same.
ok why than is that not a standard featue?
It would be extreemly usefull for the UNOs, as one if thair main advantages is that you can replace the atmega after killing it and ocntinue with furtzer experiments.