ROM bootloader code

[PeterR]

Where is the ROM bootloader code? Or where are both ESP and remote ends of a serial flasher?
We ported the esptool code to 'C' to program the ESP from another processor. The software works fine but we have run into hardware difficulties when trying to control RIO0 from both programming jig and processor.

The simplest get out is to place a copy of the ROM bootloader in flash.
We could also write our own or switch to ANO serial bootloaders but are looking for an 'out of the box' polished solution.

[WiFive]

It is closed source. But you can look at the stub loader code in esptool. Why can't you fix the hardware issue?