Thanks for your answer.
Yes, i already know this app note. I have written my loader after this app note. But my loader does not work.
I download parsed image file in 4096 byte blocks,
read each 4096 byte block back to verify content (content looks ok), then as final step i send a "jump to address x".
Then FX3 (originally as VID=1480, PID=0000) goes away from USB bus, but does not appear again.
When i take USB power away, i can do the same again.
Therefore my question, if something is needed before or after the download and jump sequence to bring
the FX3 back to life after loading my own software.
When i load the same image with Control Center on another computer, it enumerates with new VID / PID and everything is ok.
If you follow the software example in the application note then the device should program. There are really only two steps - download the .img file and when finished transfer execution to program entry. Note that the downloaded block will not always be 4096 if it is at the end of a download section. For example a download section might be 34768 bytes long which will be 8 downloads of 4096 and a final download of 2000 bytes. I have attached a text file showing Visual Basic code to download the image file. This works.
fw_dload.txt.zip 1.1 K
I have my download util running now. I can confirm that only write to SRAM in max 4096 byte chunks and execute is needed.
All other things work automatically.